Protein Synthesis

Question 1

What is a codon?

Answer 1

The triplet base sequence that determines what amino acid is produced.

Question 2

What does messenger RNA do?

Answer 2

mRNA carries the instructions needed for protein synthesis.

Question 3

What is transcription?

Answer 3

A particular segment of DNA (template strand) is copied in the first step to protein synthesis. New strand is mRNA.

Question 4

Method for transcription.

Answer 4

1. Helicase unzips the DNA strand.
2. A DNA template is used to make mRNA.
3. The DNA sequence to be copied begins with a promoter.
4. RNA polymerase bonds to the promoter region, creates the complementary mRNA strand, a stop signal is reached and mRNA is released.
5. The mRNA moves into the cytoplasm via pores in the nuclear membrane.

Question 5

What is mRNA made up of?

Answer 5

Introns- base sequences that aren’t translated into amino acids.
Exons- base sequence which codes for amino acids.

Question 6

PremRNA

Answer 6

Has a methylated cap added at the 5’ end and 100-200 adenines at the 3’ end called the poly-Atail.

Question 7

What is translation?

Answer 7

The process when a ribosome synthesises polypeptides (protein) from mRNA codons.

Question 8

Ribosome

Answer 8

Ribosomes are made up of 2 subunits, and are found in the cytoplasm or on the rough er.

Question 9

tRNA

Answer 9

Transfer (or carry) amino acids to ribosomes.
Free-floating in the cytoplasm.

Question 10

What is an anti-codon?

Answer 10

The three nucleotide bases at the bottom.

Question 11

Stages of translation

Answer 11

1. Ribosome recognises mRNA coming from the nucleus.
2. Ribosome binds to methylated cap on mRNA and moves along mRNA scanning for a start codon ‘AUG’.
3. Ribosome has a site for tRNA’s anti-codon to bond with mRNA’s codon and release the amino acid.
4. Ribosome moves onto the next codon on the mRNA and repeats steps three and four, each time an amino acid is added to the growing polypeptide chain.
5. This continues until a stop-codon is reached.
6. Peptide bonds form between the amino acids to create the polypeptide chain, which is released.
7. mRNA is broken down into nucleotides to be reused in transcription.

Question 12

Genetic Code

Answer 12

Shows the relationship between the mRNA codons and amino acids.
Several (triplet) codes can code for one amino acid.