Chapter 7 RNA and the Genetic Code

Central Dogma

DNA is transcribed to RNA, which is translated into protein

Gene

unit of DNA encoding specific protein or RNA through transcription and translation

What direction is mRNA written in?

5 to 3

mRNA

carry out information specifying AA sequence of protein to ribosome

Codons

3 nucleotide sequences

Degenerate Code

allows multiple codons to encode for same AA

Initiation Codon

AUG

Termination Codons

UAA, UGA, UAG

Redundancy and Wobble

allows mutations to occur without effects in proteins

Point Mutations Types

silent, nonsense, missense

Silent Mutation

no effect on protein synthesis

Nonsense Mutation

produce premature stop codon

Missense Mutation

produce codon that codes for different AA

Transfer RNA

convert language of nucleic acids to language of AA and peptides

Anticodon

recognizes and pairs with appropriate codon on mRNA in ribosome

Ribosomal RNA

synthesized in nucleolus, assembles proteins in cytoplasm

Frameshift Mutation

result from nucleic acid addition or deletion

Transcription

creation of mRNA from DNA template

Helicase

unwinds DNA double helix

Promoter Region

DNA portion upstream, contains TATA box, RNA polymerase II binds to start transcription

TATA Box

high concentration of A and T

Transcription Factors

help RNA polymerase locate and bind to promoter region of DNA for transcription start

Post Transcriptional Processing

intron/extron splicing, 5 cap, 3 poly-A Tail

Intron

noncoding E

Extron

coding

Splicing

intron removed and exon ligated

Spliceosome

snRNP splices 5 to 3 end of intron

5’ Cap Function

protects mRNA from degradation in cytoplasm

3’ poly-A Tail Function

exports mature mRNA from nucleus

Alternative Splicing

combine different exons to make different gene products

tRNA

translates codon into correct AA

Ribosomes

factories where translation occurs

Nuclear Pores

where mRNA exits nucleus

Translation

converting mRNA into functional protein

DNA to DNA

replication, new DNA synthesized in 5, 3

DNA to RNA

transcription, new RNA synthesized in 5, 3 template read 3, 5

RNA to Protein

translation, mRNA read in 5, 3

Stages of Translation

initiation, elongation, termination

Initiation

ribosome attaches to binding site and scans for start codon

Where do prokaryote ribosomes attach in initiation?

Shine-Dalgrano Sequence

Where do eukaryotes attach in initation?

5 cap

Elongation A Site

addition of aminoacyl-tRNA

Elongation P Site

transfer polypeptide chain from tRNA from P to A

Elongation E Site

uncharged tRNA pauses before exiting to unbind from mRNA and be recharged

Termination

codon in A site is stop codon

Termination Release Factor

water placed on polypeptide chain, releasing protein

Posttranslational Modifications

chaperones, quaternary structure, cleavage, covalent addition

Chaperones

fold proteins

Covalent Addition of Biomolecules

phosphorylation, carboxylation, glycosylation, prenylation

Glycosylation

addition of sugars

Prenylation

addition of lipid groups

Jacob-Monod Model

explains how operons work

Operons

cluster of genes transcribed as single mRNA

Structural Gene

codes for protein of interest

Operator Site

upstream, non-transcribable region of DNA capable of binding repressor protein

Promoter Site

upstream, provides place for RNA polymerase to bind

Regulator Gene

codes for repressor protein

Inducible System

bonded to repressor under normal conditions

How can an inducible systems turned on?

inducer pulls repressor from operator site

Repressible Systems

transcribed under normal conditions

How are repressible systems turned off?

corepressor couples with repressor and binds to operator site

Transcription Factors

search for promoter and enhancer regions in DNA

Promoters

within 25 base pairs of transcription start site

Enhancers

more than 25 base pairs from transcription start site

Enhancer Examples

cAMP, cortisol, estrogen

Heterochromatin

tightly coiled inactive DNA that appears dark under microscope

Euchromatin

looser active DNA that appears light under microscope

How does histone acetylation affect transcriptional enzymes accessibility to DNA?

increases

How does DNA methylation affect transcriptional enzymes accessibility to DNA?

decreases