3.4.2 - DNA and protein synthesis

Question 1

Define genome

Answer 1

complete set of genes in a cell

Question 2

Define proteome

Answer 2

full range of proteins that the genome is able to code for

Question 3

What is the function of mRNA?

Answer 3

complementary strand to the DNA which carries genetic code from DNA to the ribosomes (transcription)

Question 4

What is the function of tRNA?

Answer 4

carries amino acids to the ribosomes so a polypeptide chain can be formed (translation)

Question 5

Describe the structure of mRNA

Answer 5

• single polypeptide strand made during transcription - the base sequence is determined by the sequence on DNA

Question 6

Describe the structure of tRNA

Answer 6

• single stranded chain
• clover leaf shape
• small (around 80 nucleotides)
• Has an ANTICODON which is complementary to a specific codon on an mRNA molecule
• has an antibody binding site
• has hydrogen bonds due to folding

Question 7

How would you figure out the DNA sequence from an mRNA sequence?

Answer 7

mRNA is a complementary copy of the DNA template so they will be opposites (eg is mRNA is UCU then DNA will be AGA)

Question 8

How would you figure out the tRNA anticodons from the mRNA codons?

Answer 8

tRNA will be a complementary copy of the mRNA - opposites
- will be the same as the original DNA sequence bu with uracil instead of thymine

Question 9

What is DNA transcription?

Answer 9

DNA provides instructions via a long base sequence - a complementary strand is made in the form of pre-MRNA which is then spliced to form MRNA

Question 10

What is DNA translation?

Answer 10

mRNA acts as a template - complementary tRNA attaches and the amino acids they carry are joined to form a polypeptide chain

Question 11

Describe the main steps of transcription?

Answer 11

1. **Hydrogen bonds between DNA bases break and the strands separate to expose the nucleotide bases - one strand acts as a template
2. nucleotide bases pair with the complementary free nucleotides
3. RNA polymerase attaches to the** template strand and joins adjacent RNA nucelotides - phosphodiester bonds
   4. Pre-mRNA is formed **
4. DNA strands rejoin behind this
5. Stop triplet is reached and and** RNA polymerase detaches** and production of pre-mRNA is complete
6. Splicing - introns are removed and exons join to form mRNA
7. mRNA diffuses out of the nuceus via a nuclear pore and is attracted to ribosomes for translation

Question 12

Describe the main steps of translation?

Answer 12

1. mRNA molecule associates with ribosome in the cytoplasm
2. first two mRNA codons on the ribosome bind to the complementary anticodons on the tRNA - each one carries a **specific amino acid
   3. peptide bond forms **between adjacent amino acids - requires an enzyme and ATP hydrolysis
3. ribosome moved forward one codon - first tRNA is released from the ribosome (free to collect another amino acid) and a new tRNA enters - another** peptide bond forms **between second amino acid and new amino acid
4. ribosome continues moving along mRNA until it reaches a **stop codon **- Polypeptide chain is formed