8.1- GENES AND THE GENETIC CODE

Question 1

What is a gene?

Answer 1

section of DNA that contains coded information for making polypeptide + functional RNA

Question 2

What is the coded information in the form of in a gene?

Answer 2

specific sequence of bases along DNA molecule

Question 3

What do polypeptides make up?

Answer 3

proteins

Question 4

As polypeptides make up proteins, what do genes determine?

Answer 4

genes determine proteins of organism

Question 5

What are enzymes an example of?

Answer 5

proteins

Question 6

What do enzymes control?

Answer 6

control chemical reactions

Question 7

As enzymes control chemical reactions, what are they responsible for?

Answer 7

organism’s development + activities

Question 8

What determines the nature + development of all organisms?

Answer 8

genes + environmental factors

Question 9

What is the particular position of a gene on a section of DNA called?

Answer 9

locus

Question 10

What can a gene code for? (2)

Answer 10

amino acid sequence of polypeptide
or
functional RNA, including ribosomal RNA + transfer RNAs

Question 11

How many genes does one DNA molecule carry?

Answer 11

carries many genes

Question 12

Why did scientists suggest there must be a minimum of three bases that codes for each amino acid: number of amino acids?

Answer 12

only 20 different amino acids regularly occur in proteins

Question 13

Why did scientists suggest there must be a minimum of three bases that codes for each amino acid: what each amino acids must have?

Answer 13

each amino acid must have its own code of bases on DNA

Question 14

Why did scientists suggest there must be a minimum of three bases that codes for each amino acid: number of bases?

Answer 14

only 4 different bases (adenine, guanine, cytosine + thymine) present in DNA

Question 15

Why did scientists suggest there must be a minimum of three bases that codes for each amino acid: what if each base coded for a different amino acid?

Answer 15

if each base coded for a different amino acid, only 4 different amino acids could be coded for

Question 16

Why did scientists suggest there must be a minimum of three bases that codes for each amino acid: what if a pair of bases were used for an amino acid?

Answer 16

using pair of bases, 16 (4^2) different codes possible, which is still inadequate

Question 17

Why did scientists suggest there must be a minimum of three bases that codes for each amino acid: what if three bases were used for an amino acid?

Answer 17

three bases produces 64 (4^3), more than enough to satisfy requirements of 20 amino acids

Question 18

As the code has three bases for each amino acid, what is each one called?

Answer 18

a triplet

Question 19

As there are 64 possible triplets and only 20 amino acids, what follows?

Answer 19

some amino acids coded for by more than one triplet

Question 20

What are a few amino acids coded for by?

Answer 20

only a single triplet

Question 21

What are most of the amino acids coded for by?

Answer 21

between two and six triplets each

Question 22

Why is the code known as a ‘degenerate code’?

Answer 22

most amino acids coded for by more than one triplet

Question 23

How is a triplet always read?

Answer 23

in one particular direction along the DNA strand

Question 24

What is the start of a DNA sequence always?

Answer 24

code for polypeptide always same triplet

Question 25

What does the start the DNA sequence triplet code for?

Answer 25

amino acid methionine

Question 26

What happens if the first methionine molecules doesn't form part of the final polypeptide?

Answer 26

it's later removed

Question 27

What do three triplets that do not code for an amino acid called?

Answer 27

'stop codes'

Question 28

What do 'stop codes' mark?

Answer 28

end of polypeptide chain

Question 29

What does it mean that the code is non-overlapping?

Answer 29

each base in sequence read only once

Question 30

What does it mean the code is universal?

Answer 30

with a few minor exceptions each triplet codes for same amino acid in all organisms

Question 31

What is the code being universal indirect evidence for?

Answer 31

evolution

Question 32

What does much of the DNA in eukaryotes not do?

Answer 32

do not code for polypeptides

Question 33

What are coding sequences called?

Answer 33

exons

Question 34

What are non-coding sequences called?

Answer 34

introns

Question 35

What do some genes code for?

Answer 35

ribosomal RNA + transfer RNAs