DNA quick flashcards

what is transformation

change in genotype and phenotype due to assimilation of external DNA by a cell

F.Griffith worked with Streptococcus pneumoniae to discover transformation, using mice

what are bacteriophages

viruses that infect bacteria

what is chargaff’s rule

A=T

G=C

how does DNA replicate

separation of two DNA strands & serve as a template

complentary base pairs join to each template

nucleotides connected, each daughter DNA molecule has one parental and one new strand

what is the semiconservative model

two strands of the parental molecule separate

each function as a template for a new complementary strand

what is the origin of replication

site where proteins attach and separate the strands of DNA

what is DNA polymerase

enzyme that adds new nucleotides to the replication fork at rate of 50 to 500/s

what is nucleoside triphosphate

energy and substrate for polymerisation

what end do nucleotides get added to

3’ end

what is the leading strand

replicated towards replication fork continuously

what is the lagging strand

replicated away from replication fork in okazaki fragments

what are okazaki fragments

100-200 nucleotide pieces that are joined by DNA ligase into a single strand

what is a primer

start of new DNA chain which is bade of RNA

about 10 base pairs long

needed to initiate replication

what is primase

enzyme that joins RNA nucleotides into a primer

can initiate the process from scratch

what are helicases

enzyme that untwists and separates the DNA helix

what are single strand binding proteins

binds to seprated strands and holds them apart

what is mismatch repair

incorrectly paired nucleotides are fixed by an enzyme

what is nuclease

enzyme that cuts DNA

what is nucleotide excision repair

excised DNA section filled in by a polymerase and ligase

nuclease cuts damaged DNA strand, DNA polymerase fills gap, DNA ligase seals the remaining nick

how can prokaryotes avoid the 5’ problem

they have circular DNA

what are telomeres

repeated short sequences of DNA added to the end of chromosomes for protection against loss of genetic material

TTAGGG in humans

what is telomerase

enzyme containing RNA which further lengthens the 3’ end to allow completion of the 5’ end

generally only in germ cells

one gene one enzyme hypothesis - beadle and tatum

Neurospora crassa grows with agar, salts, glucose and biotin

used x rays to induce mutations (strains that can’t grow with just those nutrients)

used supplemented agar treatments to see which amino acids/nutrients required for growth

what is mRNA

carries building instructions from a gene

mRNA in eukaryotes vs prokaryotes

Prokaryotes - MRNA transcribe directly from DNA, immediately translated into a polypeptide

Eukaryotes - the transcribed RNA is further processed to form mRNA

what is a codon

the mRNA triplet code for an amino acid

what direction are codons read

5’ to 3’

what is RNA polymerase

pries apart DNA helix and hooks together the RNA nucleotides

can only add nucleotides to 3’ end

what is a promoter

region of DNA where RNA polymerases attaches and initiates transcription

what is the transcription unit

the stretch of DNA that’s transcribed

what is the terminator

the DNA sequences that signal the end of transcription

what is the 5’ cap

modified guanine nucleotide

protects mRNA from hydrolytic enzymes

helps attach mRNA to ribosome

what is the Poly(A) tail

50-250 adenine nucleotides

inhibits degradation

helps ribosomes attach

helps mRNA leave nucleus

what are ribozymes

RNA that act as enzymes

what are snRNPs

small nuclear ribonucleoproteins

found in nucleus

leads to spliceosome formation and catalyse the excision of introns

what is the spliceosome

several snRNPs and proteins which splice the exons into mRNA

almost as big as the ribosome

why are introns present

some introns control the activity of specific genes once excised

allows alternative RNA splicing, where different sections are excised from pre-RNA to code for different proteins

what are exons

sections of DNA and RNA that become expressed or translated into protein

transcribed into preRNA

what are introns

intervening, non expressed regions of RNA and DNA

transcribed into preRNA

what is tRNA

moves amino acids from cytoplasm into ribosome

specific to one or several codons and coded as an anti-codon

eg mRNA: CGU → tRNA: GCA

what is Aminoacyl-tRNA synthetase

20 forms

each one specific to one amino acid

attaches the amino acid to an appropriate tRNA

what is an activated amino acid

tRNA with an appropriate amino acid attached

what is the ribosome

acts to couple tRNA and mRNA

composed of rRNA and proteins

3 binding sites for tRNA

what is the A site of the ribosome

attaches to next tRNA

what is the P site of the ribosome

holds tRNA iwth growing polypeptide chain

what is the E site of the ribosome

releases tRNA

what are initiating factors

proteins which attach large RS to complex

initiator tRNA in P site

how to initiate a polypeptide

small RS binds to mRNA at 5’ cap and a initiator tRNA

GTP is energy source

what is the release factor

protein which binds directly to stop codon in A site

hydrolyses the polypeptide and releases it

triggers ribosome complex to disassemble

what are polyribosomes

multiple ribosomes translating the same mRNA

makes many copies of a protein quickly

what is a signal peptide

about 20 amino acids near leading end of a polypeptide

indicate the destination of the protein

what is the SRP

protein-RNA complex that recognises signal peptides and facilitates their movement to target locations

only in eukaryotes

protein synthesis in prokaryotes vs eukaryotes

prokaryotes - transcription & translation of the same mRNA can occur simultaneously

eukaryotes - nucleus prevents simultaneous transcription & translation, allows for extra regulation of cell’s activity

point mutations

changes in one base pair of a gene

if in gametes, can pass to offspring

what is substitution

replacement of one base pair with another

what are silent mutations

have no effect on the protein

what are missense mutations

changes one amino acid which can alter the protein and its function

what are nonsense mutations

introduces a premature stop codon

often leads to non functional proteins

what are insertions/deletions

adding/losing a base pair in a gene

generally leads to a frameshift mutation, where insertion/deletion isn’t a multiple of three so amino acids are added incorrectly