Genetics Final Exam Study Guide

Ch 10.5-13

What are the 3 primary regions of mRNA sequences in bacterial cells?

1) 5’ untranslated region

2) Proton-coding region

3) 3’ untranslated region

Shine-Dalgarno sequence

Ribosome-binding site on mRNA in prokaryotes for TRANSLATION

Complementary to part of 16s rRNA of small rRNA

5’ cap

5’ end of eukaryotic mRNA

Has extra G linked 5’ to 5’ in mRNA

Spliceosome

Form at splice sites on pre-mRNA

Include snURPs

Removes pre-mRNA & joints exons (splicing)

Splicing

Removing pre-mRNA introns & joining exons

Alternative splicing

Allows pre-mRNA from a single gene to be spliced in multiple ways

How does alternative splicing allow for the production of multiple genes?

Parts of nucleotides can be treated as an intron or an exon

Single gene → multiple mRNAs → multiple polypeptides

Different types of processing that can happen in mRNAs

1) Adding 5’-7-methylguanosine cap to 5’ end of mRNA

2) Cleaving at site downstream from of AAUAAA consensus sequence at 3’ end of pre-mRNA

3) Adding poly(A) tail to 3’ end of mRNA

4) Removing introns (splicing)

Describe tRNA processing

1) Excising 5’ leader

2) Excising 3’ tail

3) Removing intron

4) Adding bases

Small interfering RNAs/siRNAs

Result from Dicers cleaving mRNAs, RNA transposons, and RNA viruses

Silence gene expression via RNA interference

microRNAs

Result from cleaving longer RNA molecules

Silence gene expression via RNA interference

List the components in a eukaryotic gene

• 5’ untranslated region

• Promoter

• AAUAAA consensus sequence

• Transcription start site

• Introns

• Exons

• Poly(A) Tail

• 5’ cap

5’ untranslated region in eukaryotes

Lies upstream of transcription start site

Ribosome binds at 5’ cap on mRNA

Scans AUG (methionine)

Promoter

DNA sequence recognized

Bound to to start transcription

AAUUAAA consensus sequence

Lies near 3’ end of pre-mRNA

Determines where 3’ cleavage and adding PolyA tail happens

Transcription start site

Located 25-30 nucleotides downstream of TATA box on promoter

TATA box

At 10 bp

Enzyme in prokaryotic initiation

RNA Polymerase

Has a sigma factor

Synthesizes mRNA (often polycistronic)

How many RNA Pol do prokaryotes have?

1

How many subunits do prokaryotes have?

6

How many subunits do prokaryotes need for transcription?

5

Introns

Noncoding intervening DNA sequences

Exons

Expressed DNA sequences

snURPS

Small nuclear ribo-proteins

Lupus erythematorus

Autoimmune disease where antibodies recognize snURPS as foreign & destroys them

Poly(A) Tail

Added to 3’ end of pre-mRNA

Affects mRNA stability

Initiation codon for translation

Establishes appropriate reading frame

Usually AUG

Termination codon/Nonsense codons for translation

Signals the end of translation

3 possible: UAA, UAG, UGA

What are the 3 termination codons?

1) UAA
2) UAG

3) UGA

Sense codon

Group of 3 nucleotides that code for an amino acid

61 sense codons

What are the 3 initiation factors in prokaryotes?

1) IF-1

2) IF-2

3) IF-3

Initiation factor IF-1

Dissociates of large & small ribosomal subunits

In prokaryotes & eukaryotes

Initiation factor IF-3

Binds to smRNA to prevent it from associating w/ the large ribosome

In prokaryotes

Initiation factor IF-2

Binds GTP and delivers fMet-tRA to initiator codon on mRNA

In prokaryotes

What does AUG code for in eukaryotes?

Methionine

What does the AUG codon code for in prokaryotes?

N-formylmethionine

Where does transcription happen?

Nucleus

Where does translation happen?

Cytoplasm

T/F: Prokaryotic mRNA has a 5’ cap and poly(A) tail

False

Polycistronic messages

Many coding units that encode proteins

In prokaryotes

List the enzymes in elongation of transcription (both prokaryotes and eukaryotes)

• Topoisomerase I

• Topoisomerase II

Topoisomerase I

Makes 1 nick

In prokaryotes or eukaryotes

Toipoisomerase II

Makes 2 nicks

In prokaryotes and eukaryotes

What are the 2 types of prokaryotic termination of transcription?

1) Rho-independent

2) Rho-dependent

Rho-independent termination

Intrinsic DNA transcribed into nascant (growing) 3’ end of RNA

Encode inverted sequence into RNA strand

Rho-dependent termination

Requires intrinsic DNA

Recognized by Rho protein

Helicase activity

Translocates 5’ → 3’

Pol falls off

Anti-terminators

Change site of transcription

Bind to RNA Pol complex

Change function, structure, and location of proteins

What type of chromatin is used in eukaryotic transcription?

Euchromatin

Core promoter

Minimum sequence necessary for eukaryotic transcription

How do you identify core promoters?

Reporter genes

1) Make DNA construct w/ promoter upstream of gene

2) Reporter tests if promoter actually promotes expression

3) Cut promotor until it’s no longer expressed

Consensus sequence in eukaryotes

TATA or Goldberg-Hg

5’ → 3’

Work regardless of orientation (5’ → 3’ or 3’ to 5’)

Where is the consensus sequence in prokaryotes?

-35 bp

Where is the consensus sequence in eukaryotes?

-30 bp

Alternate g mutation

Some of transcribed exon is lost

Retention mutation

Keeps an intron on accident

Likely a premature stop

Alternation mutation

Skips an exon

Colinearity

Read 5’ → 3’, N → C

Wobble Hypothesis

3 base codon BUT 3rd base can vary

Initiation of translation in prokaryotes

1) 30 s ribosome subunit binds to ribosome

2) Charged tRNA w/ N-formymethiamine

3) Shine-Delgarno sequence binds upstream of AUG

4) Needs IF-3

5) Forms 3 sites

What are the sites formed after initiation of translation?

1) P-site

2) A-site

3) E-Site

P-site

tRNA w/ peptide chain

Prokaryotic & eukaryotic translation

A-site

Acceptor site for next tRNA

In prokaryotic translation

E-site

Exit site where charged tRNA leaves

In prokaryotic translation

Translation elongation in prokaryotes

1) Charged tRNA enters A-site w/ elongation factor

2) Peptidyltransferase forms peptide bond b/w carboxyl group on P-site w/ NH2 group of the amino acids on the A-site

3) Translocation

Elongation factor (EF-Tu)

Joins w/ GTP & charged tRNA to enter A-site on ribosome

Translocation

Ribosome moves down RNA in a 5’ → 3’ direction

Summary of elongation of a ribosome

Cytoplasm → A site → P site → E site → cytoplasm

Eukaryotic termination

No tRNAs for stop codon

GTP links b/w peptide on tRNA & P-site

Polysomes

Multiple ribosomes translations from single mRNA

Streptomyocin

Antibody that alters pairing of tRNA to its codon

Alters decoding mRNA

Aminoglycosides

Binds 30s subunits

Blocks initiation

Blocks tRNA from binding to future P-site

Chloramphenical

Antibody that inhibits peptidyl-transferase

No peptide bond formation b/w p-site and a-site

Erythromyocin

Antibody that binds 50s particle

Inhibits translocation

Puromyocin

Antibodies that terminates chains

Can enter A-sites b/c it looks like a tRNA

Terocyclines

Antibody that blocks tRNA entry into the A-site

Frame shift mutation

Gain/loss of 1 or more bases that aren’t a multiple of 3

OR splice change that disrupts the reading frame

Introduce stop codon

Silent mutation

3rd base varies

No change in amino acids

Missense mutation

Change in amino acids

Nonsense mutations

Causes premature stopping

Deletions

Loss of bases

Single or large chunk of chromosomes

Not all cause change in phenotypes

Insertion

Inserting a single base

In/del

Insertion and deletion on the same chromosome

CRISPRs

Rearrangements

Mutations that include translocations

Revertants

Novel mutation that reverts mutant allele/phenotype to the wildtype

Trans revertants

Changes in tRNA anticodons

Point mutations

Single base mutations

Types of spontaneous mutations

1) Deamination

2) Depurination

Transitions

Mutations that transform purines to purines or pyrimidines to pyrimidines

Transversions

Mutations that change purines to pyrimidines or vice versa

What does it mean when something is sensitive after complementation?

It fails to compliment, so genes are from the same locus

What does it mean when something is insensitive after complementation?

It compliments, so genes aren’t on the same locus

Xeroderma Pigmentosa

Disease that gives someone a higher risk of skin cancer

Found via somatic cell hybridization

Unscheduled DNA synthesis deficiency

Somatic cell hybridization

Test where you fuse 2 cells w/ UV light to see if they compliment each other

Used to find Xeroderma Pigmentosa

Fragile X Syndrome

Trinucleotide repeat expansion

Testicular feminization

Male XY

Disease with androgen sensitivity

Leads to developing as physically female

TUNEL

Label DNA of apoptotic cells

Amniocentesis

Test for chromosomal aberrations of a fetus

Aminoacyl tRNA synthetase

Class of enzymes that catalyze reaction b/w tRNA and an amino acid

In prokaryotes, UV damage of DNA is reversed by

Enzyme mediated photoactivation repair

Which of the following enzymatic activities is NOT present during base excision repair ?

Primase adds RNA primer to template