DNA structure, Protein Synthesis, Mutations, Alleles, Cystic fibrosis Flashcards
The DNA polymer is made up of ____________
The DNA polymer is made up of repeating nucleotide units.
How DNA determines the structure of proteins/ explain how the structure of DNA affects the protein made
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)
Each gene codes for ____
Each gene codes for one protein
How many different amino acids in humans
In humans there are twenty different amino acids
What determines the shape of the protein
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
What is the order of amino acids in a protein determined by
The order of amino acids in a protein is determined by the sequence of bases in the gene for that protein
What is the code for a particular amino acid
A sequence of three bases is the code for a particular amino acid.
What does the cell /ribosome read the DNA sequence as
The cell reads the DNA sequence as triplets of bases
e.g. ATG GGA CGC ATA
What does each triplet of base encode for
Each triplet encodes for a specific amino acid in the protein
ATG GGA CGC ATA
RED YELLOW BLUE GREEN
Describe the stages of protein synthesis
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
What is a mutation
A mutation is a change to a base
When can mutations occur
Mutations happen all the time
Explain why a mutation may not change the protein
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
Most mutations ________
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
Describe how a change in DNA structure may result in a change in the protein synthesised by a gene
Mutations changes its base sequence
This alters the amino acids that it codes for, which alters the shape of the protein.
A few mutations ___________
A few mutations code for an altered protein with a different shape
Describe the dramatic effects mutations may have on the function of a protein
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
Chromosomes also contain _______ parts of DNA
non-coding parts of DNA
What do the non-coding parts of DNA do
These regions switch genes on and off.
These regions tell genes when to produce proteins.
What happens if mutations occur in the non-coding parts/regions of DNA
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.
Where is DNA found
DNA is found in chromosomes
Normal human cells have 23 pairs of chromosomes what does this mean
This means that normal human cells contain two copies of every chromosome
Where do the chromosomes in a chromosome pair come from
One chromosome in the pair comes from your father
The other chromosome in the pair comes from your mother
Why do we have two copies of every gene
Because chromosome come in pairs, we have two copies of every gene
How are most characteristics controlled
Most characteristics are (a result of) controlled by many genes acting together e.g. height
Define Alleles
Alleles are versions of a gene
Define genotype
The genotype of a person tells us the alleles present
Someone’s genotype example
Someone’s phenotype example
Genotype: Ee, EE, ee
Phenotype: Dry Ear wax
Define homozygous
Where an organism has two alleles for a particular gene that are the same
Define heterozygous
Where an organism has two alleles for a particular gene that are different
Define phenotype
The phenotype of a person tells us characteristics caused by the person’s alleles
What is meant by a dominant allele
A dominant allele will show in the phenotype even if there is only one copy present
What is meant by a recessive allele
A recessive allele will only show in the phenotype if two copies are present (if no dominant allele is present)
Some characteristics are controlled by a ________
Some characteristics are controlled by a single gene
Explain why someone with the genotype EE is said to be homozygous
Because this person has two copies of the same allele
Phenotype of someone with ee
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
Phenotype of someone with Ee
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
Explain why someone with the genotype Ee is said to be heterozygous
Because this person has two different alleles
What is cystic fibrosis
Cystic fibrosis is a disorder of cell membranes
How many genes is cystic fibrosis controlled by
Cystic fibrosis is controlled by a single gene.
That gene has two alleles
Describe the alleles - regarding cystic fibrosis
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
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
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)
What is the genotype for someone who is a carrier of cystic fibrosis
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
What is cystic fibrosis caused by
Cystic fibrosis is a disorder caused by a recessive allele
Father - carrier cystic fibrosis
Mother - unaffected
Work out percentage of offspring who will be carriers and ratio between carriers and not affected
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
Cystic fibrosis
Father - carrier
Mother - carrier
Work out the genotype and the phenotype of the offspring and ratios
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
