What are the two types of nitrogenous bases?
1) Pyramidines - one ring structure (C, T and U)
2) Purines - Two ring structure (G and A)
State three differences between DNA and RNA
DNA - Deoxyribose , ACGT, double stranded molecule
RNA - Ribose (extra oxygen at C2'), ACGU, single stranded molecule
What makes DNA chains polar?
Phosphate molecule at 5' end and hydroxyl group at 3'
What is a purine?
2 ring structure (hexagon and pentagon) - adenine and guanine
Describe the bonds found within and between chains of DNA in the double helix
Phosphodiester bonds between nucleotides to form sugar phosphate backbone of the double helix Hydrogen bonds form between complementary base pairs on opposite strands of the double helix
List the key features of the DNA double helix
- Antiparallel strands which are complimentary
- Bases on the inside of helix
- Deoxyribose and phosphate molecules on the outside of helix
What is a histone?
Positively charged protein molecule that helps to package DNA as negatively charged DNA molecules coil around the histone core to form a nucleosome giving the 'beads on a string' structure
What is a solenoid? When would it be found?
- 30nm fibre of densely coiled 'beads on a string'
- DNA found in this structure when it is not being expressed
Define a chromosome
Structure found in the cell nucleus containing one double stranded DNA molecule or two identical double stranded DNA molecules after DNA replication
Define the term gene
A unit of heredity, a length of DNA on a chromosome that contains the code for a protein to be transcribed
List the enzymes involved in DNA replication
DNA Helicase, primase, DNA polymerase, DNA ligase
How is DNA replication terminated?
Two replication forks meet and the leading and lagging strands of each template strand are joined by ligase
Why is the process of DNA replication termed semi-conservative?
Each strand of DNA from the parent molecules are conserved in the two daughter helices as each new helix produced contains one parent strand and one newly synthesised strand
Summarise the process of DNA replication
1) DNA helicase unwind the parental double helix
2) Single-strand binding proteins stabilise the unwound parental DNA
3) The leading strand is synthesised continuously in the 5' to 3' direction by DNA polymerase
4) The lagging strand is synthesised discontinuously. Primase synthesised a short RNA primer, which is extended by DNA polymerase to form an Okazaki fragment
5) After the RNA primer is replaced by DNA, DNA ligase joins the okazaki fragment to the growing strand
6) Replication is terminated when two replication forks meet and the leading and lagging strands of each template strand are joined by ligase
List the stages of the cell cycle
1) Interphase - G0, G1, S, G2
What is the purpose of G0?
Rest phase when cell either permanently (CNS) or temporarily leaves the cell cycle and stops dividing
List the differences between mitosis and meiosis
Mitosis - Produces two identical daughter cells, occurs in somatic cells, used for growth and repair of tissues, diploid cells produced
Meiosis - Creates genetic diversity by crossing over and independent assortment, used in spermatogenesis and oogenesis, haploid cells produced which maintains chromosome numbers
Name the process of producing egg cells
Define the terms genotype and phenotype
Genotype - genetic makeup of an individual
Phenotype - all observable characteristics of an individual as a result of the genetic makeup of one or more specific genetic locus or loci
List the environmental factors that can affect both genotype and phenotype
Chemicals that affect cell growth
What is meant by the term allele?
- An alternative form of a gene
- Each individual has two alleles for every gene which can either be the same or different (diploid organism)
Give an example of an X - linked genetic disease
What is complementation?
More than one gene is responsible for the phenotype Eg albinism
What can be said about two genes found on the same chromosomes?
Said to be 'linked', closer the loci of the genes, the more unlikely crossing over will occur
Explain the term dominance and give an example of an autosomal dominant disease
Phenotypic trait expressed in both heterozygous and homozygous so only one allele required in genotype for the trait to be expressed Eg huntingtons