Chapter 3: Section B: Protein Synthesis, etc Flashcards Preview

ONLINE PHYSIOLOGY > Chapter 3: Section B: Protein Synthesis, etc > Flashcards

Flashcards in Chapter 3: Section B: Protein Synthesis, etc Deck (18):
1

Gene

- sequence of DNA nucleotides that codes for one polypeptide (unit of heredity)
- amino acid sequence

2

Genome

- 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

Transcription

- process by which the genetic info in the DNA is copied into mRNA
- catalyzed by RNA polymerase
- occurs in nucleus

4

Translation

- 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

stages of transcription

- 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

mRNA processing

- 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

The genetic code

- 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

codon

3 nucleotide sequence that codes for one a.a.

9

Start codon

AUG (methionine)

10

Stop codons

- UAA
- UAG
- UGA

11

Translation steps

- initiation: translation begins (requires AUG codon)
- elongation: polypeptide chain grows
- termination: translation stops (requires stop codon)

12

Initiation of translation

- 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

Elongation of translation

- 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

Termination of translation

- occurrs when stop codon enters 'A site'
- polypeptide chain is released from the ribosome
- ribosome dissociates
- an mRNA is polyribosomal

15

Post-translational processing

- proteins processed after translation complete
- cleaving = sections of proteins are cut off of one another = efficient way of creating many proteins

16

Mutations

- an alteration in the nucleotide sequence of DNA

17

possible effects of mutations

- no change in cell function
- modified cell function compatible with life
- cell death

18

Protein secretion

- proteins that will be secreted from cell or that will become integral membrane proteins have a signal sequence
--> first 15-30 amino acids added during translation
- proteins that will remain in the cell do not have a signal sequence