DNA and RNA

Chapter 12

DNA

Section 12-1

DNA – Griffith and Transformation

• Frederick Griffith –

bacteriologist studying how

certain types of bacteria

produce pneumonia

– Isolated 2 strains of

pneumonia from mice

• Smooth(S) disease causing

strain and Rough(R)

harmless strain

– Injected heated (heat-killed) Disease causing strain into mice

• didn’t cause pneumonia

– Combined harmless strain and heat-killed disease causing strain and injected into mice

• caused pneumonia

DNA – Griffith and Transformation

• Transformation – the two types injected

together caused the mice to die! Some

transformation had to take place for the

harmless bacteria to change into the deadly

pneumonia-causing strain!

– The heat killed bacteria had passed their disease

causing ability to the harmless strain!

– Concluded that some factor had to be transferred

between the two strains of bacteria – something

that heat did not kill!

• And the offspring of the transformed bacteria also had

this factor so he suspected that the factor may be a

gene

DNA – Avery and DNA

• Oswald Avery repeated the experiment but

isolated the factor that transmitted the

disease causing ability

– Treated bacteria with specific enzymes to destroy

only certain parts of the bacteria (proteins, RNA,

etc)

• Only bacteria whose DNA had been destroyed failed to

transmit the disease causing ability

• Showed that DNA was the source of this transformation

DNA - Hershey-Chase Experiment

• Martha Chase and Alfred Hershey

discovered that DNA stores and transmits

genetic information

– Did so by studying bacteriophages (viruses that

attack bacteria)

– These viruses are

comprised of a

DNA center and a

protein coat

DNA - Hershey-Chase Experiment

– How do bacteriophages work?

DNA - Hershey-Chase Experiment

– Radioactive Marker Experiment

• Used radioactive substance as markers in

bacteriophages

– Protein coat – Sulfur-35 (35S)

– DNA core – Phosphorous-32 (32P)

• “Marked” bacteriophages and bacteria were mixed

together and they waited for the virus to inject their

genetic material

– Bacteria were then tested for radioactivity

– The type of radioactivity detected would tell Chase and

Hershey which part of the bacteriophage was transmitting

information

– Nearly all was from 32P marker in DNA not

protein coat

DNA - Hershey-Chase Experiment

DNA – Activity

• Genes are made of DNA, a large, complex molecule. DNA is composed of individual units called nucleotides. Three of these units form a code. The order, or sequence, of a code and the type of code determine the meaning of the message.

– 1. On a sheet of paper, write the word cats. List the letters or units that make up the word cats.

– 2. Try rearranging the units to form other words. Remember that each new word can have only three units. Write each word on your paper, and then add a definition for each word.

– 3. Did any of the codes you formed have the same meaning?

– 4. How do you think changing the order of the nucleotides in the DNA codon changes the codon’s message?

DNA – Video on DNA and Genes

DNA –The Components and

Structure of DNA • DNA – (Deoxyribonucleic acid) is made of units

called nucleotides

• Nucleotides – 3 basic components – Deoxyribose – 5-carbon sugar

– Phosphate group

– Nitrogen bases • Adenine (a purine)

• Guanine (a purine)

• Cytosine (a pyrimidine)

• Thymine (a pyrimidine)

– Complementary Pairing – Base Pairing rules:

• Adenine Thymine

• Cytosine Guanine

– Sequence of one strand determines sequence of other

Adenine Guanine Cytosine Thymine

Phosphate

group Deoxyribose

DNA –The Components and

Structure of DNA • The “backbone” of DNA is the sugar and phosphate

groups (deoxyribose and the phosphate group) of each nucleotide.

• The nitrogenous bases stick out like a staircase tread (sideways) from this backbone

• Nucleotides can be joined in any sequence – Several nucleotides together make

a gene

– But scientists were still puzzled about how this string could carry genetic information (weren’t there other molecules that were strung together?) So there had to be more to DNA’s structure

Adenine Guanine Cytosine Thymine

Phosphate

group Deoxyribose

DNA –The Components and

Structure of DNA • Chargaff’s Rules

– Erwin Chargaff noted that regardless of species, or even kingdom, DNA bases always appeared in the same proportions as each other

– Concluded that bases are paired: • [A = T]

• [G = C]

– But why?

• X-Ray evidence – Rosalind Franklin used x-rays to

study the structure of DNA

– Looked at how the x-rays scattered on the film

• From the X shaped pattern, she concluded that DNA was twisted in a coil-like shape (a helix), that there may be two strands, and that the nitrogenous bases were near the center

Adenine Guanine Cytosine Thymine

Phosphate

group Deoxyribose

Nucleotide

Hydrogen

bonds

Sugar-

phosphate

backbone

DNA –The Components and

Structure of DNA

• The Double Helix

– Francis Crick and James Watson also working on DNA

structure

– Saw work of Rosalind Franklin

and used it to build a structural

model of DNA

• A double helix

• Hydrogen bonds hold

strands together at

nitrogenous bases

CHROMOSOMES AND DNA

DUPLICATION

Section 12-2

Chromosomes and DNA Replication

– Chromosome Structure

• Chromatin – Consists of DNA tightly coiled around proteins called Histones

– Histones – forms nucleosome (believed to help in separating chromosomes in mitosis)

• Coiled and super-coiled to form chromosomes

Chromosome

Supercoils

Coils

Nucleosome

Histones

DNA

double

helix

• 4 million base-pairs

per cell (in both

prokaryotic and

eukaryotic cells)

• More than a meter

long in humans

DNA Replication

• DNA Replication – the process in which DNA strands and duplicate strands are produced – Results in two DNA Molecules each with one new

strand and one original strand

• The DNA strands separate at areas along the chromosome called replication forks – In most prokaryotes this is a single point

– In larger eukaryotic chromosomes, this may be hundreds of points

• DNA polymerase – an enzyme that joins DNA nucleotides to the opened parent strands

• Two complimentary strands are produced according to base-pairing rules

• A DNA strand that has the bases CTAGGT produces a strand with the bases? _ _ _ _ _ _

DNA Replication

Replication

fork

DNA

polymerase

New strand

Original

strand DNA

polymerase

Nitrogenous

bases

Replication

fork

Original

strand

New strand

Growth

Growth

DNA Replication

• Enzymes (DNA polymerase) “unzip” the DNA strand by

breaking the hydrogen bonds

• Also allows for “proofreading” what has been produced

so that DNA is replicated with near 100% accuracy

DNA Replication

• Short videos on DNA Replication

– DNA replication animation by interact Medical –

YouTube

• http://www.youtube.com/watch?v=zdDkiRw1PdU&featur

e=related

– DNA replication (6 10) – YouTube

• http://www.youtube.com/watch?v=z685FFqmrpo&featur

e=channel

http://www.youtube.com/watch?v=zdDkiRw1PdU&feature=relatedhttp://www.youtube.com/watch?v=zdDkiRw1PdU&feature=relatedhttp://www.youtube.com/watch?v=zdDkiRw1PdU&feature=relatedhttp://www.youtube.com/watch?v=z685FFqmrpo&feature=channelhttp://www.youtube.com/watch?v=z685FFqmrpo&feature=channelhttp://www.youtube.com/watch?v=z685FFqmrpo&feature=channel

DNA Replication relating to Cell

Reproduction

RNA AND PROTEIN SYNTHESIS

Section 12-3

RNA and Protein Synthesis

• Structure of RNA

– Similarities:

• Made up of a chain of nucleotides (like DNA)

• Has a phosphate group, a 5-carbon sugar and a

nitrogenous base

– Differences

• Sugar is ribose (not deoxyribose)

• RNA is single stranded (not a double helix)

• Contains uracil instead of thymine

– Often just a segment that corresponds to a

segment of DNA – often a single gene

RNA and Protein Synthesis

• General Functions of RNA

– It can be varied but is generally protein synthesis

• Types and functions of RNA

– Messenger RNA (mRNA)

• Carries copies of the genetic instructions for assembling

amino acids into proteins

• Serve as messengers from DNA to the rest of the cell

– Ribosomal RNA (rRNA)

• Part of the structure of ribosomes (where proteins are

actually made)

– Transfer RNA (tRNA)

• Transfers each amino acid to the ribosomes as it is

specified in the instructions provided by mRNA

RNA and Protein Synthesis

• Transcription

– The process of producing RNA from a sequence

of DNA molecule

– Requires an enzyme called RNA polymerase

(very similar to DNA polymerase)

• Separates the DNA strands then uses one strand of

DNA to assemble nucleotides to form the single

stranded RNA molecule which separates and then DNA

is rejoined.

RNA and Protein Synthesis

• Transcription Process

– RNA polymerase only binds to

specific regions called promoters

(have specific base sequences) –

also provides signals for when to

stop

– RNA polymerase separates DNA

by breaking the hydrogen bonds

– RNA nucleotides are assembled

according to base pairing rules:

• (G – C) Guanine to Cytosine

• (A – U) Adenine to Uracil

RNA and Protein Synthesis

• Transcription

Process

– Begins at a

promoter

region (a

section of

DNA with

a specific

sequence

– Similar

process to end

Adenine (DNA and RNA)

Cystosine (DNA and RNA)

Guanine(DNA and RNA)

Thymine (DNA only)

Uracil (RNA only)

RNA polymerase

RNA DNA

RNA and Protein Synthesis

• RNA Editing

– Makes RNA molecule “functional”

– Most DNA are not involved in coding for proteins

but get transcribed anyway

• “Non-coding” segments of RNA must be removed

• Introns – non-coding regions

– Coding segments of RNA are spliced together

• Exons – coding regions; instructions to make proteins

– All this editing takes place inside the nucleus

before the mRNA heads out for the ribosomes

RNA and Protein Synthesis

• The Genetic Code

– Translates mRNA

“language” into

proteins (amino acids)

– Codon – 3 nucleotide

sequence that

specifies for a single

amino acid

– Sample RNA

sequence: AUG UCG

CAC GGU UAG

• What amino acid

sequence will the

above RNA sequence

produce?

RNA and Protein Synthesis

• The Genetic Code

– Sample RNA

sequence: AUG UCG

CAC GGU UAG

• What 5-protein

sequence will the above

RNA sequence

produce?

– ANSWER:

• Methionine-Serine-

Histidine-Glycine-Stop

– **NOTE – AUG can be

a “start” sequence or

Methionine; most

proteins begin with the

amino acid Methionine

RNA and Protein Synthesis

• Translation

– The process of decoding an mRNA message into a

protein (a polypeptide chain)

– Takes place on the ribosomes

– Process

• Begins when mRNA attaches to a ribosome

• As each codon moves through the ribosome, the correct amino

acid is brought by tRNA

– tRNA only carries one amino acid (corresponding to one codon)

– tRNA also has 3 unpaired bases called an anticodon (corresponding

to the codon that the tRNA is supposed to attach to)

• Amino acids are joined together into long chains in the ribosome

• Continues until a “stop” codon is reached (there are several)

RNA and Protein Synthesis -

Translation

RNA and Protein Synthesis –

Translation (continued)

RNA and Protein Synthesis

from to to make up

RNA Concept Map

also called which functions to also called also called which functions to which functions to

can be

RNA

Messenger RNA Ribosomal RNA Transfer RNA

mRNA Carry instructions rRNA Combine

with proteins tRNA

Bring

amino acids to

ribosome

DNA Ribosome Ribosomes

MUTATIONS

Section 12-4

Mutations - Activity

1. Copy the following information about Protein X: Methionine—Phenylalanine—Tryptophan—Asparagine—Isoleucine—STOP.

2. Use Figure 12–17 on page 303 in your textbook to determine one possible sequence of RNA to code for this information. Write this code below the description of Protein X. Below this, write the DNA code that would produce this RNA sequence.

3. Now, cause a mutation in the gene sequence that you just determined by deleting the fourth base in the DNA sequence. Write this new sequence.

4. Write the new RNA sequence that would be produced. Below that, write the amino acid sequence that would result from this mutation in your gene. Call this Protein Y.

5. Did this single deletion cause much change in your protein?

Explain your answer.

Mutations

• DNA contains the code of instructions for

cells. Sometimes, an error occurs when the

code is copied. Such errors are called

mutations.

• Two main types

– Gene mutations

• Changes in one or just a few nucleotides at a single

point in the DNA sequence

– Chromosomal mutations

• Changes in the number or structure of chromosomes

• May even change the location of genes on the

chromosomes or the number of copies of the genes

Mutations

• Gene Mutations

– Caused by errors in replication

– Changes in DNA affect the amino acid sequence

– Point mutations – occur at a single point in the

DNA sequence

– Substitutions – one base is changed into another

• Usually affects one amino acid in the protein

– Insertions and Deletions – a base is inserted or

removed from the DNA sequence

• Causes frameshift mutations

• The “reading frame” of the genetic message is shifted and

chances every amino acid that follows the point of the

mutation

Mutations

Substitution Insertion Deletion

Section 12-4

Gene Mutations: Substitution,

Insertion, and Deletion

Mutations

Mutations

• Chromosomal Mutations – Changes the structure of chromosomes by changing

the location or the number of genes on a chromosome

– Deletions – the loss of all or part of a chromosome

– Duplications – produce extra copies of parts of a chromosome

– Inversions – Reverse the direction of parts of chromosomes

– Translocations – part of one chromosome breaks off and attaches to another

Deletion

Duplication

Inversion

Translocation

Chromosomal Mutations Section 12-4

Chromosomal Mutations

Mutations

• Significance of Mutations

– Most mutations are neutral – have little or no

effect on the expression of genes or the coding of

proteins

– Dramatic changes can cause harmful results

• Genetic disorders (Chapter 14)

• Disruption of normal biological activities

• Cancer (many kinds)

• Some may even be incompatible with life!

– Also the source of genetic variability and

adaptation to new or changing environments

• Galapagos Island finches and beak size

GENE REGULATION

Section 12-5

Gene Regulation

• If a specific kind of protein is not continually used the gene for that protein can be turned “off” – Repressor Proteins – bind to the chromosome to block

transcription from occurring (common in prokaryotic cells)

• Operon – a group of genes that operate together

• Example: – Lac operon in E. coli – group of genes that code for proteins

that breakdown lactose (lactase)

– Lac repressor –

• Protein that bind to chromosome to block transcription of lac operon

• “turn off” the lac genes when lactose isn’t present

Gene Regulation

• Eukaryotic Gene Regulation – Operons are not usually found in eukaryotic cells

• Most genes are controlled individually with more complex regulatory sequences than operons

– Many eukaryotic genes have a sequence of TATATA or TATAAA before the start of transcription

• Called a “TATA box”

• Promoters are usually found just before this spot

– Many different proteins can bind to these enhancer sequences resulting in very complex gene regulation for eukaryotes

Gene Regulation

• Eukaryotic Gene Regulation (continued) – Allows for cell specialization

• All cells have a specific function for the body – Nerve cell genes are not expressed in liver cells

– Specialized cells: • regulate the expression of its genes

• only need to express genes it uses to function

– Areas of chromosome that help to regulate gene expression in Eukaryotes:

• Enhancer Sequence – Opening tightly packed chromatin

– Attract RNA polymerase

– Can act as a repressor to block transcription

• Promoter Sequence – a spot for RNA polymerase to bind to start transcription

• “TATA Box” - helps position RNA polymerase for transcription

Gene Regulation

• Development and Differentiation – All cells in developing embryo undergo differentiation

• Cells become specialized in structure and function

– Hox Genes – • control the development and differentiation by “telling”

cells how they should differentiate as the body develops

• Determine an animal’s basic body plan

– Hox genes – expressed like cascade affect • Genes for head formation – toward one end of chromosome

• Genes for posterior body parts – at other end of chromosome

– Hox genes are turned on in precise order • Genes for anterior formation get turned on first and then

genes for development of posterior formations are turned on

Gene Regulation

• Development and

Differentiation

– No mutations

normally occur on

Hox Genes

• Often lethal

– When mutations do

occur

• Change the organs

and body segments

during development

Gene Regulation

• Development and

Differentiation

– No mutations normally

occur on Hox Genes

• Often lethal

– When mutations do occur

• Change the organs and

body segments during

development