DNA structure, Protein Synthesis, Mutations, Alleles, Cystic fibrosis

Question 1

The DNA polymer is made up of ____________

Answer 1

The DNA polymer is made up of repeating nucleotide units.

Question 2

How DNA determines the structure of proteins/ explain how the structure of DNA affects the protein made

Answer 2

Proteins are made up from chains of amino acids

The order of amino acids in a protein is determined by the sequence of bases in the gene for that protein
A sequence of three bases is the code for a particular amino acid.

The specific order of amino acids determines the shape of the protein (and its function)
(The shape of the protein determines its function)

Question 3

Each gene codes for ____

Answer 3

Each gene codes for one protein

Question 4

How many different amino acids in humans

Answer 4

In humans there are twenty different amino acids

Question 5

What determines the shape of the protein

Answer 5

Importance of amino acids being in a specific order

The specific order of amino acids determines the shape of the protein (and its function)
The shape of the protein determines its function

Question 6

What is the order of amino acids in a protein determined by

Answer 6

The order of amino acids in a protein is determined by the sequence of bases in the gene for that protein

Question 7

What is the code for a particular amino acid

Answer 7

A sequence of three bases is the code for a particular amino acid.

Question 8

What does the cell /ribosome read the DNA sequence as

Answer 8

The cell reads the DNA sequence as triplets of bases
e.g. ATG GGA CGC ATA

Question 9

What does each triplet of base encode for

Answer 9

Each triplet encodes for a specific amino acid in the protein

ATG GGA CGC ATA
RED YELLOW BLUE GREEN

Question 10

Describe the stages of protein synthesis

Answer 10

Protein synthesis consists of two stages
The first stage takes place in the nucleus and the second stage takes place in the cytoplasm

The first stage is called transcription.
In this stage, the base sequence of the gene is copied into a complementary template molecule.
This template is called message RNA (or mRNA)
mRNA is a single stranded molecule
The mRNA now passes out of the nucleus and into the cytoplasm

The second stage of protein synthesis is called translation
In this stage, the mRNA molecule attaches to a ribosome.
Amino acids are now brought to the ribosomes on carrier molecules.
These carrier molecules are called transfer RNA (or tRNA)
The ribosome now reads the triplets of bases on the mRNA and uses this to join together the correct amino acids in the correct order.

Once the protein chain is complete, it now folds into its unique shape. The shape enables the protein to do its job as enzymes, hormones or forming structures in the body such as collagen

Question 11

What is a mutation

Answer 11

A mutation is a change to a base

Question 12

When can mutations occur

Answer 12

Mutations happen all the time

Question 13

Explain why a mutation may not change the protein

Answer 13

A mutation is a change to a base
A mutation might not change the amino acid sequence
This is because different base triplets can sometimes encode for the same amino acid.
Therefore in this case the mutation has had no effect on the protein’s shape or function

Question 14

Most mutations ________

Answer 14

Most mutations do not alter the protein, or
only alter it slightly so that its appearance or function is not changed.

Most mutations have no effect on the function of the protein

Question 15

Describe how a change in DNA structure may result in a change in the protein synthesised by a gene

Answer 15

Mutations changes its base sequence
This alters the amino acids that it codes for, which alters the shape of the protein.

Question 16

A few mutations ___________

Answer 16

A few mutations code for an altered protein with a different shape

Question 17

Describe the dramatic effects mutations may have on the function of a protein

Answer 17

The active site of an enzyme may change shape, so it can no longer bind to the substrate.
If a mutation changes the shape of a structural protein such as collagen, then it may lose its strength

Question 18

Chromosomes also contain _______ parts of DNA

Answer 18

non-coding parts of DNA

Question 19

What do the non-coding parts of DNA do

Answer 19

These regions switch genes on and off.
These regions tell genes when to produce proteins.

Question 20

What happens if mutations occur in the non-coding parts/regions of DNA

Answer 20

Mutations in these non-coding regions can affect how genes are switched on or off
E.g. a gene may be turned on when it should be turned off
In this case, the cell would produce a protein that is not meant to have at that time
This could have a very significant effect on a cell e.g. uncontrolled mitosis leading to cancer

Not all parts of DNA code for proteins. Non-coding parts of DNA can switch genes on and off, so variations in these areas of DNA may affect how genes are expressed.

Question 21

Where is DNA found

Answer 21

DNA is found in chromosomes

Question 22

Normal human cells have 23 pairs of chromosomes what does this mean

Answer 22

This means that normal human cells contain two copies of every chromosome

Question 23

Where do the chromosomes in a chromosome pair come from

Answer 23

One chromosome in the pair comes from your father
The other chromosome in the pair comes from your mother

Question 24

Why do we have two copies of every gene

Answer 24

Because chromosome come in pairs, we have two copies of every gene

Question 25

How are most characteristics controlled

Answer 25

Most characteristics are (a result of) controlled by many genes acting together e.g. height

Question 26

Define Alleles

Answer 26

Alleles are versions of a gene

Question 27

Define genotype

Answer 27

The genotype of a person tells us the alleles present

Question 28

Someone’s genotype example
Someone’s phenotype example

Answer 28

Genotype: Ee, EE, ee
Phenotype: Dry Ear wax

Question 29

Define homozygous

Answer 29

Where an organism has two alleles for a particular gene that are the same

Question 30

Define heterozygous

Answer 30

Where an organism has two alleles for a particular gene that are different

Question 31

Define phenotype

Answer 31

The phenotype of a person tells us characteristics caused by the person’s alleles

Question 32

What is meant by a dominant allele

Answer 32

A dominant allele will show in the phenotype even if there is only one copy present

Question 33

What is meant by a recessive allele

Answer 33

A recessive allele will only show in the phenotype if two copies are present (if no dominant allele is present)

Question 34

Some characteristics are controlled by a ________

Answer 34

Some characteristics are controlled by a single gene

Question 35

Explain why someone with the genotype EE is said to be homozygous

Answer 35

Because this person has two copies of the same allele

Question 36

Phenotype of someone with ee

Answer 36

This person has two copies of the alleles for dry ear wax
Because there is no dominant allele present, their phenotype is dry ear wax

Question 37

Phenotype of someone with Ee

Answer 37

This person has one allele for dry ear wax and one allele for wet ear wax
The allele for wet ear wax is dominant to the allele for dry ear wax
A dominant allele is always expressed (even if only one copy is present)
Therefore, because the allele for wet ear wax is dominant their phenotype is wet ear wax

Question 38

Explain why someone with the genotype Ee is said to be heterozygous

Answer 38

Because this person has two different alleles

Question 39

What is cystic fibrosis

Answer 39

Cystic fibrosis is a disorder of cell membranes

Question 40

How many genes is cystic fibrosis controlled by

Answer 40

Cystic fibrosis is controlled by a single gene.
That gene has two alleles

Question 41

Describe the alleles - regarding cystic fibrosis

Answer 41

The allele for normal cell membrane function is dominant. This allele has the symbol C

The allele for defective cell membranes is recessive.
This has the symbol c

Question 42

The allele for normal cell membrane function is dominant. This allele has the symbol C

The allele for defective cell membranes is recessive.
This has the symbol c

What does this mean, in order for someone to have cystic fibrosis

Answer 42

In order to have cystic fibrosis, the person has to have two copies of the defective allele (they have to inherit a defective allele from both of their parents)

Question 43

What is the genotype for someone who is a carrier of cystic fibrosis

Answer 43

A person with one defective allele and one normal allele does not have cystic fibrosis.
They are a carrier of the cystic fibrosis allele
Cc

Question 44

What is cystic fibrosis caused by

Answer 44

Cystic fibrosis is a disorder caused by a recessive allele

Question 45

Father - carrier cystic fibrosis
Mother - unaffected
Work out percentage of offspring who will be carriers and ratio between carriers and not affected

Answer 45

ratio between carriers and not affected = 1:1

On average, 50% of the offspring will be carriers and 50% will be unaffected
Remember: Because these are just probabilities, it is possible that all of the offspring could be carriers, or all of the offspring could be unaffected

Father
C c
mother
C

C

The letters represent the gametes.
Half of the male gametes will have the cystic fibrosis allele
Half of the male gametes will have the normal allele

All of the female gametes will have the normal allele

Question 46

Cystic fibrosis
Father - carrier
Mother - carrier
Work out the genotype and the phenotype of the offspring and ratios

Answer 46

CC Cc Cc cc
25% of offspring will be homozygous dominant - unaffected (homozygous for the capital C allele)

50% of offspring will be heterozygous - carriers of the cystic fibrosis allele

25% of offspring will be homozygous recessive (homozygous for the lower case c allele) these offspring have cystic fibrosis -

1:4 unaffected
2:4 carriers
1:4 with cystic fibrosis