8.4- POLYPEPTIDE SYNETHESIS- TRANSCRIPTION AND SPLICING

Question 1

What is the basic process of the production of proteins in a cell? (3)

Answer 1

DNA provides instructions in form of long sequence of bases

complementary section of part of this sequence made in form of molecule called pre-mRNA- process called transcription

pre-mRNA spliced to form mRNA

mRNA used as template to which complementary tRNA molecules attach + amino acids they carry linked to form polypeptide- process called translation

Question 2

What is transcription?

Answer 2

process of making pre-mRNA using part of DNA as template

Question 3

transcription #1

Answer 3

enzyme acts on specific region of DNA causing two strands to separate + expose nucleotide bases in that region

Question 4

transcription #2

Answer 4

nucleotide bases on one of two DNA strands, known as template strand, pair with their complementary nucleotides from pool present in nucleus
enzyme RNA polymerase then moves along strand + joins nucleotides together to form pre mRNA molecules

Question 5

transcription #3

Answer 5

guanine on DNA binds to cytosine base of free nucleotide
cytosine links to guanine, + thymine joins to adenine
exception is adenine, which links to uracil rather than thymine

Question 6

transcription #4

Answer 6

as RNA polymerase adds nucleotides one at a time to build strand of pre-mRNA, DNA strands re-join behind it
so only about 12 base pairs on DNA exposed at any one time

Question 7

transcription #5

Answer 7

when RNA polymerase reaches particular sequence of bases on DNA that recognises as ‘stop’ triplet code, it detaches, + production of pre-mRNA complete

Question 8

In prokaryotic cells, what does transcription directly result to?

Answer 8

results directly in production of mRNA from DNA

Question 9

In eukaryotic cells, what does transcription result in?

Answer 9

results in production of pre-mRNA

Question 10

What happens to pre-mRNA in the eukaryotic cells?

Answer 10

spliced to form mRNA

Question 11

What is the DNA of a gene eukaryotic cells made up of?

Answer 11

sections called exons + introns

Question 12

What are exons?

Answer 12

section of DNA that codes for proteins

Question 13

What are introns?

Answer 13

section of DNA that doesn’t code for proteins

Question 14

What do introns prevent?

Answer 14

synthesis of polypeptide

Question 15

What is splicing?

Answer 15

base sequences corresponding to introns removed + functional exons joined together

Question 16

Why is splicing unnecessary in prokaryotic cells?

Answer 16

prokaryotic cells don’t have introns

Question 17

What is the mRNA molecule too big to do?

Answer 17

to big to diffuse out of nucleus

Question 18

As the mRNA molecules are too large to diffuse out of the nucleus, what happens once they’ve been spliced?

Answer 18

leave via nuclear pore

Question 19

What happens to the mRNA outside the nucleus?

Answer 19

mRNA attracted to ribosomes to which it becomes attached, ready for next stage of process: translation