KA3 - Gene Expression

Question 1

What is gene expression?

Answer 1

Gene expression involves the transcription and translation of DNA sequences

Question 2

What is an RNA nucleotide composed of?

Answer 2

A ribose sugar

A phosphate group

One of the 4 bases (adenine, thymine, cytosine, guanine)

Question 3

What are the 3 types of RNA?

Answer 3

mRNA (messenger RNA)

rRNA (ribosomal RNA)

tRNA (transfer RNA)

Question 4

What is the function of mRNA?

Answer 4

mRNA is transcribed from DNA in the nucleus and translated into proteins by ribosomes in the cytoplasm

Each triplet of bases on the mRNA molecule is called a codon and codes for a specific amino acid

Question 5

What is the function of rRNA?

Answer 5

rRNA, along with proteins forms the ribosome

The ribosome is the site of protein synthesis

Question 6

Describe the structure of tRNA

Answer 6

tRNA has a folded shape due to complimentary base pairing

The bases of tRNA are held together by weak hydrogen bonds

A tRNA molecule has an anticodon(an exposed triplet of bases) at one end and an attachment side for a specific amino acid at the other end

Question 7

What is the function of tRNA?

Answer 7

The role of tRNA is to carry its specific amino acid to the ribosome

Question 8

Define protein synthesis

Answer 8

Protein synthesis is the process by which instructions from DNA sequences are carried to ribosomes and proteins are made.

Question 9

What is the first stage of protein synthesis?

Answer 9

Transcription

Question 10

What is transcription?

Answer 10

Transcription is the process by which mRNA is transcribed from DNA

Question 11

What is the first stage of transcription?

Answer 11

1. The enzyme RNA polymerase moves along DNA, unwinding the double helix and breaking the hydrogen bonds between the bases thereby unzipping the double helix

Question 12

What is the second stage of transcription?

Answer 12

2. As RNA polymerase breaks the bonds, it synthesises a primary transcript of mRNA on the DNA template strand using free RNA nucleotides. These RNA nucleotides form hydrogen bonds with the exposed DNA bases by complimentary base pairing

Question 13

What is the third stage of transcription?

Answer 13

3. A primary mRNA transcript is formed

Question 14

What two components is the primary transcript made of?

Answer 14

Introns and exons

Question 15

What are introns?

Answer 15

Introns are regions of the primary transcript of mRNA which are non-coding

Question 16

What are exons?

Answer 16

Exons are coding regions of the primary transcript of mRNA

Question 17

What happens during splicing?

Answer 17

The introns are removed from the primary transcript

The exons are then joined together to form the mature transcript

Question 18

What is the mature transcript?

Answer 18

The mature transcript leaves the nucleus through a pore in the nuclear membrane

The mature transcript travels through the cytoplasm to a ribosome for the next stage of protein synthesis

Question 19

What is the second stage of protein synthesis?

Answer 19

Translation

Question 20

What is translation?

Answer 20

Translation is the synthesis of a polypeptide chain under the direction of mRNA at the ribosome

Question 21

What happens during translation?

Answer 21

Translation begins at a start codon and ends at a stop codon

Anti codons bond to codons by complimentary base pairing, translating the genetic code into a sequence of amino acids

Peptide bonds join the amino acids together

Each tRNA then leaves the ribosome as the polypeptide is formed

tRNA has an anticodon and amino acid attachment side

Question 22

What can happen as a result of alternative RNA splicing?

Answer 22

Different proteins can be expressed from one gene, as a result of alternative RNA splicing

Question 23

What happens depending on which exons are retained?

Answer 23

Different mature mRNA transcripts are produced from the same primary transcript depending on which exons are reatined

Question 24

What are amino acids linked by and what does this form?

Answer 24

Amino acids are linked by peptide bonds to form polypeptides

Question 25

What do polypeptide chains fold to form?

Answer 25

Polypeptide chains fold to form the three dimensional shape of a protein, held together by hydrogen bonds and other interactions between individual amino acids

Question 26

What determines a proteins function?

Answer 26

Proteins have a large variety of shapes which determine their functions

Question 27

What is phenotype determined by?

Answer 27

Phenotype is determined by the proteins produced as the result of gene expression