9&10 → Genotype To Phenotype

Question 1

Evidence that genes code for proteins?

Answer 1

Beagle & Tatum
Used X-rays as mutagens to knock out genes in the bread mould → neurospora
Neurospora = haploid Ca set of chromosome
No 2nd copies of genes to back up
Wild type neurospora → prototroph
Selected mutants that were autotrophs
Arg mutant strains → had to be supplied with AA arginere

Question 2

Experiment → enzymes

Answer 2

??????

Question 3

What is the evidence that genes code flor proteins?

Answer 3

I gene, I polypeptide relationship

Question 4

What is the central dogma of molecular bio

Answer 4

Information flows in 1 direction from DNA to protein’s when gens are expressed
DNA → RNA → polypeptide
(Francis crick )

Question 5

Define RNA?

Answer 5

One strand
Ribose sugar

Uracil instead of thymine
Can fold into complex shapes by internal base pairings

Question 6

A string of amino acids

Answer 6

From what??????

Question 7

String of nucleotides to a protein?
A string of amino acids

Answer 7

Protein synthesis involves two steps →
Transcription of an RNA copy and then translation of RNA to protein

Question 8

What is transcription?

Answer 8

Prod mRNA which will go on and be translated into protein
Essentially the same

Question 9

Stage 1→ initiation

Answer 9

A region of DNA upstream of the protein coding sequence cared a promoter attracts RNA polymerase
The promoter tells RNA polymerase where to start/ which direction to go in.
Genes can be adjusted in either direction on DNA ( strands antiparralen )
Coding strand: runs 5’ → 3’
RNA polymerase binds to the promoter and stats to unwind DNA strand.
Actual coding sequence begins

Question 10

2. Elongation

Answer 10

RNA polymerases makes a RNA copy of the coding ‘
Strand of DNA double helix by reading the template strand
RNA polymerases reads the DNA template strand from 3’ to 5’ and produces the RNA transcript by adding nucleotides to 3’ end.
RNA polymerase unwinds DNA about 10 base pairs at a time → open complex
Open complex= makes unpaired base with DNA available to pair with ribonucleic
& RNA synthesis begins

Question 11

3. Termination

Answer 11

When RNA polymerase reaches the termination site, the RNA transcript is set tree from the template
RNA polymerase recognises lt and falls Off the DNA natantly
Specified by specific base sequence

Question 12

What 2 factors are required by translation?

Answer 12

Rib os ones
tRNA

Question 13

Define ribosomes?

Answer 13

Holds mRNA in correct position to allow assembly of polypeptide chain
Ribosomes → can make any protein
2 subunits, large and small
Subunits held together by ionic and hydro phobic forces
Notactivein translation → they exist separately
Mostly RNA

Question 14

What are transfer RNA?

Answer 14

Adaptor molecules that can bind amino acids and recognise a nucleotide sequence
tRNA carrying amino acids line up on mRNA in proper sequence for poly peptic chai
→ predicted by adapted hypothesis
Each AA → specific type tRNA
75 - 80 nucleotides
3’ end is amino acid attachment site _ covalent

Question 15

Amino - acyl tRNA syntheses?

Answer 15

tRNAs → loaded with correct AA by activating enzymes called amino-acyl tRNA synthetics
Each enzyme → specific for 1 AA and corresponding tRNA
AA attached to tRNA by energy-rich bond -
→ provide energy for synthesis of peptide band to join AA

Question 16

How is the code deciphered?

Answer 16

Proteins= 20 diff amino acids
AA written with only 4 letters ( nucleotides )
A doublet nucleotide codes → 4x4=16 code words
Triplet nucleoliche codes → 4x4x4 = 64 code words
Enough codes to 20 AA

Question 17

Genetic code deciphering experiment?

Answer 17

Nirenburg and mattharei
Hypothesis= A triplet codon based om 3 - base codons specifies AA
???????

Question 18

Define universal?

Answer 18

The genetic code is the same and is shared by all life
Animals /humans etc

Question 19

Define redundant?

Answer 19

When more than 1 codon can code for the same amino acid.

Question 20

Define unambiguous?

Answer 20

The same codon wee always encode the same AA

Question 21

What do transfer RNAs have that is complimentary to the codon for specific amino acids?.

Answer 21

Anticodon
Amino acid attachment site → 3’ end
Hydrogen bonds with 3’ and 5’ resulting in 3D structure
Eq.)
Anticodon = arginine
DNA coding strand → 5’ - CG G - 3’
DNA template strand → 3’ GCC - 5’
mRNA → 5’ - CGG - 3’
Anticodon on the tRNA → 3’- gcc-5’
Erna charged with argineve

Question 22

How is redundancy of the code made possible?

Answer 22

Wobble: specificity for base at 3’ end of codon is not always observed

Question 23

How is RNA translated into proteins?

Answer 23

Initiation
Elongation
termination

Question 24

The initiation of translation?

Answer 24

Ribosomes have 3 tRNA binding sites:
Amino site binds with anticodon of charged tRNA
Polypeptide site is where tRNA adds its AA to growing chains
EXI T- site is where Erna sits before being released

Question 25

The initiation of translation?.
Part 2

Answer 25

The small subunit binds first on mRNA
Then the tRNA carrying the first AA → always methionine
(Aug)
Large subunit binds so that first tRNA is bound in P site

Question 26

The elongation of trans latter?

Answer 26

2nd charged tRNA enters the A site
Large subunit was peptidyl transferase activity ‘
Breaks bonds between tRNA in P site I its AA
Forms peptide bonds between amino acid & AA on tRNA in A site
→ 1st tRNA has released its methionine ribosome moves along by 1 codon
→ The tRNA now at the e site dissociate from ribosome
Process continues

Question 27

How does termination of translation occur?

Answer 27

A release factor → binds to the stop codon
Allowing hydrolysis of bond between polypeptide chain and tRNA.
The ribosome diss associates