Genetic Control of protein structure and function

Question 1

What is a degenerate code?

Answer 1

More than one codon codes for one amino acid.

Question 2

What is a stop codon?

Answer 2

A codon that doesn’t code for any amino acids. There are three stop codons and they mark the end of a polypeptide chain.

Question 3

What is a universal code?

Answer 3

The same codon codes for the same amino acid in all organisms (with a few minor exceptions).

Question 4

What is a nucleotide made of?

Answer 4

Pentose sugar ribose
One of the organic bases (ATGC)
A phosphate group

Question 5

What type of RNA are important in protein synthesis?

Answer 5

Messenger RNA (mRNA)
Transfer RNA (tRNA)

Question 6

Describe the structure of mRNA.

Answer 6

Long strand
Arranged in a single helix
Consists of organic bases that code for a specific polypeptide

Question 7

Describe the structure of tRNA.

Answer 7

Single stranded

Folded chain into a clover shape.

Question 8

What are exons?

Answer 8

Sections of DNA that code for a polypeptide.

Question 9

What are introns?

Answer 9

Sections of DNA that do not code for a polypeptide.

Question 10

What is transcription?

Answer 10

The formation of mRNA molecules from the DNA that makes up a particular gene. It is the first stage of protein synthesis.

Question 11

How does transcription happen?

Answer 11

1. DNA helicase acts on a specific region of the DNA molecule to break the hydrogen bonds between the bases, causing the two strands to separate and expose the nucleotide bases in that region.
2. RNA polymerase moves along one of the two DNA strands known as the template strand, causing the nucleotides on this strand to join with individual complementary nucleotides from the pool which is present in the nucleus.
3. Thymine binds to adenine
   Adenine binds to Uracil
   Guanine to Cytosine and vice versa
4. Strand of pre-mRNA is built one at a time as the nucleotides are added one at a time. The DNA strands rejoin behind it adn so only about 12 base pairs on the DNA are exposed at any one time.
5. The production of pre-mRNA is complete when the RNA polymerase reaches a certain sequence, a stop codon.

Question 12

What is the splicing of pre-mRNA?

Answer 12

The introns are removed from the strand

Question 13

Why can a single section of DNA code for up to a dozen different protein?

Answer 13

The exons can be joined up after splicing in a different order.

Question 14

Summarise the complete process of polypeptide synthesis.

Answer 14

1. DNA provides the instructions in the form of a long sequence of nucleotides and the bases they possess.
2. A complementary section of part of this sequence is made in the form of a molecule called pre-mRNA. This is transcription.
3. The pre-mRNA is moodified to mRNA by removing the base sequence coped from introns, this is called splicing.
4. The mRNA is used as a template to which complementary tRNA molecules attach and the amino acids they carry are linked to form a polypeptide. This is called translation.