Protein synthesis Flashcards
cell organelles involved in protein synthesis
- Nucleus
- Ribosome
- Endoplasmic reticulum
- Golgi body
what is a codon
group of three nucleotides (every three codes for a specific amino acid)
gene
group of codons (300-500) - codes for a specific protein
start codon
methionine
how many codons are there
64
how many codons code for amino acids
61
how many stop codons are there
3
what is the central dogma
the prosses of protein synthesis
- turning DNA to RNA and finally into a polypeptide
transcription (elongation)
- builds an mRNA strand that is complementary to the transcribed DNA strand with the substitution of uracil in place of thymine
transcription (initiation)
- RNA polymerase binds to the promoter segment of DNA
promoter region
- high in adenine and thymine
- a recognition site for RNA polymerase (TATA box)
template strand
strand of DNA the RNA polymerase is transcribing
coding strand
strand of DNA that is left alone during transcription
Transcription (termination)
- RNA polymerase releases once it hits the terminator sequence
after transcription
the hydrogen bonds reform once again connecting the DNA strands
post transcription modification
caping and tailing
caping
5’ cap is added to the start of mRNA
tailing
a string of 200 adenine ribonucleotides is added to the end 3’ with assistance from poly-A- polymerase giving it the name Poly- A- tail
Introns and Extrons
- introns are “useless” DNA and exons are important for protein synthesis/ folding
- introns are removed from mRNA after transcription, but before it leaves the nucleus
- if the introns are left in they will alter the folding of the protein rendering it usless
how are introns removed
- spliceosomes (remove introns and connect exons)
what happens to introns once they are removed
their nucleotides are broken down and recycled
ribosome structure
2 units, built independently and then joined together
- large subunit (60S)
- small subunit (40S)
binding sites A (acceptor cite) and P (peptide cite)
- each site can hold one codon at a time
purpose of the ribosome
translate mRNA and build the polypeptide chain
tRNA
- transfer RNA
- single-stranded nucleic acid (5’- 3’)
- cross-shaped
- delivers the indicated amino acids
- binds to ONE specific amino acid
anticodon
located on one of tRNA’s arms
- complementary to mRNA codons being read by the ribososme
aminoacyl-tRNA-synthetases
attaches the appropriate amino acid to tRNA
Translation (initiation)
ribosome recognizes and binds to the mRNA 5’cap
translation (elongation)
mRNA moves through the ribosome 5’-3’
- the starter codon conects at the p site and the following codon connects to the the a cite
what is the start codon
AUG
what bond connects the amino acids
peptide bond
termination step one
ribosome reaches the stop codon and the release factor will let go of the polypeptide chain
termination step 2
polypeptide enters the Golgi apparatus to be folded and stored or sent out right away in a vesicle
