Genetics Exam 3

What is the one gene-one enzyme hypothesis?

Each gene controls production of a single enzyme.

What evidence in Beadle and Tatum’s experiment supported the one gene-one enzyme hypothesis?

They isolated mutant strains of N. crassa after X-ray- the mutant strains were blocked at a particular step in the biosynthesis pathway.

What are the major steps of protein synthesis?

Transcription (DNA becomes mRNA), RNA processing (splicing, 5’ capping, polydenylation), Translation (mRNA becomes protein), Post translational modifications (folding, phosphorylation)

What is the role of the ribosome in protein synthesis?

Initiate translation

How do ribosomes intimate translation in eukaryotes?

The small subunit binds to the 5’ end cap of mRNA with help from initiiation factors

How do ribosomes start translation in prokaryotes?

They bind the small subunits to the Shine-Dalgarno sequence of the mRNA

What do the small subunits of ribosomes do?

bind to mRNA and help align tRNA during translation

What do the large subunits of a ribosome do?

Catalyze the formation of peptide bonds between amino acids

The E-site of a ribosome

where tRNA leaves after donating their amino acid (EXIT)

The P site of a ribosome

holds the growing polypeptide chain (PEPTIDYL)

The A site of a ribosome

Holds incoming tRNA carrying amino acids (AMINOACYL)

Ribosome size of prokaryotes

70S, 50S large subunit and 30S small subunit

Size of Eukaryotic Ribosome

80S, 60S large subunit, 40S small subunit

What is the initiator tRNA in Prokaryotic translation?

N-formylmethionine

What is the imitatior tRNA in Eukaryotic translation?

AUG, methionine

Where does the ribosome initially bind to in prokaryotes?

Shine-Dalgarno sequence

Where does the ribosome bind to initially in Eukaryotes?

5’ cap

How many release factors do prokaryotes have in translation?

3, RF1, RF2 and RF3

What is the role of RF 1, 2 and 3 in Prokaryotic translation?

RF1 and 2 recognize stop codons and RF3 stimulates their activity. Promotes ribosome disassembly

How many release factors do Eukaryotes have for translation?

2, eRF1 and eRF3

What is the function of eRF1 and eRF3 in eukaryotic translation?

Recognize stop codons and GTP binding protein that helps eRF1 release the polypeptide

Where does translation occur in prokaryotes?

Cytoplasm

Where does translation occur in eukaryotes?

Cytosol

What does it mean when translation is coupled with transcription?

the ribosomes attach to mRNAa before transcription is complete

Is eukaryotic translation coupled with transcription

nah, transcription occurs in the nucleus, and translation occurs in the cytoplasm

How many combos of nitrogenous bases are there?

64

Germline mutations

Can be passed down to future generations, occurs in reproductive cells

Somatic mutations

Usually arises during life due environmental factors, can not be passed to future generations

A transition mutation

Change from a pyrimidine to another pyrimidine or a purine to another purine

Transversion mutation

change from a purine to pyrimidine or vice versa

Silent mutations

base substitutions that do not alter the amino acid of sequence of polypeptide

Missense mutation

base substitutions that alter the amino acid sequence- can be neutral or harmful

Nonsense mutation

Base substitution that can change a normal codon to a stop codon

Frameshift mutations

add or delete nucleotides not divisible by 3. Shifts the reading frame.

What did the Lederberg experiment determine?

The mutation for antibiotic resistance is spontaneous and arise’s randomly.

A reading frame

a way to divide nucleotide sequences into triplets

An open reading frame

A specific sequence within a reading frame that has a start codon and lacks a stop codon for a while- good candidate for coding a protein.

Spontaneous mutations

result from abnormalities in the biological process

Induced mutations

Chemical or physical agent known to alter DNA structure

Causes for spontaneous mutations include…

Depuration, deamination, tatuomeric shift

Deamination

Removal of an amino group from cytosine base- if not repaired C-G or A-T mutation occurs

Point mutations

effect a single nucleotide. Can be silent, missense or nonsense.

Frameshift mutations cause ____ protein changes

major

Some examples of mutagens

nitrous acid, nitrogen mustard gas, acridine dye, 5-Bromouracil

Some examples of physical mutagens

X-rays and UV light

Histone acetylation of chromatin causes…

Nucleosomes become loose and allow transcription factors to bind to DNA

DNA methylation of chromatin causes

Tightly packed nucleosomes. Transcription factors cannot bind.

What is dosage compensation?

genetic mechanism that ensure equal expression of X-linked genes between males and females.

In placental mammals, how is dosage compensation achieved?

One of the two x-chromosomes in somatic cells is randomly silenced to balance gene expression with males.

Cis-acting elements

DNA seqeunces that exert their effect over a particular gene (TATA box, enhancers, silencers) (Next to)

Trans-acting elements

Regulatory factors or proteins that bind to such DNA sequences. (across from)

Enhancers

Increase gene expression by promoting RNA pol. to bond and recruiting transcription factors

Enhancers bind to

Activators and coactivators

Silencers

Decrease or suppress gene expression. Block transcription or alter chromatin structure.

Silencers bind to

Repressors and corepressors

Eukaryotic transcription requires ___ ___ in addition to RNA polymerase

transcription factors

Transcription factors bind to _____ in order to ______

the promoter region to help recruit RNA polymerase for transcription initiation

3 Regulatory factors

Activators, Repressors, Mediators

Activators

Bind to DNA and facilitate or enhance transcription

Repressors

bind to DNA and silince or inhibit transcription

Mediators

can respond to hormones, stress or signals to modulate gene expression

General factors include

TFIID, TFIIB, TFIIE, TFIIF, TFIIH

TFIID

contains tata binding protein which recognizes tata box

TFIIB, E, F and H

Assist RNA polymerase II recruitment and transcription initiation

TFIIH

Has helicase activity which unwinds DNA and Kinase activity which phosphorylates RNA polymerase II to start transcription

Kinase

phosphorylates RNA polymerase II to start transcription

Common ways gene expression is regulated in transcription

Binding of small effector molecule, protein-protein interactions, covalent modifications

Allosteric interactions

binding to a non-active site on a protein, results in conformation and activity change.

Protein protein binding can cause ___

allosteric interactions

Covalent modifications

can activate or inhibit transcription factors via allosteric interactions EX. Phosphorylation

Effect of small effector molecule in transcription control

Regulates gene expression by modulating transcription factor activity. Activate or inhibits transcription factors, altering gene expression in response to environmental or cellular conditions.

A mutation on the promoter would likely…

weaken or eliminate RNA pol. binding. Causing lower transcription or complete loss of gene expression.

A mutation on the enhancer would likely ….

Prevent activators from binding. Transcription would be lowered and gene expression would be reduced

A mutation on the silencer would likely …

Prevent the repressor from binding, uncontrolled gene expression would increase.

siRNAs

Perfectly complementary to mRNA, degrades mRNA, exogenous

MicroRNA, miRNA

encoded in DNA (endogenous), primarily found on 3’ UTR, stored in processing body in cytoplasm.

Why is RNA processing considered a form of post transcriptional regulation?

If RNA is not spliced it can’t exit the nucleus for translation. If it cannot be translated it cannot be expressed.

What is the implication of phosphorylation on protein activity?

Could change how the protein works (Chromosome accessibility transcription factor binding, stability etc.)

Why in a multicellular organism, different cell types produce different gene products even though they contain the same genetic material?

because of a process called gene regulation, where each cell type selectively "turns on" or "turns off" specific genes based on signals from its environment, allowing it to express only the genes necessary for its specialized function, leading to distinct protein profiles for each cell type