protein synthesis

Question 1

Where do transcription and translation occur? (2)

Answer 1

Transcription = occurs in the nucleus

Translation = occurs at ribosomes in the cytoplasm

Question 2

What happens during transcription? (1)

Answer 2

The DNA strand is transcribed into pre-mRNA

Question 3

What happens to pre-mRNA after transcription before translation? (2)

Answer 3

Pre-mRNA is spliced

To remove their introns (non-coding DNA)

Question 4

What happens during translation? (2)

Answer 4

Amino acids are assembled

To form a polypeptide chain

Question 5

What is mRNA? (3)

Answer 5

Made in the nucleus

3 adjacent bases are called a codon

Carries the genetic code from the DNA to the cytoplasm

Question 6

What is tRNA? (3)

Answer 6

Found in the cytoplasm

Has an amino acid binding site at one end and an anti-codon at the other

Carries amino acids to the ribosomes.

Question 7

What is rRNA? (2)

Answer 7

Forms the two subunits of the ribosome along with proteins

Helps catalyse the formation of peptide bonds between amino acids during protein synthesis

Question 8

What happens during transcription? (5)

Answer 8

1. Hydrogen bonds between complementary bases break, and the DNA helix uncoils.
2. RNA polymerase uses one strand of DNA (the antisense strand) as a template to make the mRNA molecule.
3. Free RNA nucleotides line up by complementary base pairing, and adjacent nucleotides are joined by phosphodiester bonds, catalysed by RNA polymerase.
4. When RNA polymerase reaches a stop codon, it detaches from the DNA.
5. The mRNA moves out of the nucleus into the cytoplasm through a nuclear pore.

Question 9

What happens first in translation? (1)

Answer 9

mRNA attaches to a ribosome

Question 10

What is the role of tRNA in translation? (2)

Answer 10

tRNA molecules carry amino acids to the ribosome

tRNA attaches to mRNA by complementary base pairing between the codons of the mRNA and the anti-codons of tRNA

Question 11

How are amino acids joined during translation? (3)

Answer 11

1. Two tRNA molecules attach to the mRNA one at a time
2. The amino acids are joined by a peptide bond
3. Catalysed by rRNA

Question 12

What happens after the first tRNA detaches? (2)

Answer 12

1. A third tRNA molecule binds to the next codon on the mRNA
2. A peptide bond is formed between the second and third amino acids, and the second tRNA molecule detaches

Question 13

How does the process of translation continue? (1)

Answer 13

With the formation of a polypeptide chain as amino acids are added

Question 14

When does translation stop? (2)

Answer 14

When a stop codon is reached;

On the mRNA