Gene Expression

Question 1

What controls a cell’s phenotype (Its physical state) ?

Answer 1

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

Question 2

What controls gene expression

Answer 2

Gene expression is controlled by transcription and translation, only a fraction of the genes in a cell are expressed.

Question 3

What are the repeating units of RNA called?

Answer 3

RNA nucleotides

Question 4

Describe the structure of an RNA nucleotide

Answer 4

-Ribose sugar (5 carbons and 1 oxygen, arranged in a pentagon with an oxygen top and a carbon 5 tail extending upwards from carbon 4 )
-A base ( A/U/C/G) is connected to carbon 1
-A phosphate is connected to carbon 5

(RNA is called ribonucleic acid)

Question 5

What are the names of the four RNA bases?

Answer 5

Adenine, Cytosine, Guanine and Uracil

Question 6

What are the three types of RNA?

Answer 6

-mRNA (messenger RNA)
-tRNA (transfer RNA)
-rRNA (Ribosomal RNA)

Question 7

What is the role of mRNA?

Answer 7

mRNA carries a complimentary copy of the DNA code from the nucleus to a ribosome.

Question 8

What is the role of tRNA?

Answer 8

Carries a specific amino acid from the cytoplasm to a ribosome (Amino acids in cytoplasm from food)

Question 9

Describe the structure of a tRNA molecule

Answer 9

-Forms a t or a + shape as it folds due to complementary base pairing, to become more stable as the cytoplasm is a harsh environment, which gives it its shape.
- Amino acid attachment site at its 3’ end, anticodon on the bottom (open three bases)

Question 10

Describe 4 differences between DNA and RNA

Answer 10

DNA has two strands, is found in the nucleus, contains a deoxyribose sugar and its organic bases are adenine, thymine, cytosine and guanine.
RNA has one strand, is found in the nucleus, cytoplasm and ribosome, contains a ribose sugar and its organic bases are adenine, uracil, guanine and cytosine.

Question 11

What is transcription?

Answer 11

Transcription is the process by which the DNA base sequence is transcribed into mRNA, in the nucleus.

Question 12

What is the triplet code and codon?

Answer 12

On DNA, a triplet code is a set of three bases which codes for one amino acid, on mRNA, these base triplets are known as codons.

Question 13

What is the function of rRNA?

Answer 13

Binds with a protein molecule to form a ribosome.

Question 14

What are the stages of transcription

Answer 14

1) RNA polymerase moves along the DNA, unwinding the double helix and unzipping the hydrogen bonds between bases.
2) RNA polymerase adds complementary RNA nucleotides to the template strand of DNA to synthesize a primary mRNA transcript.
3) The primary mRNA transcript moves away from the DNA.

Question 15

What are the requirements for transcription?

Answer 15

1) Original DNA templates
2) Supply of RNA Nucleotides.
3) RNA polymerase
4) Energy (ATP)

Question 16

What is RNA splicing?

Answer 16

RNA splicing forms a mature transcript from the primary mRNA transcript.
-The introns are removed from the primary transcript of mRNA.
-The exons are joined together to form a mature mRNA transcript.
-The order of exons is unchanged during splicing.

Question 17

What are introns and exons?

Answer 17

Introns = non-coding regions (of DNA or RNA) that are removed by RNA splicing
Exons + coding regions (of DNA or RNA) that are required for protein synthesis, retained during RNA splicing.

Question 18

What is translation

Answer 18

Translation is the process where tRNA translates mRNA into a polypeptide at the ribosome, in the cytoplasm.

Question 19

What are the requirements for translation.

Answer 19

1) Mature mRNA transcripts.
2) Supply of amino acids.
3) Energy (ATP)

Question 20

What are stop and start codons ?

Answer 20

Translation beings at a start codon (AUG, 5’ of mature mRNA)
Translation ends at a stop codon.

Question 21

What are the stages of translation ?

Answer 21

1) A ribosome binds to the 5’ ends of the mature mRNA template at the mature mRNA’s start codon (5’ end)
2) Each molecule of tRNA carries a specific amino acid from the cytoplasm to the ribosome.
3) Codons on mRNA and anticodons on tRNA bind together using complementary base pairing.
4) The ribosome moves along the mRNA transcript, translating the genetic code into a sequence of amino acids - the order of codons on the mRNA determines the sequence of amino acids.
5) A peptide bond forms between the adjacent amino acids, to forma polypeptide chain.
6) tRNA molecule is removed from the ribosome as the polypeptide forms.
7) This process continues until a stop codon is reached

Question 22

What is alternative RNA splicing?

Answer 22

-Allows for different proteins to be produced from one gene, by producing different mature mRNA molecules from the same primary transcript. This depends on which exons ae retained.

Question 23

What controls a protein’s three dimensional shape?

Answer 23

-The polypeptide chain folds to form the three dimensional shape of a protein.
-Hydrogen bonds and other interactions between individual amino acids hold the protein in its three dimensional shape.

Question 24

What determines the shapes of proteins?

Answer 24

The order of DNA bases determines the order of amino acids, this determines the structure and function of the protein.

Proteins have a large variety of shapes, which determines their functions;

Structural
Hormones
Antibodies S.H.A.P.E
Receptors
Enzymes

Question 25

How do environmental factors affect phenotype?

Answer 25

Environmental factors influence phenotype by changing the order of the base sequence.
Some examples of environmental factors include: UV radiation, Nuclear radiation, mustard gas and x-rays.