Biology: Unit 2 module 1 - Cellular Control

Question 0

How does transcription occur?

Answer 0

1. The gene to be transcribed unwinds and unzips. To do this, the length of DNA that makes up the gene dips into the nucleolus and hydrogen bonds between complementary bases break.
2. RNA nucleotides bind with the exposed complementary bases.
3. The mRNA produced us complementary to the base sequence of the original strand of DNA and therefore is a copy.
4. The mRNA released from the DNA passes out of the nucleus through a pore in the nuclear envelope. And to a ribosome.

Question 1

What is a gene?

Answer 1

A length of DNA which codes for one or more polypeptides.

Question 2

What is translation?

Answer 2

The formation of polypeptides at a ribosome.

Question 3

Why is the sequence of amino acids in a protein critical?

Answer 3

It forms the primary structure of the protein, which determines the tertiary structure. The tertiary structure is the 3D shape that gives the protein its function.

Question 4

What is transfer RNA?

Answer 4

tRNA is made in made in the nucleus and then released into the cytoplasm. They are lengths of RNA which fold into hairpin shapes. They have three bases exposed at one end where a complimentary amino acid binds. The other end contains an anticodon, with three unpaired nucleotide bases present. Each anticodon can bind temporarily with its complimentary codon.

Question 5

How are polypeptides assembled in translation?

Answer 5

1. A molecule of mRNA binds to a ribosome. two codons (or six bases) are attached to a small subunit of the ribosome and exposed to the large subunit. The first exposed mRNA codon is always AUG.
2. A second tRNA bearing a different amino acid binds to the second exposed codon with its complementary anticodon.
3. A peptide bond forms between the two adjacent amino acids, an enzyme present in the small ribosomal unit catalyses the reaction.
4. The ribosome now moves along the mRNA, reading the next codon. A third tRNA brings along the next amino acid, and the amino acid forms a peptide bond to the dipeptide. The first tRNA leaves and is able to pick up more amino acids.
5. The chain continues until a stop codon is reached.

Question 6

What is a mutation?

Answer 6

A change in the amount or arrangement of the genetic material in a cell.

Question 7

What is a substitution reaction?

Answer 7

Where one base pair replaces another.

Question 8

What are deletion/ insertion mutations?

Answer 8

Where one or more nucleotide pairs are inserted or deleted from a length of DNA.

Question 9

What is an allele?

Answer 9

An alternative version of a gene.

Question 10

Name all the parts of the lac operon and their functions.

Answer 10

The structural genes: Z codes for the enzyme B-galactosidase, and Y codes for the enzyme lactose permease.
The operator region: O, the length of DNA next to the structural genes. It can turn them on and off.
The promoter region: P, a length of DNA to which the enzyme RNA polymerise binds to in order to begin the transcription of the structural genes.