Section 3 - Genetics - DNA and protein synthesis

Question 1

Name the 4 different bases in DNA and the complementary base pairs?

Answer 1

A (adenine) + T (thymine), C (cytosine) + G (guanine)

Question 2

What is a DNA molecule made of and in the shape of?

Answer 2

Two strands coiled together in shape of a double helix.

Question 3

What are the complimentary base pairs joined together by?

Answer 3

Weak hydrogen bonds

Question 4

What are DNA strand polymers made up of? And what does each of this consist of?

Answer 4

Polymers made up of lots of repeating units called nucleotides, each one consisting of one sugar molecule, one phosphate molecule and one ‘base’

Question 5

What does the sugar and phosphate molecule in the nucleotides form? And which do bases join to?

Answer 5

Form a ‘backbone’ to DNA strands. Sugar and phosphate molecules alternate. One base joins to each sugar

Question 6

What are DNA stored as and contain what? Found where?

Answer 6

Stored as chromosomes and contain genes, found in nucleus of eukaryotic cells

Question 7

What is a gene?

Answer 7

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

Question 8

When extracting DNA from fruit cells, what do the detergent, salt and cold alcohol each do?

Answer 8

Detergent - break down cell membranes
Salt - make DNA stick together
Alcohol- DNA not soluble in cold alcohol so will appear

Question 9

What are proteins made up of and what does each different protein have?

Answer 9

Made up of chains of amino acids and each different protein has own particular number and order of amino acids, folding up to give a different, specific shape

Question 10

What decides the order of amino acids in a protein?

Answer 10

The order of the bases in a gene

Question 11

What is each amino acid coded for by?

Answer 11

Coded for by a sequence of three bases in gene called a base triplet, thus allowing gene to code for a particular protein

Question 12

What are non-coding regions found in many regions of DNA?

Answer 12

Means they don’t code for any amino acids

Question 13

What is a mutation?

Answer 13

A rare, random change to an organism’s DNA base sequence that can be inherited, causing a genetic variant

Question 14

What may a genetic variant cause? Example with enzyme

Answer 14

May code for a different sequence of amino acids, thus changing shape of final protein and so its activity.
Enzymes activity could change as they have specific active sites which catalyse a specific reaction

Question 15

Two main stages of protein synthesis and which one occurs first?

Answer 15

Transcription first then translation

Question 16

What is the structure of mRNA and what does the ‘m’ mean?

Answer 16

Messenger RNA, like DNA but shorter and only a single strand. Uses U (uracil) instead of T (thymine) as a base pairing with A (adenine)

Question 17

What is RNA polymerase?

Answer 17

Enzyme involved in joining together RNA nucleotides to make mRNA

Question 18

What happens in transcription of protein synthesis? 4 stages

Answer 18

• RNA polymerase binds to region of non-coding DNA in front of a gene
• two DNA strands unzip and RNA polymerase moves along one of strands of DNA
• uses coding DNA in gene as template to make mRNA, base paring between DNA and RNA ensures mRNA is complementary to gene
• once made, mRNA moves out of nucleus and joins with ribosome

Question 19

What happens in translation of protein synthesis?

Answer 19

• amino acids brought to ribosome by another RNA molecule called transfer RNA (tRNA)
• order in which amino acids brought to ribosome matches order of base triplets in mRNA (codons)
• pairing of codon and anticodon makes sure amino acid brought to ribosome in correct order
• amino acids joined together by ribosome, making polypeptide (protein)

Question 20

What are codons?

Answer 20

Base triplets in mRNA

Question 21

What is anticodon as part of structure of tRNA?

Answer 21

Complementary to codon for amino acid

Question 22

How will a mutation in the non-coding area affect how much protein is produced?

Answer 22

If mutation occurs here, could affect ability of RNA polymerase to bind to region, thus affecting how much mRNA is transcribed and therefore how much of protein is produced