Intro to biochem

Question 1

Classes of nucleic acids found in cells

Answer 1

Ribonucleic - 90%

Deoxyribonhuycleic - 10%

Question 2

Classes of RNA

Answer 2

rRNA - 80%
tRNA - 15%
mRNA - 5%

Question 3

Functions of DNA

Answer 3

Repositiry of genetic info
Directs its own replication
Directs transcription of complimentary molecules of mRNA

Question 4

Function of mRNA

Answer 4

Carriers of genetic info

Directs translation of genetic info into proteins

Question 5

Function of tRNA

Answer 5

Translator of genetic info

Delivers AA during protein synthesis

Question 6

Function of rRNA

Answer 6

Components of ribosomes

Have structural and functional roles

Question 7

Purine bases

Answer 7

Adenine

Guanine

Question 8

Pyrimidine bases

Answer 8

Cytosine
Thymine
Uracil

Question 9

Nucleoside of adenine

Answer 9

Adenosine

Question 10

Nuceloside of guanine

Answer 10

Guanosine

Question 11

Nucleoside of cytosine

Answer 11

Cytidine

Question 12

Nucleoside of thymine

Answer 12

Thymidine

Question 13

Nucleoside of uracil

Answer 13

Uridine

Question 14

How to read nucleic acids

Answer 14

5’ to 3’

Question 15

Watson - Crick base pairing

Answer 15

A and T form 2 hydrogen bonds

G & C form 3 hydrogen bonds and are more stable

Question 16

Structure of B-DNA

Answer 16

Double stranded alpha-helix 
One full turn contains 10 base pairs 
Width of molecule is 2nm
Contains major and minor groove 
Distance between 2 base plates - 0.34 nm
Base pairs are orientated to the right angle of the helix

Question 17

DNA replication process

Answer 17

DNA Helicase separates parental strand into leading strand and lagging strand
DNA primase and RNA primers re used by DNA polymerase as starting points for replication
Leading strand (5’ to 3’) is replicated in a continuous fashion but the lagging strand is unable to - Okazaki fragnments
RNA primers are removed by exonuclease activity of DNA polymerase and are replaced w/ DNA
DNA Ligase seals fragments to complete synthesis of lagging strand

Question 18

Length of Okazaki fragments

Answer 18

1,000 to 5,000 bases

Question 19

Antiviral chemotherapeutic agents

Answer 19

Analogue nucleosides are phosphorylated at 5’ carbon –> triphosphate analogue. Reverse transcriptase then incorporates these into the viral genome and this blocks DNA synthesis –> no more chain elongation

Question 20

Why is DNA synthesis is blocked in antiviral chemotherapeutic agents

Answer 20

Analogues don’t have hydroxyl groups at 3’ and other atoms/ groups instead

Question 21

Structure of RNA molecules

Answer 21

Single stranded molecules
Nucleotides joined by phosphodiester bonds
Starts at 5’ end and terminates at 3’ end
Extensive 2’ structures e.g hairpin loop due to intramolecular double stranded regions

Question 22

RNA polymerases

Answer 22

Synthesis RNA 
Types are distinguished by the class of which they direct the synthesis

Question 23

RNA polymerase I

Answer 23

Direct the synthesis of rRNA’s

Question 24

RNA polymerase II

Answer 24

Direct synthesis of mRNAs

Sensitive to inhibition by alpha-amanitin, found in Amanita phalloides (mushroom)

Question 25

RNA polymerase III

Answer 25

Direct synthesis of tRNA

Question 26

Transcription - initiation

Answer 26

Interaction w/ RNA polymerase w/ spp sites on the DNA (promoters)

Question 27

Promoters

Answer 27

Charcteristic sequences of DNA in front of or upstream of the genes that is to be transcribed

Question 28

Transcription - elongation

Answer 28

RNA polymerase selects appropriate ribonucleotides and forms phosphodiester bridges between them Rapid process - 40 nt/ second Requires double stranded DNA to unwound

Question 29

How is double stranded DNA unwound in transcription

Answer 29

Topoisomerases I and II | These enzymes are associated w/ the transcription complex and are targets for anti-cancer drugs in chemo

Question 30

Transcription - termination

Answer 30

Diff types employ diff mechanisms to terminate transcription

Question 31

RNA polymerase I to terminate transcription

Answer 31

Uses spp protein

Question 32

RNA polymerase II to terminate transcription

Answer 32

Uses spp termination sequences & protein factors

Question 33

RNA polymerase III to terminate transcription

Answer 33

Uses spp termination sequences

Question 34

Features of prokaryotic mRNA's

Answer 34

Polycistronic No chemical modification No splicing

Question 35

Features of eukaryotic mRNA's

Answer 35

Monocistronic Chemical modifications Splicing - contains introns and axons

Question 36

Chemical modifications of eukaryotic mRNA

Answer 36

5': methylated guanine nucleotide cap added | 3': polyA tail added

Question 37

Monocistronic

Answer 37

Encode for only one protein

Question 38

Polycistronic

Answer 38

Encodes for multiple proteins

Question 39

When does transcription and translation occur in prokaryotes

Answer 39

Simultaneously -meaning that transcripts may already be partially transcribed into proteins even before transcription is completed

Question 40

Why can't simultaneous transcription and translation occur in eukaryotes

Answer 40

Nuclear envelope acts as a barrier between process of transcription and translation

Question 41

Structure of tRNA

Answer 41

``` Acceptor stem T Psi C loop Variable loop Anticodon loop Trinucleotide anticodon D loop ```

Question 42

Acceptor stem

Answer 42

Last 3 bases unpaired and form acceptor stem | AA is joined to 3' end by an ester bond between hydroxy group on adenosine nucleotide and carboxyl group on AA

Question 43

Trinucleotide anticodon

Answer 43

Trinucleotide codon directs a spp interaction w/ the corresponding don in the mRNA

Question 44

Secondary structure of tRNA

Answer 44

Cloverleaf

Question 45

Ribosome-inhibiting antibiotics

Answer 45

As ribosomes in prokaryotes and eukaryotes are different compounds can preferentially target bacteria ribosome

Question 46

Antibiotics targeting 30S subunit

Answer 46

Streptomycin | Tetracycline

Question 47

Antibiotics targeting 50S subunits

Answer 47

Erythromycin | Chloramphenol

Question 48

Nucleotide triphosphates

Answer 48

Substrates for nucleic acid synthesis

Question 49

When is PPi released

Answer 49

During the incorporation of nucleotide triphosphates into the nascent acid chain

Question 50

PPi

Answer 50

Pyrophosphate

Question 51

Tertiary structure of DNA

Answer 51

Chromatin and nucleosomes DNA is wrapped around histones found in core of nucleosomes, found in chromatin Each nucleosome has a pice of linker DNA in between which allows extra folding of nucleosome string --> supercoiled structure