A1 eukaryotic gene expression and function Flashcards by lily stratton

where is DNA copied into

RNA in the nucleus

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where is processed RNA exported to

cytosol

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where does translation take place

cytosol

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what is the 5’ end of DNA usually attached to

phosphoryl group

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what is usually at the 3’ end of DNA

free hydroxyl group (OH)

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what bases are purines

adenine and guanine

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what bases are pyrimidines

cytosine and thymine

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the 4 DNA bases

adenine, guanine, cytosine, and thymine

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the 4 RNA bases

adenine, guanine, cytosine, and uracil

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what is a nucleoside

a base (A, T, G, C) conjugated to a sugar

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nucleoside bases (DNA)

deoxyadenosine
deoxyguanosine
deoxycytosine
thymidine

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nucleoside bases (RNA)

adenosine
guanosine
cytidine
uridine

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what is a nucleotide

a nucleoside conjugated to one or more phosphoryl group

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nucleotide bases in DNA

deoxyadenylate (dATP)
deoxyguanylate (dGTP)
deoxycytidylate (dCTP)
thymidylate (dTTP)

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what sugar is DNA and RNA based on

RNA- ribose
DNA- deoxyribose

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what bond holds bases together

hydrogen bonds

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structure of DNA

2 polynucleotide chains coiled round common axis with a right handed screw
chains are anti-parallel
double helix

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location of sugar phosphates and bases on DNA helix

sugar phosphates on outside
bases on inside

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what degree are bases at to helix axis

90 degrees

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how do the stacked bases at the core of the double helix attract each other

van der waals forces

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is the double stranded DNA stable or unstable

very stable

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why does DNA replication need to be error free

to avoid mutation

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what are the stages of the cell cycle

G1 growth
S dna synthesis
G2 growth and prep for mitosis
M- mitosis (cell div)

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at what phase in the cell cycle does DNA replication take place

S phase

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why is DNA replication said to be semi conservative

because one complete strand of each double helix is directly derived from the parent molecule and one complete new strand

what is the key enzyme involved in DNA replication

DNA polymerase

what does DNA pol require to begin synthesis

primer (with a free 3'-OH)

what does DNA pol do in DNA replication

catalyses step by step addition of deoxyribonucleotide units too DNA

what is the new DNA assembled onto

template DNA

in what direction does new DNA grow at

3' end

what direction is DNA synthesis

5'-3'

what are the 2 strands in DNA replication called

leading and lagging strand

explain the lagging strand

short sequences of DNA are synthesised (okazaki fragments)

what enzyme joins okazaki fragments

DNA ligase

what are introns

intervening DNA non coding regions

what are exons

expressed DNA coding regions

what are the 3 main types of RNA

messsenger RNA (mRNA) transfer RNA (tRNA) ribosomal RNA (rRNA)

what is mRNA

template for synthesis of proteins

what is mRNA transcribed by

RNA polymerase II

what is tRNA

carries activated amino acids to ribosomes

what is tRNA synthesised by

RNA polymerase III

what is rRNA

major component of ribosomes

what is rRNA synthesised by

RNA polymerase I

what do the 3 main types of RNA require to copy template DNA

ATP UTP CTP GTP together with Mg2+ ions

what are the three steps of mRNA synthesis

1. Initiation 2. Elongation 3. Termination

summary of initiation in mRNA synthesis

RNA Pol II and transcription factors assemble at promoter sites ; RNA synthesis then initiates

summary of elongation in mRNA synthesis

-RNA pol moves along DNA template to synthesis mRNA which grows in a 5'-3' direction -Sequence of growing mRNA driven by base pairing to DNA strand- faithful copy of DNA template produced

summary of termination in mRNA synthesis

RNA pol II ceases transcription at defined site mRNA transcript is then stabilised by specific modifications

what are the two promotor boxes

CAAT box (sometimes present) TATAAA box (Hogness box)

what strands can the CAAT and TATA box be on

CAAT can be on either TATA can only be on one

transcription goes from

DNA to RNA

translation goes from

RNA to protein

are mRNA and DNA complementary

yes

what are the names of the coding and template strand

coding - sense template -antisense

approximately how many base pairs of DNA are unwinded

what direction is DNA strand read in during elongation

3'-5'

what protective features are added to the transcript

cap at 5' long poly (A) tail at 3'

can transcription factors turn gene expression on or off

yes

are transcription factors specific

yes

what are transcription factors activated by

by phosphorylation and subsequent movement into the nucleus

what is used as a template for protein synthesis

mRNA

what is the role of tRNAs in protein synthesis

translate the genetic code and allow specific amino acids to be added to a growing protein chain

where does translation occur

on ribosomes

what is essential for protein synthesis and how are they delivered to the ribosome

amino acids delivered to ribosome on tRNAs (aminoacyl-tRNA)

what is the start codon for protein synthesis

AUG (methionine)

what structure is adopted by tRNAs and how

clover leaf structure H bonding between bases

where is the anticodon located on the clover leaf structure of tRNA

at the base will then base pair with corresponding condon in mRNA being translated ensuring specificity

amino acids are attached as what and where on tRNA

attached as an aminoacyl moiety and the amino acid attachment site

what do aminoacyl tRNA synthetases do

link a specific amino acid with a specific tRNA (defined by its anticodon)

what are the 3 steps for linking aa to specific tRNa with chem eqn

amino acid activation step transfer of aminoacyl-AMP to specific tRNA driven by hydrolysis of pyrophosphate (PPi) aa+ATP --- aminoacyl-AMP + PPi aminoacyl-AMP + tRNA --- aminoacyl-tRNA +AMP PPi + water --- 2Pi

overall equation of the 3 step process to link aa to tRNA

amino acid + ATP + tRNA + H2O --- Aminoacyl-tRNA + AMP + 2Pi

how many aminoacyl-tRNA synthetases are there per amino acid

one

how do synthetases reject the incorrect amino acid

they have a proof reading ability can recognise the tRNA structure and its anticodon allowing specificity

what are ribosomes made up of

50S and 30S rRNA subunits

what are the 3 sites on ribosomes (P, A, E)

P- peptide grows here through a tunnel in the structure A- amino acyl-tRNA binds here, bringing in next amino acid E- exit site for empty tRNA

what is Met-tRNAi

special intiation tRNA bearing methionine key for translation initiation

what two things (with initiation factors) form a complex in translation initiation

GTP and 30S ribosomal subunit

what does the complex scan mRNA for and what is the energy source in translation initiation

looking for AUG (initiation codon) uses ATP

what occurs when complex finds AUG in translation initiation

once AUG is found, the remaining ribosomal subunit (50S) is recruited with further initiation factors to form the 80S initiation complex, allowing protein synthesis to begin

what are some of the many regulatory steps of protein synthesis

selective control of gene expression control of mRNA synthesis rates protein synthesis/degradtion rates