chapter 17: from gene to protein

transcription

mRNA synthesis led by DNA

translations

polypeptide synthesis led by mRNA

mRNA

used to copy DNA code

template strand

DNA sequence that duplicated itself during mRNA synthesis

coding strand

DNA strand with a base sequence similar to that of RNA transcript

transcription factor

proteins that assist with binding between RNA polymerase and transcription initiation

5’- cap

cap on the 5’ end of an mRNA strand after transcription

3’- end poly-A tail

sequence of A nucleotides on the 3’ end of the mRNA strand after transcription

polyribosome

structure of a singular mRNA strand being fed through multiple ribosome at once. this allows for multiple copies of the same polypeptide to be made at once

mutagen

something that can cause mutations in DNA/RNA strand

metabolic pathway and relation to genes/proteins

• a metabolic pathway is the step-wise synthesis or break-down of molecules

• this relates to genes and proteins because genes are copied and step-wise created into proteins.

Beadle and Tatum experiment

• exposed different bread mold to x-rays to destroy different genes in the bread mold used to synthesize a protein

• resulted in the bread molds each producing different variants of a protein, each being dysfunctional

• idea of “one gene-one enzyme” emerged

“one gene-one enzyme” today

now become “one gene-one polypeptide”

genetic dogma

dna > rna > protein

RNA vs DNA

• RNA has U instead of T

• RNA can code for proteins

genetic code and why it’s called triplet

genetic code is a span of DNA which consists of 3 nucleotides coding for 1 amino acid.

codon

set of 3 nucleotides which code for amino acids

prokaryotic vs. eukaryotic transcription

• in prokaryotes, once the mRNA is made, translation immediately begins without any further modification

• prokaryotes have a terminator. eukaroytes have polyadenylation signal

• prokaryotes have no nuclear envelope so transcription and translation occur in same place

promoter and terminator in transcription

tells polymerase when to begin coding and when to stop coding

“transcription initiator complex”

• consists of RNA polymerase 2 and transcription factors bound to promoter

• only in eukaryotes

RNA processing and types of modifications

• occurs at ends of primary transcription

• 5’ end gets cap and 3’ gets poly-A tail

• some interior parts are cut out or spliced together

intron vs. exon

intron: non-expressed region of a code

exon: coding-region which can be eventually expressed

RNA splicing

introns being removed and exons being spliced together

ribozyme

catalytic RNA molecule used in RNA splicing

spliceosome and role in RNA processing

• consists of snRNPs, snRNA, and proteins

• removes introns and splices exons together

alternative RNA splicing

some genes code for different versions of polypeptides depending on what is classified as intron or exon during splicing

exon shuffling

• exons brought over from different sequence or exons are duplicated

• results in new genes

anticodon and location in structure

• sequence of amino acids on one end of a tRNA molecule that base pairs with a mRNA codon

• located at bottom of tRNA

charged tRNA and energy molecule used

• aminoacyl-RNA. it corrects tRNA and amino acid match

• ATP

what end of tRNA molecule contains amino acid attachment site

3’ end

ribosome

• consists of large and small subunit, composed of rRNA.

• facilitates copying of tRNA and mRNA

components of translation initiation complex and energy used

• proteins, small and large subunit

• GTP used

functions of E, A, and P sites

• E: exit site for tRNA

• A: holds tRNA that has the next amino acid for protein

• P: holds the growing chain and tRNA

which end of polypeptide first emerges from ribosome

amino end

post-translational modification of protein

• folding

• attaching sugars, lipids, phosphate groups, etc.

how are polypeptides tagged for certain locations within the cell

has a protein “address label”

signal peptide and signal recognition particle

• signal peptide: bonds to peptides destined for ER or excretion

• particle: binds to signal peptide and brings it to ER

point mutation

chemical changes in one base pair

missense mutation

a change in the code that still results in a protein, but not the right one

nonsense mutation

change in code that doesn’t make a functional protein

silent mutation

change in code which doesn’t affect the protein

mutation most likely to cause major protein changes

base-pair

frameshift mutation

change in code where the entire code is read in a different way, causing the entire protein to be changed rather than just one amino acid