3.4.2 (protein synthesis) Flashcards
Genome
Complete set of genes in the cell
Proteome
Complete range of proteins the cell is able to make
Describe the structure of mRNA
Long single helix strand
Possesses information in the form of codons
Only contains exons (introns have been spliced)
Chemically unstable
Describe the difference between pre mRNA and mRNA
Pre mRNA contains introns and exons whereas mRNA contains only exons
What are codons?
A series of 3 bases on mRNA
Describe the structure of tRNA
Small
Single stranded- folded into clover shape, held by hydrogen bonds/ complementary base pairing
Around 60 different tRNAs, each with a specific anticodon that attaches to a specific amino acid recognised by different enzymes
3 bases form the anticodon
Double or single stranded (DNA, mRNA, tRNA)
DNA- double polynucleotide chain
mRNA- single polynucleotide chain
tRNA- single polynucleotide chain
Size (DNA, mRNA, tRNA)
DNA- largest
mRNA- smaller
tRNA- smallest
Shape (DNA, mRNA, tRNA)
DNA- double helix
mRNA- single helix
tRNA- clover shaped
Pentose sugar (DNA, mRNA, tRNA)
DNA- deoxyribose
mRNA- ribose
tRNA- ribose
Bases (DNA, mRNA, tRNA)
DNA- T A G C
mRNA- U A G C
tRNA- U A G C
Where is it found (DNA, mRNA, tRNA)
DNA- mostly nucleus, some mitochondria+chloroplast
mRNA and tRNA- made in nucleus, moves into cytoplasm
How does quantity vary in different cells of same species (DNA, mRNA, tRNA)
DNA- same in all diploid cells, gametes have half amount
mRNA and tRNA- quantity varies from cell to cell, depending on metabolic rate and protein synthesis demands
Chemical stability and why (DNA, mRNA, tRNA)
DNA- chemically very stable, made to persist through generations
mRNA- least stable, broken down quickly to ensure polypeptide synthesis doesn’t continue indefinitely
tRNA- more stable than mRNA but less than DNA, can be used multiple times
Name the 2 processes in protein synthesis
Transcription
Translation
Describe transcription
DNA helicase enzyme unzips a short section of DNA exposing the bases- one strand becomes template strand
Free RNA nucleotides in nucleoplasm are attracted to complemementary exposed bases
RNA polymerase joins nucleotides by phosphodiester bonds (DNA strands rejoin at same time) until it reaches a stop codon when it detaches
Pre mRNA undergoes splicing (in eukaryotes) to remove introns and leaves nucleus through a nuclear pore
Why does pre mRNA undergo splicing?
To remove introns
Why do prokaryotes not undergo splicing?
Splicing is the removal of introns
Prokaryotes do not contain introns
Summarise translation
Code on mRNA used to assemble a polypeptide
Takes place on ribosomes
Describe translation
mRNA leaves nucleus and is attracted to ribosomes
Ribosome attaches to first two codons
tRNA molecule with complementary anticodon carrying specific amino acid pairs with code on mRNA
Repeats for next codon
The two amino acids are joined by a peptide bond using an enzyme to catalyse and ATP to supply energy
Ribosome moves along by one codon
First tRNA is released
Continues until it reaches stop codon
