DNA, RNA and protein synthesis: RNA and protein synthesis

Question 1

What are the two types of RNA involved in protein synthesis

Answer 1

mRNA and tRNA

Question 2

What are the tree types of RNA (and briefly outline their roles)

Answer 2

• mRNA (messenger RNA)
• tRNA (transfer RNA)
• rRNA (Ribosomal RNA)

Question 3

How does RNA differ from DNA

Answer 3

• RNA a a single polynucleotide chain
• RNA contains uracil which is a replacement for thymine in DNA

Question 4

What does uracil always pair with during protein synthesis

Answer 4

Adenine

Question 5

When is mRNA made

Answer 5

During transcription

Question 6

Outline the features of mRNA as polynucleotide involved in protein synthesis

Answer 6

• It is a single polynucleotide chain made during transcription
• Synthesised through the formation of phosphodiester bonds between 5-c of one ribose with 3-c of an adjacent RNA molecule
• It carries the genetic code from the nucleus to the ribosomes, where it is used to make a protein during translation.
• They contain groups of three adjacent bases called called codons (sometimes called triplets or base triplets)

Question 7

Outline tRNA as a polynucleotide involved in protein synthesis

Answer 7

• It is a single polynucleotide strand folded into a clover shape with hydrogen bonds between complementary base pairs holding the molecule in this shape
• tRNA is involved in translation
• Responsible for carrying the amino acids that are used to make proteins to the ribosomes
• Every tRNA molecule has a specific sequence of three bases at one end called an anticodon

*Every tRNA molecule also has an amino acid binding site at the other end

Question 8

What are the two processes of protein synthesis

Answer 8

• Transcription
• Translation

Question 9

What is the first step in protein synthesis

Answer 9

Transcription

Question 10

What is the seconds step in protein synthesis

Answer 10

Translation

Question 11

Describe the processes that occur during transcription

Answer 11

• RNA polymerase attaches to the initiation site of the DNA double helix at the beginning of a gene
• In eukaryotes the hydrogen bonds holding the DNA strands together are broken by a DNA helicase attached to RNA polymerase separating and uncoiling the strands, exposing some of the bases
• One of the strands is then used as a template to make an mRNA copy
• RNA polymerase lines up free RNA nucleotides along exposed bases on template strand. The free bases are attracted to the exposed bases and they attach to their complimentary base
• Once attached, they are joined together by RNA polymerase, forming an mRNA molecule
• RNA polymerase moves along DNA, separating the strands and assembling the mRNA strand
• Hydrogen bonds reform once RNA polymerase has passed and coils back into double helix
• When RNA reaches a stop signal, it stops making mRNA and detaches
• mRNA moves out of nucleus through nuclear pore and attaches to ribosome

Question 12

What is pre-mRNA

Answer 12

mRNA strands containing both introns and exons

Question 13

What process occurs to remove the introns in pre-mRNA

Answer 13

Splicing

Question 14

What is splicing

Answer 14

• When the introns from pre-mRNA are removed and the exons are joined together - creating mRNA

Question 15

Why does splicing not occur in prokaryotic cells

Answer 15

• Bc mRNA is produced directly from the DNA as there are no introns in prokaryotic DNA

Question 16

Where and when does splicing occur

Answer 16

• It occurs in the nucleus before translation occurs (it occurs post transcription)