B13 Reproduction Flashcards
What is a gene?
A small section of DNA on a chromosome that codes for a protein
What is the shape of DNA called?
A double helix
What is the genome
The entire genetic material of an organism
What type of molecule is DNA?
A polymer
What polymers make up DNA?
Nucleotides
What are the 3 main parts of a nucleotide?
A phosphate group, attached to a sugar molecule, which is attached to a base
Which part of the nucleotide changes, and which parts do not?
The base may vary, but the phosphate group and sugar molecule don’t change
Name the 4 different bases
A,C,T and G
“DNA strands are always complementary”, what does this phrase mean?
The same bases always pair on opposite strands
What letters are linked to each other on DNA strands?
idk how to word this q
C is always linked to G
A is always linked to T
What does the shape of a protein affect?
Its function
What does the order of amino acids in a protein affect?
Its shape
What controls the order of amino acids in a protein?
The sequence of bases in the gene for the protein
How are nucleotides grouped?
Into groups of 3
How many bases code for 1 amino acid?
Every group of 3 bases codes for 1 particular amino acid
Name and explain the first stage of protein synthesis
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
Name and explain the second stage of protein synthesis
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
What causes a mutation?
A change in a DNA base sequence
What factors increase the risk of a mutation?
- Carcinogens
- Certain types of radiation (X-rays and Gamma rays)
What is a triplet? (Codon)
A group of 3 bases
How might a mutation affect an enzyme?
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
Why do most mutations not have a significant effect?
- They often only affect a protein very slightly
- They mostly occur in non coding DNA
What is the purpose of non coding DNA?
To turn genes on and off
What are the 3 types of mutations?
- Substitutions
- Insertions
- Deletions
What happens in a substitution mutation?
One base is randomly swapped with another base
What could be an affect of a substitution mutation?
It changes the codon that a base is in, which could change the amino acid that it codes for
What happens in an insertion mutation?
A new base “inserts” itself into a sequence, pushing along a base to a new codon
e.g. ATG CTG ———– ACT GCT
|
C
Why are insertion mutations damaging?
All subsequent bases after the insertion are moved along by one, changing each subsequent codon, making the amino acid chain produced significantly different
What happens in a deletion mutation?
A base is deleted from a sequence, causing all subsequent bases to shift in the direction of the deleted base
What is an allele?
One of two or more versions of a gene
Where does each gene in a pair come from?
One gene comes from each parent
What does the genotype of an person tell us?
The alleles present in them
What does the phenotype of a person tell us?
The physical characteristics caused by their alleles
What does it mean to be homozygous?
To have two copies of the same allele
What does it mean to be heterozygous?
To have 2 different alleles
What allele is shown in the phenotype when there are two different alleles present?
The dominant allele
In what instance does a recessive allele show in the phenotype?
When there are two copies of the allele present
If no dominant allele is present
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
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
