3 - Genetics - DNA

Question 1

What is DNA?

Answer 1

– A polymer made up of lots of nucleotides
– Two strands coiled together in a double helix, linked by complimentary base pairs which are joined by weak hydrogen bonds

Question 2

What are nucleotides in DNA?

Answer 2

— Consists of a sugar, a phosphate group and one base
— Sugar & phosphate groups form a ‘backbone’ to the DNA strands
— One of the four bases joins to each sugar

The sugar and phosphate groups alternate

Question 3

What are the Bases in DNA?

Answer 3

One of four different bases joins to each sugar:
Adenine
Thymine
Cytosine
Guanine

Question 4

What are complimentary base pairs?

Answer 4

Each base links to a base on the opposite strand in the helix:
A - T
C - G

Question 5

What is a genome?

Answer 5

All of an organisms DNA (including the non-coding regions) makes up it’s genome

Question 6

What is a gene?

Answer 6

A section of DNA on a chromosome that codes for a particular protein

Question 7

What is a Chromosome?

Answer 7

Long, coiled up molecules of DNA, found in the nucleus of eukaryotic cells

Question 8

How can you extract DNA from fruit? (P)

Answer 8

1) Mash strawberries & put into a beaker with a solution of detergent and salt & mix
• The detergent will break down the cell membranes to release DNA
• Salt makes DNA stick together
2) Filter the mix to get the froth & insoluble bits of cell out
3) Gently add ice cold alcohol to mixture
4) DNA will come out as it’s not soluble in cold alcohol. Will look like a stringy white precipitate

Question 9

How are proteins made in DNA?

Answer 9

• The order of the bases in a gene decide the order of amino acids in a protein
• Each amino acid will be coded for by a sequence of three bases in the gene (base triplet), then joined together to make proteins

Question 10

How can DNA make specifically shaped proteins?

Answer 10

Amino Acid chains fold up to give each protein a different, specific shape, meaning each protein can have a different function (like enzymes)

Question 11

What are the two stages of making proteins?

Answer 11

Transcription
Translation

Question 12

What are the first two stages of Transcription? (1&2)

Answer 12

1) RNA Polymerase binds to a region of non-coding DNA in front of a gene
2) The two DNA strands unzip and the RNA Polymerase moves along one of the strands of DNA

Question 13

What are the last two stages of Transcription? (3&4)

Answer 13

3) Base pairing ensures the mRNA made is complimentary to the gene
4) Once made, the mRNA molecule moves out of the nucleus and joins with a ribosome

Question 14

What are the first two stages of Translation? (1&2)

Answer 14

1) Amino Acids brought to the ribosome by transferRNA
2) Order that the amino acids brought matches the order of base triplets in mRNA (aka codons)

Question 15

What are the last two stages of Translation? (3&4)

Answer 15

3) Pairing of the Codon & Anticodon makes sure the amino acids are in the correct order
4) Amino Acids joined together by the ribosome, making a polypeptide (protein)

Question 16

What happens if there’s a mutation in the gene?

Answer 16

Produces a genetic variant - may code for a different sequence of amino acids & may change the shape & activity of the protein
This could end up changing the phenotype of an organism

phenotype = characteristics

Question 17

How do mutations in non-coding DNA affect RNA polymerase?

Answer 17

RNA polymerase has to bind to a region of DNA before transcription
If there is a mutation, it could affect the binding ability of RNAp

Question 18

How do mutations in non-coding DNA affect the protein?

Answer 18

How well RNAp binds to the region of DNA will affect how much mRNA is transcribed and how much protein is produced
Depending on the function of the protein, the phenotype may also be affected by how much is made