S&F; Gene to Protein

Question 1

what is the definition of gene expression?

Answer 1

the process of going from dna to a functional product

Question 2

genotype

Answer 2

an organisms hereditary information

Question 3

phenotype

Answer 3

actual observable or physiological traits

Question 4

what are the three main steps to gene expression?

Answer 4

transcription of rna from dna
processing pre mrna transcript
translation of mrna transcript to protein

Question 5

three steps to transcription

Answer 5

initiation; polymerase binds to promoter
elongation; moves downstream through the gene transcribing rna
termination; detaches after terminator reached

Question 6

why does dna have to be stable?

Answer 6

dna has to last because it holds everything as a blueprint

Question 7

transcription; initiation

Answer 7

the assembly of multiple proteins
several transcription factors bind to the dna (an eukaryotic promoter)
the transcription initiation complex forms

Question 8

transcription; elongation

Answer 8

elongation; complementary rna nucleotides added to 3’ end of growing transcript.. double helix reforms as transcript leaves the template strand

Question 9

transcription; termination

Answer 9

after transcription of the polyadenylation signal, nuclear enzymes release pre-mrna and rna polymerase, then dissociates from dna

Question 10

what are the processes of the mRNA

Answer 10

capping, tailing and splicing

Question 11

what is capping?

Answer 11

when a modified guanine nucleotide is added to the 5’ end

Question 12

what is tailing?

Answer 12

when 50-250 adenine nucleotides (polyA) are added to the 3’ end

Question 13

benefits of capping + tailing

Answer 13

they are thought to facilitate export, confer stability and facilitate ribosome binding in cytoplasm

Question 14

what is splicing?

Answer 14

introns are removed from the transcript and exons are rejoined to form mature mrna

Question 15

what are exons?

Answer 15

coding regions (inc UTRs)

Question 16

what are introns?

Answer 16

non-coding regions intervening exons

Question 17

UTR

Answer 17

untranslated regions at 5’ and 3’ ends

Question 18

where does splicing occur?

Answer 18

at the spliceosome (within the nucleus)
a large complex of proteins and small rnas.

Question 19

what is alternatice splicing

Answer 19

a process by which different combinations of exons are joined together. resulting in production of multiple forms of mrna from a single premrna.

Question 20

what are the three steps to translation

Answer 20

initiation, elongation, termination

Question 21

where is the binding site for mrna/trna

Answer 21

ribosome;
has a site (holds next in line trna)
p site; holds trna carrying the growing polypeptide
e site; trnas exit from here

Question 22

translation; initiation

Answer 22

1. small ribosomal subunit w initiator trna already bound bind 5’ cap of mrna
2. srs scans downstream to find translation start site (aug)
3. hydrogen bonds form bt initiator anticodon + mrna
4. large ribosomal subunit binds -> completing the initiation complex

**gtp is required.

Question 23

translation; elongation 3 steps

Answer 23

codon recognition, peptide bond formation, translocation

Question 24

codon recognition

Answer 24

base pairs with complementary anticodon
gtp invested to increase accuracy/efficiency

Question 25

peptide bond formation

Answer 25

large subunit rrna catalyses peptide bond formation + removes it from tnra in p site

Question 26

translocation

Answer 26

moves trna from a to p site. trna in p site moves to e and is released. gtp required.

Question 27

what happens to the trna after exiting e site?

Answer 27

they are reloaded back into the cytplasm by aminoacyl-trna enzymes.

Question 28

translation;termination +explanation

Answer 28

1. ribosome reaches a stop codon on mra (uag,uaa,uga)
2. release factor promotes hydrolysis, polypeptide si released
3. ribosomal subunits and other components dissociate; hydrolysis of 2 gtp molecules required

–> ribosome components can be recycled.

Question 29

how is gene expression tightly regulated

Answer 29

there are multiple control points!
1. transcription factors need to assemble and dna needs to be accessible.
2. capping, extent of polyadenylation, alternate splicing, producing an mrna able to be translated.
3. specific proteins assist in nuclear export of mrna
4. regulatory proteins can block translation, variable mrna life spans

Question 30

why is control of genes important?

Answer 30

to achieve the right thing at the right time in the right place!

Question 31

what is a housekeeping protein?

Answer 31

proteins that are being continuously produced
protein and mrna are present in larger quantities.
typically have longer half life

Question 32

what are the proteins that aren’t housekeepers?

Answer 32

they produce in response to stimuli

Question 33

what is the primary structure of an amino acid.

Answer 33

amino group and carboxyl group and side chain.

Question 34

polypeptide chain primary structure

Answer 34

held by covalent bonds between amino acids

Question 35

does dna go from 5’ to 3’ or the other way

Answer 35

5’ to 3’

Question 36

which cn connects to 35

Answer 36

n = 5
c = 3

Question 37

what are the other types of structures?

Answer 37

secondary structure (held by weak h2 bonds to form a and be sheets
tertiary structure; 3d shape stabilised by side chain interactions
quaternary structure; multiple proteins associate tgt to form a functional protein

Question 38

where does translation commence?

Answer 38

free ribosomes. (proteins that are destined to function in the cytosol.

Question 39

how do signal peptides direct ribosomes to rer

Answer 39

1. srp binds to signal peptide
2. srp binds to receptor protein
3. erp detaches and polypeptide synthesis resumse
4. signal cleaving enzyme cuts off signal peptide
5. polypeptide folds into final conformation.

Question 40

post-translational modifications

Answer 40

phosphorylation
methylation
acetylation
biotinylation
carboxylation
carbohydrate addition
cleavage
ubiquitination.