2C Flashcards
Summarise the process of DNA replication.
“1. Double helix unwinds and the hydrogen bonds break, catalysed by DNA helicase.
2. Complementary base pairing occurs between the two template strands and free DNA nucleotides.
3. The nucleotides are joined in a condesation reaction by phosphodiester bonds, catalysed by DNA polymerase. “
Why is DNA replication considered semi-conservative?
The new DNA molecule consists of one new and one orginal polynucleotide strand.**
Explain how experimental data has supported the theory of DNA replication..
Meselson and Stahl: allowed bacteria conntainig DNA made from heavy nitrogen to replicate once with light nitrogen. The resulting DNA molecules had one strand containing the original heavy DNA and one containing the new light DNA- shows that replication is semi conservative.
What is a mutation?
A change in the DNA base sequence. Often arise spontaneously during DNA replication.
Define the five types of mutation
Substitution, deletion, duplication, insertion, inversion
Define insertion mutation
A base is added in the sequence shifting the reading frame along one
Define deletion mutation
A base is deleted in the sequence shifting the reading frame back one
Define duplication mutation
A base is duplicated in the sequence shifting the reading frame along one
Define inversion mutation
Two bases are swapped. No affect on other triplet codes.
Define substitution mutation
One base is swapped for another base. No affect on other triplet codes.
How might a mutation lead to a different protein formed?
Change in base sequence in DNA, change in amino acid sequence, different R groups means different bonds in the tertiary structure of the protein, different folding and 3D shape of the protein formed
Define genotype.
The alleles present
Define phenotype.
The expression of an organism’s genotype, combined with its interaction with the environment
What is an allele?
Different forms of a particular gene, found at the same locus (position) on a chromosome with a slightly different base sequence.
What is meant by a dominant allele?
An allele whose characteristic will always appear in the phenotype, whether one or two are present.
What is meant by a recessive allele?
An allele whose characteristic only appears in the phenotype if no dominant allele is present.
What is meant by incomplete dominance?
An allele whose characteristic is not completely expressed over its paired recessive allele. The result is a phenotype that is a combination of the two alleles.
What is meant by homozygous and heterozygous?
“Homozygous = both alleles are dominant, or both alleles are recessive.
Heterozygous = one allele is dominant, the other is recessive.”
Define monohybrid inheritance.
Where one phenotypic characteristic is controlled by a single gene with various alleles
Give an example of a disorder that arises from a mutation.
Cystic fibrosis.
How is functioning impaired in people with cystic fibrosis?
“● Respiratory=mucus in lungs reduces surface area for gas exchange and traps harmful bacteria.
● Digestive=nutrients not properly absorbed due to thick mucus covering intestine lining.
● Reproductive=mucus prevents sperm from reaching egg (in women) and blocks the sperm duct (in men).”
Explain the symptoms of cystic fibrosis
CFTR protein mutation means Chloride ions not transported out of the cell so solute concentration remains low and water does not follow by osmosis leading to thick mucus prodcution as the mucus is not watered down.
What is meant by genetic screening?
Determining if an individual’s DNA contains a certain allele (often by blood sample), usually one that may result in a genetic disorder.
Describe the process of chorionic villus sampling.
A sample of embryonic tissue is taken from the placenta at around 11 to 14 weeks of pregnancy. Screened for various disorders, and results are available quickly.
