DNA and genome Flashcards
(15 cards)
Prokaryotes
Bacteria are prokaryotes. They do not have a membrane-bound nucleus and their DNA is free in the
cytoplasm
.
Bacteria have a single circular chromosome in the centre of the cell that holds all the genes needed for that bacterium. Bacteria also have extra circles of DNA called plasmids.
These plasmids contain additional genes, such as for antibiotic resistance, which may increase a bacterium’s chance of survival.
Eukaryotes
Animals, plants and fungi are eukaryotes. They have a membrane-bound nucleus and their chromosomes are linear rather than circular.
The DNA found in the linear chromosomes within the nucleus is tightly coiled and packaged around special proteins called histones - as shown below.
Interestingly, circular chromosomes are also found in
mitochondria
and chloroplasts. They both use their own DNA to make some proteins needed for their function. This gives evidence for the theory that mitochondria and chloroplasts originated from prokaryotic cells that were engulfed by a larger cell.
requirements for DNA replication
- original DNA template
- free DNA nucleotides
- DNA polymerase
- primers
Stages of DNA replication
- DNA unwound and unzipped special molecules break weak hydrogen bonds between bases
- DNA polymerase will add the free DNA nucleotides using complementary base pairing (A-T and C-G) 3’ to 5’
Leading strand is synthesised continuously. DNA polymerase adds nucleotides to the deoxyribose (3’) ended strand in a 5’ to 3’ direction.
Lagging strand is synthesised in fragments. Nucleotides cannot be added to the phosphate (5’) end because DNA polymerase can only add DNA nucleotides in a 5’ to 3’ direction. The lagging strand is therefore synthesised in fragments. The fragments are then sealed together by an enzyme called ligase. - The two new strands twist to form a double helix. Each is identical to the original strand.
definition of phenotype
The visible characteristics of an organism which occur as a result of its genes.
what does missense do
causes shape change in protein which ma or my not affect its function
what does nonsense mutation do
causes an early stop codon resulting in shorter protein
what does splice site do
may prevent splicing in site, introns may be included or exons excluded
what is a point mutation
substitution mutation
substitution mutations
missense nonsense splicesite
frameshift mutations
insertion and deletion
frameshift mutations usually result in..
non functional protein. significantly different from point of mutation
duplication is
duplication occurs when a section of a chromosome is added from its homologous partner.
inversion is
inversion is where a section of a chromosome is reversed.
