3.4.2 - DNA and protein synthesis

Question 1

what is the genome?

Answer 1

the complete set of genes in a cell

Question 2

what is the proteome?

Answer 2

the full range of proteins that a cell is able to produce

Question 3

what is the role of mRNA?

Answer 3

messenger RNA has a base sequence complementary to DNA and carries the genetic sequence needed to make proteins to the ribosomes

Question 4

what is the structure of molecules of mRNA?

Answer 4

it is a long, single strand directly transcribed from DNA, with bases arranged in groups of 3 called codons

Question 5

what is the role of tRNA?

Answer 5

transfer RNA carries and transfers amino acids to the ribosomes during translation

Question 6

what is the structure of molecules of tRNA?

Answer 6

it is a single strand folded into a clover leaf shape - creates an attachment site for amino acids at one end and anti-codons at the other end

Question 7

what is transcription?

Answer 7

the production of mRNA from DNA

Question 8

what happens during transcription?

Answer 8

1. the DNA unzips at a specific region (gene), breaking the hydrogen bonds between complementary bases
2. free RNA nucleotides base pair with the template strand
3. RNA polymerase moves along the template strand joining mRNA nucleotides forming a strand of pre-mRNA/mRNA
4. RNA polymerase continues along the template strand until it reaches a stop codon
5. the hydrogen bonds between the two DNA strands reform as the RNA polymerase moves along and the mRNA detaches

Question 9

what happens with transcription in prokaryotes?

Answer 9

it results directly in the production of mRNA from DNA

Question 10

what happens with transcription in eukaryotes?

Answer 10

transcription results in the production of pre-mRNA, which is spliced to form mRNA

Question 11

what happens during splicing?

Answer 11

introns are spliced from pre-mRNA, and the exons rejoin together to form mRNA which leaves

Question 12

what can occur due to incorrect splicing?

Answer 12

it can lead to certain disorders due to the production of incorrect polypeptides eg. Alzheimer’s, beta-thalassemia

Question 13

what is translation?

Answer 13

the production of polypeptides from the sequence of codons carried by mRNA

Question 14

what happens during translation?

Answer 14

1. mRNA passes out of the nucleus through the nuclear pores
2. a ribosome attaches to the mRNA at the start codon
3. a complementary tRNA molecule carrying a specific amino acid moves to the ribosome and its anticodon pairs up with the first codon (two codons fit inside the ribosome at a time)
4. the next tRNA molecule with its amino acid joins to the second codon
5. a condensation reaction takes place between the amino acids forming a peptide bond (reaction requires an enzyme and ATP)
6. the ribosome moves along the mRNA, releasing the first tRNA molecule and allowing a third to bind
7. this process repeats until the stop codon is reached
8. the polypeptide is released

Question 15

what is the main role of ATP in translation?

Answer 15

ATP binds tRNA to the amino acid it is bringing into the ribosome