DNA and protein synthesis Flashcards
What is a genome?
The complete set of genes in a cell
Describe the structure of mRNA and pre mRNA
Pre mRNA > RNA before splicing > contains introns and exons
mRNA > single stranded molecule > sugar phosphate backbone > nucleotides attached by phosphodiester bonds > carries genetic information for coding
Describe the process of protein synthesis (4)
1) DNA provides the instructions in the form of a long sequence of bases
2) Complementary section of part of sequence is made by pre mRNA > transcription
3) Pre mRNA is spliced to form mRNA
4) mRNA used as template > complementary tRNA molecules attach > amino acids that tRNA carry are linked > to form a polypeptide > translation
What is the role of transcription?
Making pre mRNA using part of the DNA asa a template
Describe the process of transcription
1) DNA helicase > Enzyme acts on specific region of the DNA > causing 2 strands to separate > expose nucleotide bases in region
2) Nucleotide bases on template strand pair with complementary nucleotides from pool present in the nucleus
3) Enzyme DNA polymerase moves along strand > joins nucleotides together > to form a pre mRNA molecule
4) DNA strand rejoins behind DNA polymerase
5) When RNA polymerase reaches particular sequence of bases on DNA > recognises as STOP triplet code > enzyme detaches > PRODUCTION OF pre mRNA COMPLETE
In prokaryotic cells what does transcription result in?
Directly in the production of mRNA from DNA > as they don’t have introns > splicing is not necessary
Describe the structure of tRNA?
- Clover like structure
- Single strand of RNA > with several loop structures
- Loops contain specific sequences of nucleotides that are important for tRNA function
Why do introns need to be removed by splicing? (2)
1) Would prevent the synthesis of polypeptides
2) mRNA molecules are too large to diffuse out of nucleus
Describe the process of splicing (2)
1) The base sequences corresponding to the introns are removed
2) Functional exons are joined together
What happens once mRNA has left the nucleus?
mRNA is attracted to the ribosomes and becomes attached > ready for translation
Describe the process of translation (7)
1) A ribosome becomes attached to starting codon at one end of mRNA molecule
2) tRNA molecule with complementary anticodon sequence moves to ribosome > pairs up with codon on mRNA
3) tRNA molecule with complementary anticodon > pairs up with next codon
4) Ribosome moves along mRNA > bringing together two tRNA molecules at any one time
5) Two amino acids on tRNA are joined by a peptide bond > using enzyme and ATP
6) As the next amino acid is being coded for > first tRNA molecule is released > free to collect another amino acid from a/a pool
7) Process continues until ribosome reaches stop codon > ribosome
, tRNA, mRNA separate
POLYPEPTIDE CHAIN IS FORMED
What is the relationship between DNA, mRNA and tRNA?
DNA sequence of triplets determine sequence of codons on mRNA > determines order in which tRNA molecules line up
