2.7 Gene Expression

WHAT YOU SHOULD ALREADY KNOW FROM YEAR 11 FOR THIS.DNA Structure – Double helix, phosphate-sugar backbone,

Base parings A-T, C-G. Nucleotide monomer (Phosphate, Sugar & Base)

Gene A section of DNA that codes for a particular protein/trait (ie. Hair type)

Allele An alternative form of a gene (ie. Straight hair vs Curly Hair)

Genotype The specific pair of alleles (on homologous chromosomes) that the organism carries for a particular trait.

Phenotype The physical expression of the alleles an organism carries.

Chromosome A DNA molecule that is coiled up tightly (around histones – packaging proteins).

Mutation A permanent change in the DNA base sequence (this may result in a new allele).

DNA

DNA

• DNA stands for Deoxyribose nucleic acid• DNA is a very large molecule• It is made two strands of molecules which are

twisted together in the shape of a Double Helix. • The two strands of DNA are called the backbone• Each strand is made up of alternating molecules

of sugar and phosphate

DNA

• The strands are joined by molecules called nitrogen bases.

• DNA is described as a large polymer.• A polymer is made up of repeating units called

monomers.• The monomers of DNA are called nucleotides• Nucleotides are made up of a sugar,

phosphate and base.

6

DNA Nucleotide

OO=P-O O

Phosphate Group

NNitrogenous base (A, G, C, or T)

CH2

O

C1C4

C3 C2

5

Sugar(deoxyribose)

Bases

Weak hydrogen bonds hold the bases together.

8

Nitrogenous Bases• Double ring PURINES

Adenine (A)Guanine (G)

• Single ring PYRIMIDINES

Thymine (T)Cytosine (C)T or C

A or G

9

Base-Pairings• Purines only pair with

Pyrimidines• Three hydrogen bonds

required to bond Guanine & Cytosine

CG

3 H-bonds

10

T A

•Two hydrogen bonds are required to bond Adenine & Thymine

11

DNA

P

P

P

O

O

O

1

23

4

5

5

3

3

5

P

P

PO

O

O

1

2 3

4

5

5

3

5

3

G C

T A

• It is called Deoxyribose Sugar

• Deoxy means one oxygen atom less (than RNA)

• Ribose is a 5 Carbon Sugar Molecule

• The carbon atoms are numbered in a particular way from (1-5, see diagram above)

Phosphate

Functions of DNA

• Describe the functions of DNA

• DNA contains the Genetic Code (in its base sequences to make proteins).

• DNA is able to replicate itself and therefore pass on the genetic code from one generation to the next.

Antiparallel DNA

RNA

RNA stands for Ribonucleic Acid RNA is called a Nucleic Acid RNA and DNA are both involved with making proteins.

Functions of RNA

1. Together with DNA, makes proteins. 2. Contains the genetic code in some viruses

eg. HIV (these do not have DNA)

Comparison of DNA and RNA

Gene

GENE

• A gene is a section of DNA on a chromosome, that has a specific base sequence that codes for a protein.

PROTEINS

• video's for 2.7\How Genes Work Hand-Me-Down Genes Series - DNA and Proteins Part 1 - How Genes Work.wmv

Basic Gene ProteinA gene on DNA codes for a particular

protein, which, together with other compounds/molecules makes up a

characteristic eg. Eye Colour.

Name the following?

A

B

C

Ribosome

Nucleus

Cytoplasm

Cell Organelles

Cell Organelles

DNA

• http://www.youtube.com/watch?v=qy8dk5iS1f0

DNA Structure & Purpose.

• DNA is a double helix, with a phosphate-sugar backbone and bases paired by hydrogen bonds (Adenine with Thymine and Cytosine with Guanine).

• It holds the genetic code in it’s base order. DNA is found in the nucleus of eukaryotic cells

• (NB. It is also in the cytoplasm of prokaryotic cells) but eukaryotic vs Prokaryote comparisons are not needed at Level 2.

THE GENETIC CODE

Amino Acids

NUCLEIC ACIDS

• These are the biochemical macromolecules involved with the transmission of inherited information. There are two main types: DNA& RNA. Nucleic acids are polymers made up of many units called monomers.

DNA differences Similarities RNA differences

Long – many genesThymineDeoxyribose SugarStableDouble strandedIn Nucleus

Nucleic AcidsBases: Adaneine, Cytosine & Guanine. Carry Genetic code in base sequence.Have Sugar-phosphate backbones.

Short – one geneUracil.Ribose SugarLess StableSingle StrandedCan go to nucleus & Cytoplasm.

AMINO ACIDS

Redundancy vs Degeneracy

• Redundancy refers to the many ways that one Amino Acid can be coded for by various codon combinations.

• Whereas Degeneracy refers to the third position in the codon and that in most cases, if it were to change, the Amino Acid coded for would still be the same.

• Both redundancy and degeneracy protect against mutations, because most times the Amino Acid sequence and therefore protein will remain un affected.

PROTEINS

Hydrogen Bonds

Disulfide Bonds

Proteins

• Why can proteins be described as an amino acid chain and as a polypeptide chain?

• What are some of the functions of proteins?

Protein Synthesis –simple overview of mRNA and tRNA

• http://www.metacafe.com/watch/319359/human_genome/

Gene Expression outline

This unit is entitled Gene Expression. It covers some basic aspects of how the information encoded in our genome (by the order of nucleic bases), are expressed.

Remember a gene codes for a specific protein.

So the basic process of going from Gene Protein

What is needed and how it can be influenced will be covered.

Extract from Campbell & Reece

1. Copying of Genes

• This is transcription when a section of DNA is copied to RNA.

• This occurs in the nucleus.

1. Copying of Genes

What is RNA?• It is a single stranded Nucleic Acid.• Bases used (A, G, C & U instead of T)• Small & Short (one gene only)• Unstable (easily broken down & bases

recycled)

There are three types of RNA • Messenger RNA (mRNA)• Transfer RNA (tRNA)• Ribosomal RNA (rRNA)

1. Copying of Genes

Transcription:• Occurs in the Nucleus. • DNA is unzipped by Helicase• RNA Polymerase then uses the DNA as a

template to make a complementary strand of mRNA.

• Once the gene has been copied, the mRNA can then move outside the nucleus.

SEM

The banding on this chromosome is thought to correspond to groups of

genes. Regions of chromosome puffing are occur where genes are

being transcribed into mRNA.

A polytene chromosome showing localized regions that are uncoiling to expose their genes (puffing) to allow

transcription. Polytene chromosomes are giant chromosomes formed by multiple

DNA replications.

Transcription

• http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/transcription.swf

Translation

• http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/translation.swf simple

• http://207.207.4.198/pub/flash/26/transmenu_s.swf complex

Protein Synthesis

• http://www.teachersdomain.org/resources/tdc02/sci/life/gen/proteinsynth/assets/tdc02_vid_proteinsynth/tdc02_vid_proteinsynth_56_mov.html

Protein synthesis

http://www.youtube.com/watch?v=983lhh20rGY

Where & How mRNA is translated into a protein.• Translation is where the code sequence carried on the mRNA is used to create a

functional protein.• First, mRNA has to leave the nucleus via pores in the nucleus.• mRNA forms a complex with a ribosome, which is close to the nucleus (usually on

the endoplasmic reticulum). • The ribosome is an organelle, which ‘reads’ mRNA bases in a code of three bases

at a time. This is known as a codon.• tRNA brings in amino acids – there is a different kind of tRNA for each amino acid • Three unpaired bases on the tRNA are known as an anticodon. They are

complementary to a codon on the mRNA Codon–anticodon ‘matches’ combine with base pairing thus bringing the correct amino acid to the next part of the sequence.

• A start codon initiates the translation.• Peptide bonds form between amino acids building a polypeptide chain.• A stop codon ends translation. • The polypeptide chain is released from the ribosome and ‘folds’ into a three-

dimensional structure, becoming a functional protein.

2. Copying of Genes Transcription and TranslationA cell may require a particular __________(1) to be produced. They are coded by a particular sequence of bases which we call a __________(2). These code for a specific sequence of __________(3) __________(4) which form the protein. RNA differs from __________(5) in three important ways: the sugar molecules in an RNA nucleotide is __________(6), the nitrogenous base is __________(7) instead of __________(8), and the polynucleotide chain for RNA is usually __________(9). The specific gene that codes for the required protein is exposed by splitting the __________(10) bonds that holds the double __________(11) together in that region. Free RNA __________(12) bind to the __________(13) bases on the DNA strand. The sugar-phosphate __________(14) of the RNA is formed by a __________(15) reaction that occurs between the sugar of one nucleotide and the __________(16) group of another. The strand of RNA that is formed is a copy of the DNA and we call this __________(17) RNA (mRNA). The mRNA peels away from the DNA and leaves the nucleus via a __________(18) __________(19). We call this first stage of protein-synthesis __________(20). We call the next stage of protein-synthesis __________(21). Once the mRNA has left the nucleus, it attaches to a __________(22). The molecules that attach to the mRNA are called __________(23) RNA (tRNA). At one end of the tRNA molecule are __________(24) bases which we call an __________(25). On the other end of the tRNA molecule is a specific __________(26) __________(27). The distance between the __________(28) and __________(29) __________(30) is always the same. The anticodon of the tRNA binds to the complementary __________(31) on the mRNA. The tRNA brings the amino acids together into a __________(32) order. __________(33) bonds form between the amino acids and this forms the __________(34) with a specific __________(35) structure. The protein then goes on to be folded, which gives rise to the __________(36) and __________(37) structures.

Transcription and TranslationA cell may require a particular protein to be produced. They are coded by a particular sequence of bases which we call a gene. These code for a specific sequence of amino acids which form the protein. RNA differs from DNA in three important ways: the sugar molecules in an RNA nucleotide is ribose, the nitrogenous base is uracil instead of thymine, and the polynucleotide chain for RNA is usually single-stranded.

The specific gene that codes for the required protein is exposed by splitting the hydrogen bonds that holds the double helix together in that region. Free RNA nucleotides bind to the complementary bases on the DNA strand. The sugar-phosphate backbone of the RNA is formed by a condensation reaction that occurs between the sugar of one nucleotide and the phosphate group of another. The strand of RNA that is formed is a copy of the DNA and we call this messenger RNA (mRNA). The mRNA peels away from the DNA and leaves the nucleus via a nuclear pore. We call this first stage of protein-synthesis transcription.

We call the next stage of protein-synthesis translation. Once the mRNA has left the nucleus, it attaches to a ribosome. The molecules that attach to the mRNA are called transfer RNA (tRNA). At one end of the tRNA molecule are three bases which we call an anticodon. On the other end of the tRNA molecule is a specific amino acid. The distance between the anticodon and amino acid is always the same. The anticodon of the tRNA binds to the complementary bases on the mRNA. The tRNA brings the amino acids together into a specific order. Peptide bonds form between the amino acids and this forms the polypeptide with a specific primary structure. The protein then goes on to be folded, which gives rise to the secondary and tertiary structures.

Mutations

Definition

• Any permanent change to the DNA.

Since DNA carried the genetic code that has all the instructions for the normal functioning of life processes, a change to this could have significant effects on the organism.

Mutations cont.

• Mutations are the only new source of genetic information. Therefore by providing more variety in the base sequences it can eventually lead to different proteins being produced, and if the mutations is not harmful, and occurs in the gametes it can enter the gene pool providing more genetic diversity in the population.

Mutagens

• A mutagen is a physical or chemical agent that changes the genetic material, usually DNA, of an organism and thus increases the frequency of mutations above the natural background level, eg:

• radiation• toxins• Viruses

Point Mutations

• Where a base is changed through substitution, addition or deletion.

Sickle Cell Anaemia

– CH 11 – Substitution (A instead of T)– Missense Mutation.

Mutations

There are three types of point mutations1. Missense

• The change will result in a different amino acid coded for.2. Silent

• The same amino acid is coded for – the protein amino acid sequence is the same.

3. Nonsense• The change causes a stop codon to be produced; the

protein is shorter.

Ie.

Ie.

Ie.

Ie.

Ie.

FRAMESHIFTFrameshift mutations (caused by base addition or deletion) are the most detrimental. They effect every triplet and therefore codon downstream from where the mutation occurred. Therefore changing the amino acid sequence significantly.

Explain the effects of each type of mutation & how it could affect the organism it occurs in.

• Substitution mutations could have a variety of effects. They could occur and not affect the organism via a silent mutation (usually in the 3rd position of the codon) until perhaps another mutation occurs (in the 2nd or 1st position) and this changes the amino acid produced making it a missense mutation. Rarely this will be beneficial and selected for in an environment, it increases the genetic diversity of a population. Furthermore if a substitution mutation occurs to make the codon a stop codon it would be a nonsense mutation and render the gene non-functional as the full polypeptide chain would no longer be made and hence no functional protein.

• Lastly there are the addition and deletion mutations these have the most severe effects, especially if they occur towards the start of the gene. This is because a frameshift mutation will cause all the codons downstream from it to be read differently and significantly change the Amino Acid sequence coded for, so a nonfunction protein is produced.

• If the gene in which the mutation occurs produces proteins essential for life the individual will die, however if the protins produced are not essential for life the individual could live but perhaps be limited by not certain proteins produced.

Explain the effects of each type of mutation & how it could affect the organism it occurs in.

• Substitution mutations could have a variety of effects. They could occur and not affect the organism via a silent mutation (usually in the 3rd position of the codon) until perhaps another mutation occurs (in the 2nd or 1st position) and this changes the amino acid produced making it a missense mutation. Rarely this will be beneficial and selected for in an environment and increases the genetic diversity of a population. Furthermore if a substitution mutation occurs to make the codon a stop codon it would be a nonsense mutation and render the gene non-functional as the full polypeptide chain would no longer be made and hence no functional protein.

Explain the effects of each type of mutation & how it could affect the organism it occurs in.

• Lastly there are the addition and deletion mutations these have the most severe effects, especially if they occur towards the start of the gene. This is because a frameshift mutation will cause all the codons downstream from it to be read differently and significantly change the Amino Acid sequence coded for, so a nonfunction protein is produced.

Explain the effects of each type of mutation & how it could affect the organism it occurs in.

• If the gene in which the mutation occurs produces proteins essential for life the individual will die, however if the protins produced are not essential for life the individual could live but perhaps be limited by not certain proteins produced.

Redundancy & Degeneracy

Define:• Redundancy in the Genetic Code.• When some amino acids are coded for by

more than one codon. • Degeneracy in the Genetic Code.• When a change in the third position of a

codon will still code for the same Amino Acid.

• Explain how redundancy and degeneracy of the code mean that in many cases a mutation does not have an effect on the protein produced?

• The genetic code is protected against mutation by having redundancy and degeneracy built into it. Therefore if a mutation is to occur that does not cause a frameshift, it is likely that this mutation could still result in the same amino acid being coded for and therefore there is no phonotypical change for the individual.

• Degeneracy allows substation mutations that occur in the 3rd position of a codon to be (most likely) harmless. While redundancy also allows this as most Amino Acids are coded for by more than one codon, and some have different 1st position codons different but result in the same amino acid.

• So both redundancy and degeneracy minimise the effects of mutations and protect the genetic code so that the same amino acid sequence can still be produced, and life processes for that individual can still occur as normal.

Metabolic Pathways

Metabolic Pathways• http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites

/dl/free/0072437316/120070/bio09.swf::A%20Biochemical%20Pathway

Metabolic Pathway

• Definition:– A metabolic pathway is a series of biochemical

reactions that are connected by their intermediates: The reactants (or substrates) of one reaction are the products of the previous one, and so on.

• A metabolic pathway requires a series of biochemical reactions in which the product form one reaction is used as the reactant for the next. It also requires a number of enzymes to facilitate the pathway so each reaction can occur.

g

• Should any of the enzymes in the pathway be non-functional (ie, as a result from a mutation) this would cause a build up of the precursor substance (reactant) and none of the products needed further down the pathway.

g

• For example people with the condition PKU do not have a functional Phenylalanine Hydroxylase enzyme, therefore there is a build up of any Phenylaline taken in from the diet and a lacking of Tyosine (however some Tyosine can be gained from other sources). The build up of Phenylalanine caused a build up of Phenylpyruvic Acid which can cause brain damage and the conditions associated with the condition PKU. The lack of Tyrosine in their diet leads to a lack of melanin production and these individuals will also have a lighter skin colour.

Albinism

• To produce the final product melanin in which gives skin colour, there are a series of biochemical reactions that occur.

• So should the enzymes be non-function for any of these reactions, the final product of melanin will not be produced and the condition Albinism will result.

• Furthermore there will be a build-up of primary or intermediate products depending on which enzymes is unable to convert the substrate into a product.

Dominant vs Recessive Metabolic Pathways & Inheritance (1/2)

Dominant conditionIn this case both parents would have to be heterozygous for the condition otherwise it would be impossible to avoid the effect of the dominant allele.Both parents could have more than 1 point in the pathway affected so long as they were heterozygous at that point, eg Rr Rr parent 1 A--------->B---------->C Rr Rrparent 2 A--------->B---------->C rr rrOffspring A--------->B---------->C

Dominant vs Recessive Metabolic Pathways & Inheritance (2/2)

There are a number of possible combinations to the way in which a condition can be inherited because the metabolic pathway has at least two points where different genes are controlling the outcome.

Recessive conditionBoth parents have the condition so they must both have recessive alleles for one of the genes controlling one of the points of the pathway. One of their offspring can be normal because if the points which are affected in the parents are different, then each one of those can be dominated by an allele inherited from the other, Eg: rr Rr or RRparent 1 A--------->B---------->C Rr or RR rrparent 2 A--------->B---------->C Rr RrOffspring A--------->B---------->C

The Environment & Genes

• Define Environmental Factor. (Biozone: sources of genetic variation)

• Any internal or external factors that influence the expression of the genotype.

• External factors can include: temperature, light intensity, and competition. While internal factors can include: presence or absence of Hormones and/or growth factors during development.

Genotype

• Genotype is genetic constitution (the genome) of a cell or an organism.

Or • The Allele combinations an organism has at a

particular locus.

Environment & Genotype

• Environmental mutagens can affect genotype for the next generation should the mutation occur in the gametes.

Explain how the environment can affect the genotype, give specific examples. • The environment can effect genotype via mutagenic agents

increasing the likelihood of mutations to occur. If the mutation causes a change in the protein, it becomes a new allele and can change the genotype for some cells in that individual, and if the mutation occurred in the gametic cells the new allele can enter the gene pool.

• For example those who smoke may develop lung cancer, which affects the lung cells in the body as they have come into contact with the mutagen, however if the cancer spread and the poisonous chemicals breathed in from tobacco smoking caused a mutation to occur in that individuals gametes that caused a new allele, then their offspring can be affected and have the new allele in every cell of their body.

Temperature & Phenotype

• Dark pigment produced only in cooler parts of the body.

• Ie. Ice pack on Himalayan rabbit = Black Hair.

Explain how the environment can affect the phenotype, give specific examples. • The environment can affect the way the genes are expressed

without changing the alleles or genotype of an individual. For example if someone were to plant tall beans that say the grow over 2 meters tall but, fail to water them regularly, space them out and weed the soil around them, the plants may be stunted in their growth through lack of water, nutrients and sunlight availability.

• Another example could be human skin colour, if there were identical twins with light skin colour, but one twin did a lot of sport and work outside while the other was mainly indoors, then the outdoor twin would build up more of a tan and melanin in their skin as protection against the sun’s rays and therefore look different than their twin.

Epigenetics

http://www.youtube.com/watch?v=LcaRTDsLmiA

EpigeneticsLife Processes Pgs. 229-231.Define Epigenetics• The study of the factors that activate and

silence gene expression.• Epi means ‘in addition too’, therefor the

study of epigenetics is looking at the factors that affect an individual in addition to normal genetics.

Agouti Gene

• http://learn.genetics.utah.edu/content/epigenetics/nutrition/

Explain how these above example of ‘Agouti’ mice can be genetically identical and yet look so different.• The Agouti Mice from the example have ideantical DNA, but

different epigenomes. This means that agouti gene is silenced in one mouse (small brown) while it is expressed in the other mouse (large yellow).

• The expression of the Agouti gene is linked with various methylation sources. So while the mice were developing in the womb, if the diet of the mother was high in methyl groups, it caused the agouti gene so be methylated and therefore silenced, giving a slim, healthy brown mouse.

• While if the mothers diet was low in methyl groups, then the Agouti gene would be expressed resulting in the mouse being obese, prone to cancer and diabetes and yellow in coat colour. This explains why the appearance can be so different while the gene’s still identical.

What is the significance of DNA methylation? What effect does this have on Gene Expression?

• DNA methylation determines if the genes are expressed or silenced. When DNA is methylated it is tightly coiled up and cannot be unwound for protein synthesis, therefore the gene is not expressed. Gene silencing can have significant effects as the protein produced from on gene can change the balance of a metabolic pathway and prevent various products being made and cause a build-up of some precursors.

The Bible & Epigenetics• Daniel 1:1-21• New International Version (NIV)• Daniel’s Training in Babylon• 1 In the third year of the reign of Jehoiakim king of Judah, Nebuchadnezzar king of

Babylon came to Jerusalem and besieged it. 2 And the Lord delivered Jehoiakim king of Judah into his hand, along with some of the articles from the temple of God. These he carried off to the temple of his god in Babylonia[a] and put in the treasure house of his god.

• 3 Then the king ordered Ashpenaz, chief of his court officials, to bring into the king’s service some of the Israelites from the royal family and the nobility— 4 young men without any physical defect, handsome, showing aptitude for every kind of learning, well informed, quick to understand, and qualified to serve in the king’s palace. He was to teach them the language and literature of the Babylonians.[b] 5 The king assigned them a daily amount of food and wine from the king’s table. They were to be trained for three years, and after that they were to enter the king’s service.

• 6 Among those who were chosen were some from Judah: Daniel, Hananiah, Mishael and Azariah. 7 The chief official gave them new names: to Daniel, the name Belteshazzar; to Hananiah, Shadrach; to Mishael, Meshach; and to Azariah, Abednego.

• 8 But Daniel resolved not to defile himself with the royal food and wine, and he asked the chief official for permission not to defile himself this way. 9 Now God had caused the official to show favor and compassion to Daniel, 10 but the official told Daniel, “I am afraid of my lord the king, who has assigned your[c] food and drink. Why should he see you looking worse than the other young men your age? The king would then have my head because of you.”

• 11 Daniel then said to the guard whom the chief official had appointed over Daniel, Hananiah, Mishael and Azariah, 12 “Please test your servants for ten days: Give us nothing but vegetables to eat and water to drink. 13 Then compare our appearance with that of the young men who eat the royal food, and treat your servants in accordance with what you see.” 14 So he agreed to this and tested them for ten days.

• 15 At the end of the ten days they looked healthier and better nourished than any of the young men who ate the royal food. 16 So the guard took away their choice food and the wine they were to drink and gave them vegetables instead.

• 17 To these four young men God gave knowledge and understanding of all kinds of literature and learning. And Daniel could understand visions and dreams of all kinds.

• 18 At the end of the time set by the king to bring them into his service, the chief official presented them to Nebuchadnezzar. 19 The king talked with them, and he found none equal to Daniel, Hananiah, Mishael and Azariah; so they entered the king’s service. 20 In every matter of wisdom and understanding about which the king questioned them, he found them ten times better than all the magicians and enchanters in his whole kingdom.

• 21 And Daniel remained there until the first year of King Cyrus.

The Bible & Epigenetics• Genesis 30:37-40 (NIV)• 37 Jacob, however, took fresh-cut branches from poplar,

almond and plane trees and made white stripes on them by peeling the bark and exposing the white inner wood of the branches. 38 Then he placed the peeled branches in all the watering troughs, so that they would be directly in front of the flocks when they came to drink. When the flocks were in heat and came to drink, 39 they mated in front of the branches. And they bore young that were streaked or speckled or spotted. 40 Jacob set apart the young of the flock by themselves, but made the rest face the streaked and dark-colored animals that belonged to Laban. Thus he made separate flocks for himself and did not put them with Laban’s animals.

The Bible & Epigenetics

• Proverbs 23:7• King James Version (KJV)• 7 For as he thinketh in his heart, so is he: Eat

and drink, saith he to thee; but his heart is not with thee.

The Bible & Epigenetics

• Romans 12:2• New International Version (NIV)• 2 Do not conform to the pattern of this world,

but be transformed by the renewing of your mind. Then you will be able to test and approve what God’s will is—his good, pleasing and perfect will.

• http://jbq.jewishbible.org/assets/Uploads/364/364_sheep.pdf

EXTRA ACTIVITIES

• The base sequence can be used to make up the amino acid chain. Can this be done in the reverse, having an amino acid chain translated back into RNA and reverse Transcribed into the same DNA that coded for it? Explain your answer.

• No it cannot give the same DNA that coded for the Amino Acid sequence. This is because there are many codons that code for an amino acid, therefore there is no way of ensuring that a DNA sequence produced is the same as the original due to redundancy and degeneracy in the genetic code.

(c) Describes how mRNA is processed.

Eg non coding regions / introns are removed.

Explains how mRNA is processed.

Eg mRNA / Primary transcript produced by transcription has both coding regions / exons and non-coding regions / introns of RNA. These non coding regions / introns are removed to leave only the coding regions / exons.

CGA TCA GCT ACC TCT

GCU AGU CGA UGG AGA

ala ser arg trp arg

Achievement Achievement with Merit Achievement with Excellence

Any TWO of:• Transcription is described.

Eg: Production of mRNA copy of DNA / genetic material 

• Translation is described.E.g. information from mRNA is used to join amino acids into a polypeptide. 

• A role of RNA is described.

Eg: mRNA carries the code from a gene to / site of synthesis / ribosome. Eg: tRNA carries an amino acid which connects with the codon of mRNA at the ribosome.

Any TWO of:• Explains the roles of

transcription.Eg: Transcription is the process where mRNA is manufactured by attaching free nucleotides to complementary DNA strand. 

• Explains the role of translation.Eg: Translation is the process happening at the ribosome, where RNA codons are matched with tRNA anti codons, resulting in the joining of amino acids. Each amino acid is specific to an anticodon / codon.  

• Explains a link between amino acids and protein folding

Eg: The interactions between amino acids sequence can affect the final shape / folding of the protein.  

Discusses how DNA sequence results in the formation of a protein.

Eg: During transcription, mRNA is produced through complementary base pairing with exposed bases on DNA. mRNA is read via translation at the site of the ribosome (rRNA), where codon sequences are translated via tRNA into a chain of amino acids. tRNA attach to specific amino acids and contain an anti codon, complementary to the codons of the mRNA.

AND

The final protein / order in which the amino acids are joined is a result of the DNA sequence / genetic code.

OR

The order of amino acids affects the folding of the protein structure due to the interactions between them. Sulfur bridges / bonds between cysteines / hydrophobic / hydrophilic interactions / will lead to folding of the polypeptide / protein chain.