DNA Flashcards
features of a genetic code
6
each aa in protein is coded for by 1 codon on mRNA
some aa only have 1 codon
degenerate code
3 stop codons
non overlapping
universal
degenerate
most aa have more than 1 codon
RNA structure
pentose sugar ribose
organic bases a g c u
phosphate group
how is mRNA structure suited to its function
has correct triplet sequence of organic bases that code for specific pp
easily broken down only exists while needed to manufacture a given protein
transcription
process of making pre mRNA using part of the dna to act as a template
what is a codon
sequence of 3 bases triplet on mRNA that codes for a single amino acid
How proto- oncogenes stimulate cell division
growth factors attach receptor protein cell surface membrane via relay proteins cytoplasm “switch on” genes needed for DNA replication
Two ways oncogenes affect cell division
1) receptor protein cell surface membrane PERMANENTLY ACTIVATED - cell div switched on even absence of growth factors
2) CODE FOR GROWTH FACTOR-produced in excessive amounts, stimulating excessive cell division
mutated tumour suppressor gene
becomes inactivated, stops inhibiting cell division -> increases
proteins made by tumour suppressor genes may
REPAIR damaged DNA before replication
control cell adhesion + keep cells in their place
INHIBIT cell division
How genes are prevented from expressing themselves
PREVENTING TRANSCRIPTION-preventing production MRNA
BREAKING DOWN MRNA bef its genetic code can be translated
Stem cells
Undifferentiated dividing cells that occur in adult mammal tissues and need to be constantly replaced
Palindromic Recognition sites
Reads same both ways E.g GGATCC same as CCTAGG in opposite direction
5 main stages of genetic fingerprinting
Extraction Digestion Separation Hybridisation Development
1st stage of genetic fingerprinting
Extraction
extract DNA from rest of the cell
2nd stage of genetic fingerprinting
Digestion
DNA cut into fragments by REN
endonuclease chosen for ability to cut close to but not within groups of core sequences
3rd stage of genetic fingerprinting
separation
fragments sep according size by gel electrophoresis under influence of electrical voltage
gel immersed in alkali sep double strands into single strands
single stands transferred onto nylon membrane via SOUTHERN BLOTTING TECHNIQUE
5th stage of genetic fingerprinting
Development
x ray film put over nylon membrane- film exposed by radiation from radioactive probes
(if use fluorescent probes positions are located visually)
these points correspond to the position of the DNA fragments separated during electrophoresis, series of bars revealed - unique every human
Southern blotting technique
thin nylon membrane laid over the gel
membrane covered in several sheets absorbent paper- draws up liquid containing DNA by capillary action
this transfers the DNA fragments to nylon membrane in same relative positions they occupied on the gel
DNA fragments fixed to membrane using U.V light
why is the gel used in electrophoresis for a genetic fingerprint immersed in alkali
to separate the double stands into single stands
4th stage of genetic fingerprinting
Hybridisation
radioactive/fluorescent probe used to bind with core sequences. Probes have complementary base sequences to core sequence- bind under specific conditions- temp/PH
process carried out different probes each of which binds with a diff core sequence
In PCR what are primers
Short pieces of DNA that have a set of bases complementary to those at the end of the DNA fragment to be copied
Why are two different primers required
The sequences at the opposite ends of the two DNA stands are different
