B13 Reproduction

Question 1

What is a gene?

Answer 1

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

Question 2

What is the shape of DNA called?

Answer 2

A double helix

Question 3

What is the genome

Answer 3

The entire genetic material of an organism

Question 4

What type of molecule is DNA?

Answer 4

A polymer

Question 5

What polymers make up DNA?

Answer 5

Nucleotides

Question 6

What are the 3 main parts of a nucleotide?

Answer 6

A phosphate group, attached to a sugar molecule, which is attached to a base

Question 7

Which part of the nucleotide changes, and which parts do not?

Answer 7

The base may vary, but the phosphate group and sugar molecule don’t change

Question 8

Name the 4 different bases

Answer 8

A,C,T and G

Question 9

“DNA strands are always complementary”, what does this phrase mean?

Answer 9

The same bases always pair on opposite strands

Question 10

What letters are linked to each other on DNA strands?

idk how to word this q

Answer 10

C is always linked to G

A is always linked to T

Question 11

What does the shape of a protein affect?

Answer 11

Its function

Question 12

What does the order of amino acids in a protein affect?

Answer 12

Its shape

Question 13

What controls the order of amino acids in a protein?

Answer 13

The sequence of bases in the gene for the protein

Question 14

How are nucleotides grouped?

Answer 14

Into groups of 3

Question 15

How many bases code for 1 amino acid?

Answer 15

Every group of 3 bases codes for 1 particular amino acid

Question 16

Name and explain the first stage of protein synthesis

Answer 16

Transcription, where the base sequence of the gene is copied into a complementary template molecule called Messenger RNA (MRNA). MRNA is a single stranded molecule. The MRNA then passes outside of the nucleus and into the cytoplasm

Question 17

Name and explain the second stage of protein synthesis

Answer 17

Translation, where the MRNA molecule attaches to a ribosome, and amino acids are brought to the ribosome on carrier molecules called Transfer RNA (TRNA). The ribosome reads the triplets of bases on the MRNA, and uses it to join the amino acids the correct order. Once the protein chain is complete, it folds into its correct shape and can perform its specific function

Question 18

What causes a mutation?

Answer 18

A change in a DNA base sequence

Question 19

What factors increase the risk of a mutation?

Answer 19

• Carcinogens

- Certain types of radiation (X-rays and Gamma rays)

Question 20

What is a triplet? (Codon)

Answer 20

A group of 3 bases

Question 21

How might a mutation affect an enzyme?

Answer 21

It could change the shape of its active site so the substrate doesn’t fit and the enzyme no longer works
(no longer forms an enzyme-substrate complex)

Or a new substrate could be able to fit so the enzyme catalyses a new reaction

Question 22

Why do most mutations not have a significant effect?

Answer 22

• They often only affect a protein very slightly

- They mostly occur in non coding DNA

Question 23

What is the purpose of non coding DNA?

Answer 23

To turn genes on and off

Question 24

What are the 3 types of mutations?

Answer 24

• Substitutions
• Insertions
• Deletions

Question 25

What happens in a substitution mutation?

Answer 25

One base is randomly swapped with another base

Question 26

What could be an affect of a substitution mutation?

Answer 26

It changes the codon that a base is in, which could change the amino acid that it codes for

Question 27

What happens in an insertion mutation?

Answer 27

A new base “inserts” itself into a sequence, pushing along a base to a new codon

e.g. ATG CTG ———– ACT GCT
|
C

Question 28

Why are insertion mutations damaging?

Answer 28

All subsequent bases after the insertion are moved along by one, changing each subsequent codon, making the amino acid chain produced significantly different

Question 29

What happens in a deletion mutation?

Answer 29

A base is deleted from a sequence, causing all subsequent bases to shift in the direction of the deleted base

Question 30

What is an allele?

Answer 30

One of two or more versions of a gene

Question 31

Where does each gene in a pair come from?

Answer 31

One gene comes from each parent

Question 32

What does the genotype of an person tell us?

Answer 32

The alleles present in them

Question 33

What does the phenotype of a person tell us?

Answer 33

The physical characteristics caused by their alleles

Question 34

What does it mean to be homozygous?

Answer 34

To have two copies of the same allele

Question 35

What does it mean to be heterozygous?

Answer 35

To have 2 different alleles

Question 36

What allele is shown in the phenotype when there are two different alleles present?

Answer 36

The dominant allele

Question 37

In what instance does a recessive allele show in the phenotype?

Answer 37

When there are two copies of the allele present

If no dominant allele is present

Question 38

Genes are small pieces of DNA. The DNA in a gene consists of a sequence of
bases.
Figure 2 shows part of the base sequence in the DNA of a normal haemoglobin gene
and the same section in the sickle-cell gene. A, C, G and T represent the different
bases.
Figure 2
Normal gene GGACTCCTC
Sickle-cell gene GGACACCTC
Describe how the mutation causes a change in the shape of the haemoglobin protein
molecule.

lol

Answer 38

three bases code for one amino acid

middle code of CTC is now CAC / T changed to A

so will be a different amino acid (in the chain)

(and so chain / protein will have a different shape) due to a different sequence
of amino acids