central dogma of bio

Question 1

outline the central dogma

Answer 1

genetic info flows from
DNA –(transcription)–> RNA
–>(translation)–> proteins

Question 2

where does DNA synthesis take place?

Answer 2

inside the nucleus of the cell

Question 3

where does DNA transcription take place?

Answer 3

inside the nucleus of the cell (same as DNA synth)

Question 4

structural features of cell nucleus

Answer 4

outer/inner nuclear membrane = nuclear envelope
outer continuous w ER
nuclear pores
DNA and proteins inside
nucleolus

Question 5

describe the nucleolus and its purpose

Answer 5

25% of volume of nucleus, made of proteins and RNA
Site of ribosome synthesis:
transcribes ribosomal RNA (rRNA) and combines it with proteins to form ribosomes

Question 6

describe DNA replication briefly

Answer 6

DNA strands unzipped
each strand acts as a template to form two complementary strands –> two identical daughter DNA double helices

Question 7

DNA synthesis is catalysed by

Answer 7

DNA polymerase

Question 8

how does DNA polymerase catalyse DNA synthesis

Answer 8

catalyses the stepwise addition of a base to the 3’ end of a chain
editing function - proofreads at the same time as polymerisation
nuclease clips off wrong nucleotide

Question 9

DNA synthesis occurs in which direction

Answer 9

5’ –> 3’
bases added to 3’ end

Question 10

what is the DNA daughter strand / lagging strand?

Answer 10

DNA synthesised only 5’-3’
daughter strand = continuously synthesised, leading
lagging strand = discontinuous Okazaki fragments, stitched together

Question 11

role of DNA ligase

Answer 11

an enzyme that joins DNA strands together by catalysing the formation of a phosphodiester bond
joins Okazaki fragments

Question 12

what is error prone replication

Answer 12

a strategy commonly used by viruses where nucleotides are synthesised without fidelity to mutate + evolve to avoid the host
common in RNA viruses

Question 13

how can cells regulate the expression of each of its genes

Answer 13

by controlling the production of its RNA, and hence the amount of protein produced after translation

Question 14

what is transcription

Answer 14

DNA –> single stranded complimentary RNA

Question 15

DNA is transcribed by what enzyme?

Answer 15

RNA polymerase
(eukaryotic cells have three types, bacteria have 1)

Question 16

how does RNA polymerase work

Answer 16

moves stepwise along DNA, unwinding a small portion just ahead of the active site for polymerisation
RNA chain extended in 5’-3’ direction
fast process, modest proofreading system

Question 17

how is transcription initiation carried out

Answer 17

by RNA polymerase II
requires transcriptional activator proteins which bind to specific short sequences of DNA (eg. TATA box)

Question 18

after the primary RNA transcript is produced what happens
(eukaryotic cells)

Answer 18

5’ capping
RNA splicing (removing introns)
3’ polyadenylation
–> produces resulting mRNA, matures as it is transported from nucleus to cytoplasm via nuclear pore complex

Question 19

how is splicing of primary RNA transcript signalled and executed?

Answer 19

signalled by nucleotide sequences
a specific adenine nucleotide in the intron attacks the 5’ splice site, cutting backbone, covalently links, creating loop
3’ OH end of exon reacts w start of next exon, releasing intron sequence

Question 20

describe alternative splicing and give an example of where it occurs

Answer 20

not always the same exons
–> generates a variety of transcripts from the same gene
eg. antibody reproduction

Question 21

explain the main difference between bacterial and eukaryotic mRNAs

Answer 21

polycistronic - bacterial mRNAs contain instructions for several different proteins (ie, multiple sequence segments in one mRNA)
bacterial mRNAs 5’ and 3’ ends are unmodified

Question 22

after transcription, where is mRNA located

Answer 22

in the cytoplasm, adjacent to the ER

Question 23

mRNA function

Answer 23

messenger RNA
the final product of transcription
template for protein synthesis during TRANSLATION

Question 24

tRNA function

Answer 24

transfer RNA
brings amino acids + reads genetic info during translation

Question 25

rRNA

Answer 25

ribosomal RNA
along with proteins makes up ribosomes
catalyses translations

Question 26

where are eukaryotic ribosomes assembled

Answer 26

in the nucleolus, where they associate with rRNAs
then exported to cytoplasm, coats ER

Question 27

general structure of a ribosome

Answer 27

large and small subunits
A, P, E sites (amino acyl, peptidyl RNA and exit)
binding site for mRNA

Question 28

how to ribosomes translate mRNA into proteins

Answer 28

two subunits join around mRNA 5’ end
mRNA pulled through, codons translated into amino acid sequence using tRNA to add each amino acid

Question 29

structure of tRNA

Answer 29

a four leaf clover structure
one end is the anticodon, three consecutive nucleotides that pair w the complementary codon in an mRNA
the other end has single stranded 3’ region, attaches to matching amino acid
two loops to either side

Question 30

role of tRNA synthetases

Answer 30

editing and proofreading to select the correct amino acid (highest affinity to active site) to attach to the 3’ end of the tRNA

Question 31

after proteins are produced from translation and folded, how do they know where to go?

Answer 31

signal sequences
15-60 amino acids long, often removed from the finished portion once delivered

Question 32

what is recombinant DNA technology

Answer 32

isolate + manipulate DNA segments of interest
can combine DNA of different species and produce new genes

circular double stranded plasmid DNA (cloning vector) cleaved with nuclease, DNA fragment to be cloned is ligated with DNA ligase
cell reproduces with the protein of interest.

Question 33

what is the polymerase chain reaction

Answer 33

a simple way to selectively amplify specific DNA fragments with heat
Primer strands –> DNA synth catalysed by Taq polymerase (purified from thermophilic bacterium)
each cycle doubles amount of DNA

Question 34

DNA sequencing methods

Answer 34

old method: four different chain terminating bases produces different sets of products, separated by electrophoresis. read bands.

Illumina dye sequencing: distinguishes base by size/ charge using reversible dye-terminators

Question 35

producing cDNA

Answer 35

copyDNA, contains introns and exons
mature mRNA –> reverse transcriptase (viral) –> copies
back-produce double stranded cDNA