Define gene, allele, locus and chromosome.
Gene: a section of DNA that codes for a polypeptide and RNA.
Allele: alternative version of a gene
Locus: location of a particular gene on a chromosome
Chromosome: tightly coiled up DNA, located in the nucleus. 23 pairs of chromosomes, 46 total
Define homologous pairs
A pair of matching chromosomes with the same genes and are the same size (but might have different alleles).
How is DNA stored?
Stored as chromosomes in the nucleus. The DNA is tightly coiled around histone proteins to fit inside (nucleosome). Eukaryotic DNA is linear.
How does prokaryotic DNA differ from eukaryotic DNA.
Shorter, circular and not wound around histone proteins.
Describe structure of eukaryotic and prokaryotic DNA.
Short, circular and not histone-bound.
What is the start/stop codon?
Start: the 3 bases at start of gene that initiates translation
Stop: 3 bases at end of gene that marks end of polypeptide chain so ribosomes detach and translation stops.
Describe degenerate feature of DNA, how is this advantageous?
Each of the 20 amino acids can be coded for by more than one triplet base this means mutations will potentially have no effect.
How is DNA universal? How is this advantageous?
The same triplet of bases code for the same amino acid in all organisms, allows genetic engineering.
How is DNA not over-lapping? How is this advantageous?
Each base in a gene is only part of one codon that codes for one amino acid. If a mutation occurs it will only effect one amino acid.
Define introns and exons
Introns: Sections of DNA that don’t code for an amino acid or polypeptide chains. Only found in eukaryotic DNA. They are spliced and removed from pre-mRNA.
Exons: sections of DNA that do code for amino acids.
Define genome and proteome
Genome: an organism’s complete set of DNA in one cell. The genome of organisms differ largely.
Proteome: full range of proteins in one cell.
Genome should never change whilst proteome is constantly changing depending on what proteins are needed.
Describe product of translation.
Complementary mRNA copy of one gene on DNA is created in nucleus. mRNA is much shorter than DNA so it can fit through nuclear pores and carry genetic code to ribosome for protein synthesis.
Describe process of transcription.
Occurs in nucleus.
H bond between DNA bases break so double helix separates and template strand is exposed. Only one DNA strand acts as a template for the formation of RNA. Free RNA nucleotides align by complimentary base pairing to the exposed bases on the DNA template strand. In RNA uracil base pairs with adenine on DNA strand. RNA polymerase catalyses condensation reaction between adjacent RNA nucleotides to form phosophodiester bonds and creasting sugar-phosphate backbone.
Once copied mRNA is spliced and exits via nuclear pores.
Describe process of splicing.
After transcription, pre-MRNA is spliced to remove introns and join exons together to form mRNA.
Describe process of translation.
mRNA attaches to ribosome in cytoplasm. Ribosome reads codon sequence on mRNA and tRNA molecule with anticodon complimentary to codon on mRNA binds to it by complimentary base pairing at start codon. Each tRNA molcule carries a specific amino acid. Ribosome joins amino acids carried by tRNA with peptide bond which requires ATP. Ribosome moves along mRNA to next codon and process repeats until stop codon is reached nd polypeptide chain is released (Polypeptide chain can then enter golgi for modifications and folding).
What is meiosis and what is the product?
Meiosis is a type of nuclear division and creates 4 genetically different haploid cells from a single diploid parent.
Describe 3 ways to introduce genetic variation.
Independent segregation: In meiosis 1, homologous pairs line up opposite each other at cell equator, it is random on which side of equator they lie. These pairs are separated so one of each HP ends up in the daughter cell. This creates a large number of possible combinations of chromosomes in the daughter cell, the amount can be calculated through 2^n
n=number of homologous pairs.
Crossing over: In meiosis 1, HP line up opposite each other at equator. Parts of chromatid can become twisted around each other causing chromatid to break from tension. The broken parts of chromatid recombine with another chromatid to create a new combination of alleles.
Random fertilisation: random egg and sperm fuse to increase variation.
How to identify meiosis in a life cycle?
Find a diploid (2n) parent cell dividing to become a haploid (n) cell.
Define mutation and describe a non disjunction mutation.
Mutation : change in the DNA base sequence.
Non-disjunction: When the chromsomes in meiosis 1 or 2 don’t separate equally in anaphase, this changes the number of chromosomes
Define polypoidy and aneuploidy
Polypoidy: Changes in whole sets of chromosomes
Aneuploidy: Changes in the number of individual chromosomes
Define substitution, deletion and insertion mutations.
Substitution: Base is replaced with another base (may not change amino acid as DNA i =s degenerative)
Deletion and Insertion: Base is removed or inserted into base sequence, this causes a frame-shift and is a more sever mutation.
