3.4.2 DNA and protein synthesis

Question 1

what is DNA?

Answer 1

deoxyribose nucleic acid

contains instructions on how to build proteins used in the body

found in cell nucleus and used for individual proteins

made up from chain of sugar-phosphates and one of four bases

Question 2

what are proteins?

Answer 2

polymer of units linked by peptide bonds

built from 20 amino acids

created in ribosomes

perform these functions =
1. enzymes
2. antibodies
3. structural bodies
4. hormones

Question 3

how is DNA moved around the body?

Answer 3

DNA cannot escape the nucleus, the molecule are too large and proteins are manufactured in ribosomes outside the nucleus envelope

uses an intermediary form messenger RNA (MRNA)

Question 4

what is the definition of transcription?

Answer 4

formation of pre-MRNA from DNA through complementary base pairing

Question 5

describe the transcription process

Answer 5

1. DNA helicase (enzyme) breaks H bonds between nucleotides of DNA
2. this causes the two strands to seperate and expose the nucleotide bases in that region. Only about 12 bases pair on the DNA are exposed at anyone time.
3. RNA polymerase moves along a template strand and makes pre-MRNA using complimentary base pairing, from the pool present in the nucleus
   - adenine in DNA binds to Uracil in pre-MRNA, not Thymine
4. DNA strands rejoin behind RNA polymerase
5. DNA polymerase reaches stop codons (triplet base code) and detaches and the production of pre-MRNA is then complete

Question 6

how is pre-MRNA spliced?

Answer 6

Sections of DNA are non-coding “Junk DNA”

introns in pre-MRNA would interfere with polypeptide synthesis — needs removing by splicing

non functional introns are removed and functioned exons joined together

exons can rejoin in a variety of combinations - one gene can code for more than one protein depending on exon recombing

mutations altering preMRNA splicing can lead to non-functional polypeptides being made eg alzeimers

Question 7

what is splicing?

Answer 7

changing pre-MRNA to form MRNA

Question 8

what is translation?

Answer 8

mRNA + T-RNA are used to translate the genetic code into the polypeptide code to form proteins

Question 9

give a definition of introns

Answer 9

non coding regions

Question 10

what is the definition of exons?

Answer 10

coding regions of DNA

Question 11

describe the process of protein synthesis

Answer 11

1. DNA provides the instructions in the form of a long sequence of nucleotides and bases they process.
2. A complimentary section part of this sequence is made in the form of a molecule called pre-MRNA
3. The pre-MRNA is modified to mRNA by removing the base sequences copied from no-functional DNA (introns)
4. The mRNA is used as a tempate to which complimentary tRNA molecules attach and the amino acids they carry are linked to form a polypeptide
5. The pre-mRNA molecules are too large to diffuse out of the nucleus and so once they have been spliced, they leave via a nuclear pore.

Question 12

translation

Answer 12

translation is the process in which mRNA is read and translated into a protein

occurs on ribosomes

process involves another type of RNA molecule known as transfer TRNA

tRNA is present in the ER as tRNA amino acids complexes

tRNA is specific to each amino acid

three bases at the bottom of the tRNA and a amino acid at the other

Question 13

translation process

Answer 13

1. MRNA leaves the nucleus through a nuclear pore and enters the cytoplasm
2. ribosomes become attached to the mRNA; genetic code on the MRNA is read in groups of 3 letters = codons
3. tRNA molecules have specific antibodies for each of the 20 amino acids
4. the complimentary anticodon is attached to the first codon on the mRNA and forms a weaker hydrogen
5. the second codon on mRNA also attracts its complimentary anticodon on tRNA
6. a peptide bond is formed between adjacent amino acids
7. the first tRNA molecule becomes detached from it’s amino acid
8. ribosomes move along the MRNA molecule
9. third tRNA moves in place the anticodon linking with it’s complimentary codon
10. a peptide bond forms between the two amino acids
11. a polypeptide chain has been formed and is released into the cytoplasm
12. several ribosomes may pass along the mRNA behind the first - each producing an identical polypeptide
13. tRNA molecules are activated after use by recombing with their specific amino acid

Question 14

anti codon definition

Answer 14

triplet of bases on the tRNA