Genetic code and chromosomes 8.1 - 8.2

Question 1

Define genetic code

Answer 1

The order/sequence of nucleotide bases in the mRNA that code for specific amino acids

Question 2

How many amino acids are there?

Answer 2

20

Question 3

How many triplet codes are there?

Answer 3

64

Question 4

Why is DNA ‘degenerative’?

Answer 4

Most amino acid are coded for by more than one triplet

Question 5

Why don’t all triplets code for amino acids?

Answer 5

3 act as punctuation marks/stop codes and indicate the end of a polypeptide chain

Question 6

What is the first amino acid coded for in any DNA sequence?

Answer 6

Methionine

Question 7

Why is genetic code ‘non-overlapping’?

Answer 7

Each base is read only once

Question 8

Why is genetic code ‘universal’?

Answer 8

Each triplet codes for the same amino acid in all living organisms
(this is indirect evidence for evolution)

Question 9

What is the term for a non-coding section of DNA?

Answer 9

An intron

Question 10

What is the term for a coding section of DNA?

Answer 10

An exon

Question 11

What is meant by the term ‘locus’

Answer 11

The position of a gene on a chromosome

Question 12

What is a gene?

Answer 12

A base sequence of DNA that codes for the amino acid sequence of a polypeptide or functional RNA

Question 13

Why doesn’t much of the DNA in eurkaryotes code for polypeptides?

Answer 13

• Many non-coding introns in DNA sequence

- Some genes code for ribosomal RNA and transfer RNAs

Question 14

What are the features of DNA in eurkaryotic cells that are not in prokaryotic cells?

Answer 14

• Associates with protein molecules called histones which allow DNA to fold up into chromosomes
• DNA is longer
• DNA is linear
• DNA is found in mitochondria and chloroplasts

Question 15

What are the features of DNA in prokaryotic cells that are not in eukaryotic cells?

Answer 15

• Does not associate with proteins
• Do not have chromosomes
• DNA is shorter
• DNA is circular

Question 16

What is meant by a bivalent/homologous pair?

Answer 16

Pair of chromosomes, one maternal and one paternal, that have the same gene loci and therefore determine the same characteristics

Question 17

When are chromosomes visible as distinct structures?

Answer 17

When the cell is dividing

Question 18

What is a chromatid?

Answer 18

One of the two strands of a chromosome that are joined together by a single centromere prior to cell division

Question 19

What is chromatin?

Answer 19

A material that makes up chromosomes. It consists of DNA and the protein histone

Question 20

How is DNA compacted into a chromosome?

Answer 20

• DNA combined with histones
• DNA-histone complex is coiled
• Coils fold to form loops
• Loops coil and pack together in the form of a chromosome

Question 21

How many molecules of DNA are held within 1 chromosome?

Answer 21

1

Question 22

How many chromosomes are there in a diploid cell?

Answer 22

46

Question 23

How many chromosomes are there in a haploid cell?

Answer 23

23

Question 24

What is an allele

Answer 24

One of a number of alternative forms of a gene