dna

Question 1

how many genes are used to make a human

Answer 1

20,000

Question 2

3 properties of RNA that allow it to function as an enzyme

Answer 2

• can form 3d structures - can base pair with itself
• RNA base pairs contain functional groups
• RNA may be targeted to a location as it can hydrogen bond with other nucleic acids

Question 3

what happens to mRNA before the genetic messages are dispatched to the cytoplasm

Answer 3

Enzymes in the nucleus modify pre-mRNA

Question 4

2 alterations of mRNA ends

Answer 4

Each end of a pre-mRNA molecule is modified in a particular way:
1. 5’ end -> 5’ cap (a modified guanine nucleotide)
2. 3’ end -> poly-A tail (50-250 adenine nucleotides)

Question 5

what are introns

Answer 5

long noncoding stretches of nucleotides that lie between coding regions in genes and RNA transcripts

Question 6

what are exons

Answer 6

expressed parts of the genes/RNA - usually translated into amino acid sequences later

Question 7

what is RNA splicing

Answer 7

removes introns and joins exons - makes molecule with a continuous coding sequence
- occurs in spliceosomes

Question 8

what are ribosomes

Answer 8

• Ribosomes facilitate specific coupling of tRNA anticodons with mRNA codons in protein synthesis
• The 2 ribosomal subunits (large and small) are made of proteins and ribosomal RNA (rRNA)

Question 9

ribosomes 3 binding sites for tRNA

Answer 9

1. P site - holds the tRNA that carries the growing polypeptide chain (growing chain)
2. A site - holds the tRNA that carries the next amino acid to be added to the chain (waiting room)
3. E site - exit site, where discharged tRNAs leave the ribosome

Question 10

what is tRNA

Answer 10

• helps translate an mRNA message into protein
• consists of a single RNA strand ~80 nucleotides long
• not identical: specific a.a on one end + anticodon on other end
• 3d L shaped + 2d clover shaped

Question 11

2 steps of accurate translation

Answer 11

1. a correct match between a tRNA + an amino acid - done by aminoacyl-tRNA synthetase
2. a correct match between the tRNA anticodon + an mRNA codon

Question 12

what is WOBBLE

Answer 12

Flexible pairing at the third base of a codon - allows some tRNAs to bind to more than one codon

Question 13

3 stages of translation

Answer 13

i. initiation
ii. Elongation
iii. Termination

Question 14

what happens in translation initiation

Answer 14

• brings together mRNA, tRNA, and the 2 ribosomal subunits - TRANSLATION INITIATION COMPLEX
  1. small subunit binds the mRNA with special initiator tRNA
  2. it moves along RNA until it binds AUG codon
  3. initiation factors bring in large subunit

Question 15

what happens in translation elongation

Answer 15

amino acids are added one by one to the proceeding amino acid
- each addition uses ELONGATION FACTORS + occurs in 3 steps:
1. codon recognition
2. peptide bond formation
3. translocation

Question 16

what happens in translation termination

Answer 16

occurs when a stop codon reaches the A site of the ribosome
- A site accepts a protein called a RELEASE FACTOR which adds H2O instead of an a.a - causes translation assembly to fall off

Question 17

what can happen after a polypeptide is made

Answer 17

• post translation modifications e.g. add functional groups
• targeted to different locations:
• translated by free ribosomes = stays local
• translated by ribosomes on ER = packaged to go to other locations - marked with a signal peptide that are recognised by SIGNAL RECOGNITION PARTICLE??