Genome

Question 1

What is DNA?

Answer 1

A double-stranded polymer of
nucleotides, wound to form a double
helix

Question 2

What are the monomers of DNA?

Answer 2

Nucleotides

Question 3

What are DNA nucleotides made up of

Answer 3

● Common sugar
● Phosphate group
● One of four bases:A, T, C or G

Question 4

State the full names of the four bases found in

nucleotides

Answer 4

● Adenine
● Thymine
● Cytosine
● Guanine

Question 5

Describe how nucleotides interact to form a molecule of DNA

Answer 5

● Sugar and phosphate molecules join to form a sugar-phosphate backbone in each DNA strand
● Base connected to each sugar
● Complementary base pairs (A pairs with T, C pairs with G) joined by weak hydrogen bonds

Question 6

Define genome

Answer 6

The entire genetic material of an

organism

Question 7

What is a chromosome?

Answer 7

A long, coiled molecule of DNA that carries genetic information in the form of genes

Question 8

Define gene

Answer 8

A section of DNA that codes for a specific sequence of amino acids which undergo polymerisation to form a protein

Question 9

Describe the method used to extract DNA from fruit

Answer 9

1. Place a piece of fruit in a beaker and crush it
2. Add detergent and salt, mix
3. Filter the mixture and collect the liquid in a test tube
4. Pour chilled ethanol into the test tube
5. DNA precipitates forming white solid strands
6. Use a glass rod to collect the DNA sample

Question 10

Why is detergent added to the crushed fruit?

Answer 10

It disrupts the nuclear and cell membranes, releasing DNA into solution

Question 11

Why is salt added to the crushed fruit?

Answer 11

Salt encourages the precipitation of DNA

Question 12

Why is chilled ethanol added rather water?

Answer 12

DNA is insoluble in ethanol, encouraging its precipitation

Question 13

Explain how a gene codes for a protein

Answer 13

● Asequence of three bases in a gene forms a triplet
● Each triplet codes for an amino acid
● The order of amino acids determines the structure
(i.e. how it will fold) and function of protein formed

Question 14

Why is the ‘folding’ of amino acids important in

proteins such as enzymes?

Answer 14

The folding of amino acids determines the
shape of the active site which must be
highly specific to the shape of its substrate.

Question 15

What is protein synthesis?

Answer 15

The formation of a protein from a gene

Question 16

What are the two stages of protein synthesis?

Answer 16

1. Transcription

2. Translation

Question 17

What does transcription involve?

Answer 17

The formation of mRNA from a DNA

template

Question 18

Outline transcription

Answer 18

1. DNAdouble helix unwinds
2. RNApolymerase binds to a specific base sequence of non-coding
   DNAin front of a gene and moves along the DNA strand
3. RNApolymerase joins free RNAnucleotides to complementary bases
   on the coding DNA strand
4. mRNAformation complete. mRNAdetaches and leaves the nucleus.

Question 19

Describe the difference between mRNA and DNA

Answer 19

● mRNAis single stranded whereas
DNAis double stranded
● mRNAuses U whereas DNAuses T

Question 20

Why is mRNA used in translation rather than DNA?

Answer 20

DNAis too large to leave the nucleus so

cannot reach the ribosome.

Question 21

What does translation involve?

Answer 21

A ribosome joins amino acids in a
specific order dictated by mRNAto form
a protein.

Question 22

Outline translation

Answer 22

1. mRNAattaches to a ribosome
2. Ribosome reads the mRNA bases in triplets. Each triplet codes
   for one amino acid which is brought to the ribosome by a tRNA
   molecule
3. A polypeptide chain is formed from the sequence of amino
   acids which join together

Question 23

How is a tRNA molecule adapted to its function?

Answer 23

Each tRNA molecule has an anticodon
which is specific to the codon of the
amino acid that it carries.

Question 24

What is a mutation?

Answer 24

A random change in the base sequence

of DNA which results in genetic variants

Question 25

Describe the effect of a gene mutation in coding

DNA

Answer 25

● If a mutation changes the amino acid sequence,
protein structure and function may change
● If a mutation does not change amino acid sequence,
there is no effect on protein structure or function

Question 26

What is non-coding DNA?

Answer 26

DNA which does not code for a protein

but instead controls gene expression

Question 27

Describe the effect of a gene mutation in

non-coding DNA

Answer 27

● A mutation may affect the ability of RNA
polymerase to bind to non-coding DNA
● This may affect protein production and the
resulting phenotype of the organism

Question 28

Outline how the work of Mendel helped scientists to

develop their understanding of genetics

Answer 28

● Mendel studied the inheritance of different phenotypes of pea plants
● He established a correlation between parent and offspring phenotypes
● He noted that inheritance was determined by ‘units’ passed on to
descendants
● Using gene crosses, he devised the terms ‘dominant’ and ‘recessive’

Question 29

Why was Mendel’s work initially

overlooked?

Answer 29

Scientist’s didn’t understand Mendel’s
work as there was no knowledge of
genes or DNA at the time.