4.1 DNA genes and chromosomes

Question 1

What is a gene

Answer 1

A base sequence of DNA that codes for a specific polypeptide or functional RNA

Question 2

What is the name given to the position of a particular gene on a chromosome

Answer 2

Locus

Question 3

What is an allele

Answer 3

Different form of a gene
e.g. eye colour

Question 4

How many alleles form one gene

Answer 4

2, one from father and one from mother

Question 5

List 3 differences between prokaryotic and eukaryotic DNA

Answer 5

• Prokaryotic DNA is circular whereas eukaryotic DNA is linear
• Eukaryotic DNA is associated with histone proteins whereas prokaryotic DNA isn’t
• Prokaryotic DNA is shorter than eukaryotic DNA

Question 6

How many chromosomes are in a human cell

Answer 6

46

Question 7

How are chromosomes formed

Answer 7

The DNA wraps around histone proteins, continuous coiling results in a supercoil and further folding results in a chromosome

Question 8

What does karyotype mean

Answer 8

The number and the type of chromosomes in a cell

Question 9

What are homologous chromosomes

Answer 9

2 chromosomes with the same genes in the same loci

Question 10

Can haploids have homologous chromosomes

Answer 10

No

Question 11

What is the genetic code

Answer 11

The sequence of bases in DNA

Question 12

If one base=one amino acid, what is the possible number of amino acids

Answer 12

4

Question 13

If 2 bases= one amino acid, what is the possible number of amino acids

Answer 13

16

Question 14

If 3 bases= one amino acid, what is the possible number of amino acids, and what does this show

Answer 14

64, there are only 20 naturally occurring amino acids therefore showing that some amino acids have multiple codes

Question 15

What are the 3 features of the genetic code

Answer 15

• Universal
• Degenerate
• Non-overlapping

Question 16

How is the genetic code universal

Answer 16

The triplet that codes for one amino acid in one organism will code for the same amino acid in all organisms

Question 17

How is the genetic code degenerate

Answer 17

Each triplet codes for a specific amino acid, many amino acids have more than one code

Question 18

How is the genetic code non-overlapping

Answer 18

Each base is only read once

Question 19

What are introns

Answer 19

Non-coding regions of DNA

Question 20

What are exons

Answer 20

Coding regions of DNA

Question 21

What type of DNA, eukaryotic or prokaryotic, contains introns

Answer 21

Eukaryotic

Question 22

In what process are the introns in DNA cut out

Answer 22

Protein synthesis

Question 23

What is a genome

Answer 23

The entire genetic code of an organism

Question 24

What is a proteome

Answer 24

The entire set of proteins that can be produced by the genome

Question 25

What does mRNA carry

Answer 25

The code for one gene

Question 26

Why can mRNA fit out of the nuclear pores but DNA cannot

Answer 26

Because mRNA only carries the code for one gene and is single stranded whereas DNA carries the genetic code for all genes and is double stranded so too large to fit through the pores

Question 27

What are the series of 3 consecutive bases called in DNA

Answer 27

A triplet

Question 28

What are the series of 3 consecutive bases called in mRNA

Answer 28

A codon

Question 29

What are the series of 3 consecutive bases called in tRNA

Answer 29

An anticodon

Question 30

What shape is the polynucleotide of mRNA

Answer 30

Helical

Question 31

What is the name of the process when mRNA copied from DNA

Answer 31

Transcription

Question 32

As mRNA is copied from DNA, what is complementary to what

Answer 32

mRNA's codons are complementary to DNA's triplets

Question 33

What is the shape of a tRNA molecule

Answer 33

Cloverleaf shape

Question 34

Is tRNA single or double stranded

Answer 34

Single

Question 35

How is the cloverleaf shape of a tRNA molecule held in place

Answer 35

By hydrogen bonds between the bases

Question 36

What is the function of tRNA

Answer 36

To transfer amino acids

Question 37

In a tRNA molecule what is the name of the 3 exposed bases at the top

Answer 37

The amino acid attachment site

Question 38

What is the function of rRNA

Answer 38

It combines with proteins to make ribosomes

Question 39

Describe how the appearance of the area containing DNA in a TEM image of a eukaryotic cell would differ from a prokaryotic cell (2 marks)

Answer 39

- Nucleus - Nucleolus - Mitochondria contain DNA

Question 40

Describe how a gene is a code for the production of a polypeptide. DO NOT include information about transcription and translation in your answer (3 marks)

Answer 40

- Because base sequence - In triplets - Determines sequence of amino acids/ primary structure in polypeptide

Question 41

Define the term exon (1 mark)

Answer 41

Base/ nucleotide/ triplet sequence coding for polypetide/ sequence of amino acids/ primary structure

Question 42

Define non-coding base sequences and describe where the non-coding multiple repeats are positioned in the genome (2 marks)

Answer 42

- DNA that does not code for a protein/ sequence of amino acids/ tRNA - Positioned between genes

Question 43

Give 5 ways in which chloroplast DNA is different from DNA in a nucleus

Answer 43

In chloroplasts - DNA is shorter - Fewer genes - DNA is circular not linear - Not associated with histones, unlike nuclear DNA - Introns absent but present in nuclear DNA