Lecture 9 - gene to protein

Question 1

3 main steps of gene expression

Answer 1

Transcription, where DNA is copied into pre-mRNA; Processing, where pre-mRNA is checked/fixed; Translation, where protein is made from mRNA instructions

Question 2

Transcription process

Answer 2

1.) During Initiation, polymerase binds to promotor 2.) During Elongation, polymerase transcribes RNA moving downstream 3.)During Termination, detachment upon reaching terminator region.

Question 3

RNA vs DNA

Answer 3

RNA single while DNA double stranded; RNA pairs Adenine/Uracil while DNA pairs Adenine/Thymine

Question 4

Transcription Initiation Complex

Answer 4

RNA polymerase II and several associated Transcription factors (proteins)

Question 5

Where do Transcription Factors bind on DNA

Answer 5

At the TATA box in the promotor region

Question 6

How many nucleotides are exposed when DNA is unwound?

Answer 6

10-20 nucleotides

Question 7

Elongation process transcription

Answer 7

Complementary nucleotides to the template strand of DNA are added to 3’ end of new pre-mRNA. Double helix reforms as polymerase II leaves. Phosphodiesterase bonds form between 3’OH and 5’ phosphate.

Question 8

Termination process transcription

Answer 8

Once AAUAAA has been transcripted, pre-mRNA released from nuclear enzymes and

Question 9

3 modifications in processing and purpose

Answer 9

Capping, Tailing, Splicing allows for stability, export, ribosome binding

Question 10

Capping

Answer 10

1 modified Guanine is added to 5’ end

Question 11

Tailing

Answer 11

50-250 Adenine nucleotides are added to 3’ end (polyA tail)

Question 12

Splicing

Answer 12

Spliceosomes cut out introns and splice exons together with cap and tail

Question 13

Exons vs Introns

Answer 13

Exons are kept in mRNA and between untranslated regions (UTR) while introns are cut out

Question 14

Spliceosome components

Answer 14

large complex of proteins and small RNAs

Question 15

A codon is a…

Answer 15

Set of 3 bases coding for a specific amino acid. Some examples: start = AUG, UAA or UAG or UGA = stop

Question 16

Translation

Answer 16

tRNA brings amino acid to ribosome, if complementary to the next codon hydrogen bonding forms between mRNA and anti codon. Amino acid forms peptide bonds with polypeptide chain.

Question 17

tRNA structure/function

Answer 17

anti codon corresponds to amino acid; physical link between mRNA and amino acid sequence

Question 18

Ribosome structure translation

Answer 18

In large unit, A site for tRNA waiting line, P site for tRNA adding aa to polypeptide, E site for tRNA exit.

Small unit for binding of mRNA

Question 19

Assemble of ribosome, mRNA, tRNA

Answer 19

Needs GTP. Initiator RNA (methionine/Met) ) added to small unit of ribosome, small uni scans for start codon and hydrogen bonds form mRNA/ini tRNA, large unit binds

Question 20

4 control points of gene expression

Answer 20

Transcription factors need to be assembled, processing of pre-mRNA, export of mRNA thru nuclear pores reg by specific proteins, regulatory proteins can block translation/ mRNA life spans

Question 21

Translocation in translation elongation

Answer 21

movement of tRNA thru A-P-E

Question 22

what enzyme refills tRNA

Answer 22

aminoacyl-tRNA synthetase

Question 23

GTP function in gene expression

Answer 23

Gtp for assembling of translation complex,2 GTP used to disassemble translation complex, increases efficiency and accuracy of codon recognition

Question 24

Level of structures

Answer 24

Primary - protein sequence; secondary - alpha helixes/beta sheets; tertiary - 3D; quaternary - multiple proteins associate to form protein

Question 25

Primary structure of protein

Answer 25

NH3 is N-terminus is 5’ end, COOH is C-terminus is 3’ end; amino acids bonded with relatively strong covalent bonds

Question 26

Secondary structure of protein

Answer 26

Alpha helixes or beta sheets from weak hydrogen bonds

Question 27

Tertiary and quaternary structure of protein

Answer 27

tert- 3D shape stabilised by side chain interactions; quat - not all proteins form quaternary

Question 28

Signal peptides process

Answer 28

Protein synthesis starts until signal peptide at N-terminus reached –> Signal recognition particle (SRP) binds to signal peptide + signal receptor protein then leaves–> finish synthesis then enzyme cleaves protein from receptor protein –> protein folds

Question 29

post translation modifications

Answer 29

may occur in golgi appartus or cytosol
- _____ylation = adding ____
- carbohydrate addition = adding carb (glycoprotein for cell recognition)
- cleavage
- ubiquitination = degradation

Question 30

post translational- purpose/location

Answer 30

Allow for interaction with other molecules, activation, direct to particular locations

Question 31

Signal receptor particles binds where?

Answer 31

At N terminus when there is a signal peptide of approximately 20 amino acids

Question 32

Where do secretory proteins and membrane peptides go after translation

Answer 32

Golgi apparatus for further modification and maturation. Secretory proteins are solubilsed in RER lumen