Biochemistry: From DNA to Protein

Question 1

genome

Answer 1

all the DNA in each cell

Question 2

nucleoside

Answer 2

base and sugar

Question 3

nucleotide

Answer 3

nucleoside and phosphate

Question 4

where do phosphodiester bonds occur

Answer 4

between the free 3’ OH and 5’ triphosphate of two nucleotides

Question 5

how do nucelotide analogues work as drugs

Answer 5

have a higher affinity for viral DNA than human and stop elongation as they lack a 3’ OH

Question 6

role of DNA helicase

Answer 6

unwinds DNA strand

Question 7

what synthesised RNA primers

Answer 7

primase

Question 8

describe the leading strand

Answer 8

DNA replicated 5’ to 3’ in one continuous strand

Question 9

describe the lagging strand

Answer 9

DNA replicated 5’ to 3’ in short okazaki fragments which are later bound together

Question 10

describe DNA polymerases role in proof reading

Answer 10

exonuclease activity - remove incorrect nucleotides

Question 11

what are stem loops

Answer 11

regions of intra-molecular base pairing in DNA

Question 12

what are the 3 classes of RNA

Answer 12

• mRNA
• tRNA
• rRNA

Question 13

what types of RNA are stable

Answer 13

tRNA and rRNA

Question 14

describe mRNA

Answer 14

carries genetic information for protein synthesis

Question 15

describe tRNA

Answer 15

carries amino acid to be incorporated into protein

Question 16

describe rRNA

Answer 16

bnds with proteins to form ribosomes - site of protein synthesis

Question 17

what is the 2D shape of tRNA

Answer 17

clover leaf

Question 18

anti-codon

Answer 18

triplet of bases that are complementary to a codon on the strand being replicated

Question 19

what are the 3 eukaryote RNA polymerases

Answer 19

Pol I, Pol II, Pol III

Question 20

what RNA polymerase synthesises all mRNA

Answer 20

Pol II

Question 21

give a brief overview of transcription

Answer 21

• TATA box at -25 makes a kink in the DNA determining transcription start point and direction
• general transcription factors are needed for initiation
• transcription bubble moves along the DNA being unwound infrontof the polymerase and rewound behind it
• new RNA strand creates a stem loop and a sequence of U bases to terminate transcription, mRNA is cleaved and DNA polymerase dissociates

Question 22

how is transcription regulated

Answer 22

by transcription factors binding to enhancers

Question 23

what are the 2 domains of transcription factors

Answer 23

• DNA binding region

- transcription activated region

Question 24

describe how steroid receptors regulate transcription

Answer 24

• steroid is activated and translocates to the nucleus where it binds to SREs on DNA and regulates transcription either -ve or +ve

Question 25

describe how glucocorticoid receptors regulate transcription

Answer 25

• bound to albumin/transporter protein in blood and enter the cell via diffusion once free
• binds to inactive steroid receptor in the cytoplasm and translocates to nucleus
• binds to SRE

Question 26

what is at the ends of mRNA

Answer 26

• 3’ - poly(A) tail

- 5’ - G cap

Question 27

give a brief overview of translation

Answer 27

• initiation factors initiate (using GTP)
• small ribosomal subunit binds to the 5’ end of mRNA and looks for a start codon
• once found the initiator tRNA pairs at the P site and the large ribosomal subunit joins
• elongation factors bring the next tRNA which binds at the A site, GTP hydrolysed, EF released
• peptide bonds form between the P and A site - peptide in A
• the free tRNA moves to the E site and exits (reused later)
• the peptide is now in P and the A site is free for the next tRNA
• once a stop codon is reached there is no tRNA pairinf and a release factor bonds in its place
• GTP hydrolysed, protein cleaved and tRNA, mRNA and rRNA dissociate

Question 28

how is the genetic code degenerate

Answer 28

many amino acids have more than 1 codon

Question 29

how is the genetic code unambiguous

Answer 29

codons code for 1 amino acid or a stop

Question 30

function of amino-acyl tRNA synthases

Answer 30

binds amino acid to its corresponding tRNA (needs ATP)

Question 31

what catalyses peptide bond formation

Answer 31

peptidyl transferase

Question 32

what 3 things can happen after protein synthesis

Answer 32

• modification
• targeting
• degradation

Question 33

modification

Answer 33

addition of chemical groups to proetin

Question 34

targeting

Answer 34

protein moved to final cellular destination

Question 35

degradation

Answer 35

unwanted/damaged proteins removed

Question 36

‘free’ ribosomes

• are located where
• make proteins for where
• proteins are moved when

Answer 36

• in cytosol
• cytosol, nucleus, mitochondria
• post-translationally

Question 37

‘bound’ ribosomes

• are located where
• make proteins for where
• proteins are moved when

Answer 37

• bound in rough ER
• ER, golgi, secretions, plasma membrane
• co-translationally

Question 38

types of post-translational modifications

Answer 38

• glycolysation - addition of carbs in ER/golgi
• formation of disulphide bridges
• folding and assembly of multisubunits in ER
• cleavage in ER, golgi or vesicles

Question 39

what is I-cell disease

Answer 39

inherited recessive disorder of protein targeting

- lysosomes are sorted right in the golgi and are secreted but unable to digest stuff

Question 40

what is a consequence of I-cell disease

Answer 40

early death