Lecture Eleven - Molecular genetics (DNA) Flashcards
What is genetics?
The study of inherited variation due to genes.
What are the three broad fields of genetics?
Transmission (or classical) genetics - How traits (phenotypes or characteristics) are passed from parent to offspring.
Molecular genetics - How the hereditary material (DNA) controls the expression of genes and thus traits.
Evolutionary and population genetics - Genetic variation and its role in evolution.
What are the four levels that genetics can be look at?
The molecular level (alleles), cellular level (pigment levels in cells), organismal level (phenotypes) and the population level (depends on environmental conditions).
How was is shown that DNA is the genetic material (as opposed to proteins)?
Chromosomes contain DNA and proteins.
Hershey-Chase - Used bacteriophages (virus that infects bacteria). The knew that the genetic materials of the phage must enter the bacteria and take over machinery of bacterial cell.
The looked to see whether the DNA or protein was being inserted into the bacteria by radioactively marking proteins in one condition and DNA in another.
The bacterial cells and free viruses were then separated in a blender. Solution was then centrifuged, and it was then looked at to see which part of the solution contained radioactive substances.
Differentiate between purines and pyrimidines.
Purines = two rings.
Pyrimidines = one ring.
A and T form two bonds.
C and G form three bonds.
What is the chemical structure of DNA.
Sugar phosphate backbone.
Sugar molecule is covalently bonded to phosphate molecule, this is called a phosphodiester bond.
Sugar then covalently bonds to one of the four bases.
One end of the DNA strand ends with a phosphate group = 5’.
One end of the DNA strand ends with a sugar = 3’.
How is DNA copied? (Conservative/semi-conservative or dispersive replication?)
Semi-conservative.
One double helix is split, then in the two new strands of DNA, one strand is form the original strand, and one strand is new.
What is a gene?
Sequence of DNA that can code for a protein.
Not all sequences of DNA code for genes.
Not all genes code for proteins.
How are genes expressed?
DNA - transcription -> mRNA - translation -> Polypeptide
Transcription:
DNA is copied into messenger (mRNA) RNA in the nucleus.
In mRNA, there is U instead of T.
RNA is processed (removal of introns (splicing)). This involves pre-mRNA becoming mature mRNA.
Translation:
In the cytoplasm, on ribosomes, codons (triplet codes of bases) are joined together, using the mRNA template.
What is a genome?
Entire DNA sequence of an organism.
The human genome is made up of ~1.5% coding sequences.
The rest is non-coding sequences of DNA.
~24% is gene-related, introns and regularly regions.
~75% is other non-coding DNA.
What are DNA mutations?
All genes mutate spontaneously and randomly. Different levels of mutation: Point mutations. Chromosomal mutations. Changes in chromosome numbers.
Silent mutations = point mutations of a single base, that causes the same amino acid to be coded for, thus no change in the protein produced.
Missense mutations = Change in base, which leads to a change in the amino acid coded for, and therefore a change in the protein produced (if in an exon coding region).
Nonsense mutation = Change in base which causes the amino acid coded for to be a stop codon, thus changing the length of the polypeptide, thus changing the entire protein.
What is the theory of central dogma?
DNA -> RNA -> Protein
