Semester 2: Unit 1:

Molecular Genetics

Information “Overload”:

• Cells store information in DNA.• Information is used to build molecules

needed for cell growth. • As cell size increases, the demands on that

information (DNA) grow too.

Exchanging Materials:

• Food, oxygen, & water enter a cell through the cell membrane.

• Waste products leave the same way.

• The rate of exchange depends on the surface area of a cell.

• The rate at which nutrients are used up & waste products are produced depends on the cell’s volume.

• In multicellular organisms:

-cell division leads to growth

-allows organisms to repair & maintain its body

• In single-celled organisms:

-cell division is a form of reproduction

•Before a cell grows too large, it divides into 2 new daughter cells= cell division.

•Before cell division, the cell copies all of its DNA so that each new cell receives a complete set of DNA

•Chromatin- long strands of DNA wrapped around

protein*genetic material of a non-dividing cell

• Chromosomes- short, thick coiled up strands of DNA and protein

*genetic material of a dividing cell

• Homologous chromosomes-

matching or corresponding chromosomes;

*one from each parent; in diploid cells

• Mitosis- cell division that maintains the number of chromosomes to produce somatic (body) cells.

*responsible for growth in multicellular organisms

*produces diploid cells- cells with the same number of chromosomes as the ordinal parent cell

2n= 2 sets of chromosomes

• Meiosis- cell division that reduces the number of chromosomes by half to produce gametes- sex cells

*prodcues haploid cells- cells with half the number of chromosomes as the original parent cell

n = 1 set of chromosomes

Sexual Reproduction:

•offspring are produced by the fusion of 2 sex cells (sperm & egg unite = fertilization )– 1 from each of 2 parents.

• fuse into a new single dipolid cell (zygote)

• the offspring grows by cell division

•offspring inherit DNA from both parents.

• carried out by animals & plants, & a few one-celled organisms

• Cancer cells do not respond to signals that regulate growth and therefore divide uncontrollably.

• Cancer is a disorder in which body cells lose the ability to control cell growth.

• Cancer cells divide uncontrollably to form a mass of cells called a tumor.

• Cancers are caused by defects in genes that regulate cell growth & division.

• Some sources of gene defects are:

-smoking tobacco

-radiation exposure

-defective genes

-viral infection

• A benign tumor is noncancerous.

-does not spread to surrounding healthy tissue.

• A malignant tumor is cancerous.

-invades & destroys surrounding healthy tissue

-can spread to other parts of the body.

• The spread of cancer cells- metastasis

• Cancer cells:

-absorb nutrients needed by other cells

-block nerve connections

-prevent organs from functioning.

• DNA -a nucleic acid made of nucleotides joined into strands/chains by covalent bonds.

• DNA= Deoxyribonucleic Acid• Each DNA nucleotide is made of 3 parts:

1-Deoxyribose sugar2-Phosphate group (PO4)3-Nitrogenous base (1 of 4):

purines: Adenine(A), Guanine(G) (2 rings) pyrimidines: Cytosine(C), Thymine(T) (1 ring)

• The DNA that makes up genes must:

1-store information- instructions that cause a cell to develop

2-copy information- the structure of DNA (its H Bonds) is the key to how it being copied

3-transmit the genetic info- passing on critical info in DNA to new daughter cella.

•Nucleotides join by covalent bonds between their sugar & phosphate groups.• nitrogenous bases stick out sideways from the

chain• nucleotides can join together in any order

•Chargaff’s rules:

amount of [A] = amount of [T]

amount of [G] = amount of [C]• Rosalind Franklin revealed an X-shaped pattern

showing 2 strands in DNA twist around each other.

*Also suggested the bases are near the center

Watson & Crick- The Double-Helix Model:

•build a 3-D model that explained the structure & properties of DNA•model was a double helix- two strands wound around

each other like a twisted ladder• explains Chargaff’s rules• accounted for Franklin’s X-ray pattern• the 2 strands of DNA are “antiparallel”- they run in

opposite directions•bases to come in contact at center• each strand carries a series of nucleotides

• Watson & Crick discovered that hydrogen bonds form between certain bases in the center of the molecule, holding the 2 DNA strands together

• H bonds are weak chemical forces that allow the 2 strands of the helix to separate and rejoin which is critical to DNA replication

• H bonds would form only between base pairs- A with T, & G with C (base pairing).

• Watson & Crick realized base pairing explained Chargaff’s rule, told why the # of [A]=[T] & [G]=[C].

12.2- The Structure of DNA

Hydrogen Bonding:

2 hydrogen bonds

between A and T

3 hydrogen bonds

between G and C

12.2- The Structure of DNA

DNA Double Helix:

2 strands need

to TWIST

around

each other.

• Before a cell divides, it duplicates its DNA in a copying process called replication.

The Replication Process:

• Results in 2 DNA molecules identical to each other with each molecule having 1 original strand & 1 new strand

12.3- DNA ReplicationThe Replication Process:

1. Untwist the DNA molecule2. Unzip the two strands of the double

helix-separate by breaking the H bonds between the base pairs.

3. 2 replications forks allow complimentary bases to be brought in following the rules of base pairing

4. Rezip- new H bonds formed5. Retwist BOTH DNA molecules

12.3- DNA ReplicationThe Role of Enzymes:

• Helicase- untwists & unzips the DNA• The principal enzyme involved in DNA

replication is DNA polymerase.*Has 2 jobs:

• joins individual nucleotides to produce a new strand of DNA.

• also “proofreads” each new DNA strand, making sure that each molecule is an exact copy of the original.

12.3- DNA Replication

In eukaryotic cells,

replication begins at

many places on the DNA

molecule, proceeding in

both directions until each

chromosome is copied.

13.1- RNA

RNA- Ribonucleic Acid

- a long chain of nucleotides

- uses the base sequence copied from DNA to direct the production of proteins

13.1- RNA

Comparing RNA and DNA :

DNA vs. RNA

Deoxyribose sugar ribose sugar

Double-stranded single-stranded

Thymine base uracil base

In nucleus nucleus & cytoplasm

“master plan” “blue print”

*both contain phosphate groups & the bases A, G, and C

The three main types of RNA:messenger RNA (mRNA)ribosomal RNA (rRNA)transfer RNA (tRNA)

• involved in protein synthesis; each has a specific role

• controls the assembly of amino acids into proteins.

13.1- RNA

Messenger RNA:

• carry information from DNA to other parts of the cell

• carry copies of instructions for assembling amino acids into proteins

Ribosomal RNA:

•make up ribosomes along with proteins

•Ribosomes- the sites where proteins

are assembled.

Transfer RNA:• transfers each amino acid to the

ribosome as it is specified by coded messages in mRNA

RNA Synthesis:• transcription- creating mRNA from DNA• segments of DNA serve as templates to

produce complementary RNA molecules•Prokaryotes- RNA synthesis & protein

synthesis occur in the cytoplasm. • Eukaryotes- RNA is produced in the

nucleus & then moves to the cytoplasm to play a role in the production of proteins.

13.1- RNA

Transcription:

•RNA polymerase- uses 1 strand of DNA as a template to assemble nucleotides into a complementary strand of mRNA

•RNA polymerase binds only to promoters-regions of DNA that show RNA polymerase exactly where to begin making RNA.

13.1- RNA

Transcription:

1. Unwind & unzip DNA

2. Promoter binds RNA

polymerase on DNA

3. RNA polymerase uses 1

DNA strand to make RNA

4. mRNA breaks away &

leaves nucleus

5. Rezip & rewind DNA

13.2- Ribosomes & Protein Synthesis

•Proteins are made by joining amino acids together into long chains- polypeptides.

•20 different amino acids in polypeptides

•RNA contains bases: A, C, G, & uracil (U).

• These bases form a “language,” or genetic code, with just 4 “letters”: A, C, G, and U.

13.2- Ribosomes & Protein Synthesis

The Genetic Code:• Each three-letter “word” in mRNA is

known as a codon. • A codon consists of 3 RNA bases that

specify 1 amino acid to be added to the polypeptide chain.

13.2- Ribosomes & Protein Synthesis

• 4 different bases in RNA, there are 64 possible 3-base codons (4 × 4 × 4 = 64).

• Most amino acids can be specified by more than 1 codon.

• Methionine, AUG, is the “start” codon for protein synthesis

• mRNA is read 3 bases at a time until a “stop” codon is reached ending translation

13.2- Ribosomes & Protein Synthesis

AUG=start

UGA=stop

UAA=stop

UAG= stop

Pg. 367 in

textbook

13.2- Ribosomes & Protein Synthesis

Translation:

• sequence of bases in mRNA= instructions of the order of amino acids joining to form a polypeptide

•Proteins formed from polypeptide chains

•Ribosomes assemble amino acids into polypeptide chains.

•decoding of an mRNA message into a protein is translation.

13.2- Ribosomes & Protein Synthesis

Steps in Translation:

1- mRNA is transcribed in the nucleus & enters the cytoplasm

2- a ribosome attaches to mRNA

3- ribosome reads each mRNA codon & directs tRNA to bring specific amino acid to the ribosome

4- ribosome attaches amino acid to chain

13.2- Ribosomes & Protein Synthesis

Steps in Translation:

Step 1

Step 2

Step 3

Step 4

13.2- Ribosomes & Protein SynthesistRNA:

• each tRNA carries 1 kind of amino acid• each tRNA molecule has 3 unpaired

bases- anticodon- is complementary to the mRNA codon.

Ex: anticodon UAC pair with the codon AUG

13.2- Ribosomes & Protein Synthesis

•Ribosome forms a peptide bond between the amino acids• bond holding the first tRNA molecule to

its amino acid is broken; tRNA leaves• ribosome moves down to next codon,

and tRNA brings in amino acid specified by the codon

13.2- Ribosomes & Protein Synthesis

• polypeptide chain grows until a stopcodon is reached

• ribosome releases the polypeptide & the mRNA molecule, completing translation

•Mutations- heritable changes in genetic info (DNA)

•Cells may make mistakes copying DNA

Gene Mutations:• point mutations- involve changes in 1 or a few

nucleotides • occur at a single point in the DNA sequence

• If a gene in 1 cell is altered, it can be passed on to every developing cell.

• Types: substitutions, insertions, deletions

Substitutions- 1 base is changed to a different base• affect only 1 amino acid or NO effect.

13.3- Mutations

Gene Mutations:

Insertions- 1 base is inserted (added) into the DNA sequence.

Deletions- 1 base is removed from the DNA sequence.

13.3- Mutations

Gene Mutations:

Insertions & Deletions result in frameshiftmutations

• shift the “reading frame” of the genetic message- read 3 bases at a time, but shifts every codon that follows the mutation

• can change every amino acid that follows the point of the mutation, & alter a protein that its unable to perform its function.

13.3- Mutations

Chromosomal Mutations:Deletion- involves the loss of all or part

of a chromosome.

*Part B of the chromosome is lost or deleted

13.3- MutationsChromosomal Mutations:

Duplication- produces an extra copy of all or part of a chromosome

*Part B was doubled and added in to chromosome

13.3- MutationsChromosomal Mutations:

Inversion- reverses the direction of parts of a chromosome.

*parts B and C were reversed or flip-flopped

13.3- MutationsChromosomal Mutations:Translocation- occurs when part of one

chromosome breaks off and attaches to another.

*Part GH is added in from another chromosome

13.3- Mutations

Effects of Mutations:

• Mutagens- chemical or physical agents in the environment that cause mutations

• Chemical: certain pesticides, tobacco smoke, & environmental pollutants

• Physical: X-rays & ultraviolet light

• Effects of mutations on genes vary:

-little or no effect on organism

-beneficial- resist pesticides; polyploid crops

-negative- cancer or disease