Chapter 3: Section B: Protein Synthesis, etc Flashcards
1
Q
Gene
A
- sequence of DNA nucleotides that codes for one polypeptide (unit of heredity)
- amino acid sequence
2
Q
Genome
A
- all genetic info in a single cell ~30,000 genes
- 46 chromosomes per diploid cell
- each chromosome composed of 1 DNA molecule organized around histone proteins
3
Q
Transcription
A
- process by which the genetic info in the DNA is copied into mRNA
- catalyzed by RNA polymerase
- occurs in nucleus
4
Q
Translation
A
- process by which ribosomes use the info in mRNA to assemble the protein
- occurs in cytoplasm and involves ribosomes
- DNA –> transcription –> mRNA –> translation –> protein
- requires mRNA, tRNA, ribosomes and enzymes
- tRNA determines which a,a, is put in new protein
5
Q
stages of transcription
A
- RNA polymerase binds to DNA at the promoter site (promoter indicates start of a gene or unit of genes)
- RNA polymerase unwinds a portion of the DNA helix
- RNA polymerase moves along DNA template strand and assembles RNA molecule by adding nucleotides complementary to the template
- RNA polymerase separates from the DNA, the new RNA molecule is released from the DNA and the DNA rewinds
6
Q
mRNA processing
A
- before mRNA moves from nucleus to cytoplasm
- 5’ cap added
- 3’ poly-a-tail added
- splicing = introns are removed and exons (coding regions) are ligated
7
Q
The genetic code
A
- sequence of nucleotides in the mRNA molecule is organized in codons
- triplet code
- it determines which amino acid will be placed in each position of the protein
8
Q
codon
A
3 nucleotide sequence that codes for one a.a.
9
Q
Start codon
A
AUG (methionine)
10
Q
Stop codons
A
- UAA
- UAG
- UGA
11
Q
Translation steps
A
- initiation: translation begins (requires AUG codon)
- elongation: polypeptide chain grows
- termination: translation stops (requires stop codon)
12
Q
Initiation of translation
A
- mRNA bind to small ribosomal subunit w/AUG codon oriented in what will be the ‘P site’
- the anticodon of a AUG-tRNA complementary base-pairs with the AUG codon
- large ribosomal subunit joins the complex, forming a complete ribosome with A, P and E sites
13
Q
Elongation of translation
A
- a tRNA with an anticodon complementary to the codon in the ‘A site’ enters the ‘A site’
- the amino acid on tRNA in ‘P site’ is transferred to ‘A site’ where a peptide bond forms between it and the amino acid on the tRNA is the A site
- translocation occurrs (ribosome moves one codon to right)
- elongation continues until stop codon reached
14
Q
Termination of translation
A
- occurrs when stop codon enters ‘A site’
- polypeptide chain is released from the ribosome
- ribosome dissociates
- an mRNA is polyribosomal
15
Q
Post-translational processing
A
- proteins processed after translation complete
- cleaving = sections of proteins are cut off of one another = efficient way of creating many proteins
