Topic 4- DNA and protein synthesis

Question 1

What is the genome?

Answer 1

The complete set of genes in a cell.

Question 2

What is the proteome?

Answer 2

The full range of proteins that a cell is able to produce.

Question 3

Describe the structure of RNA.

Answer 3

RNA is a polymer formed of a ribose, nitrogenous base and a phosphate group.

Question 4

What are the nitrogenous bases in RNA?

Answer 4

Adenine
Uracil
Cytosine
Guanine

Question 5

how is the RNA polymer different to DNA?

Answer 5

The RNA polymer is relatively short and single strangled and has the base uracil instead of thymine.

Question 6

What is the function of RNA?

Answer 6

To copy and transfer the genetic code from DNA in the nucleus to the ribosomes.

Question 7

What is mRNA?

Answer 7

A copy of a gene from DNA.

Question 8

Where is mRNA created and what does it do?

Answer 8

The nucleus. It then leaves the nucleus to carry the copy of the genetic code of one gene to the ribosomes in the cytoplasm.

Question 9

Why can DNA not leave the nucleus?

Answer 9

DNA is too large to leave the nucleus and would be risk of being damaged by enzymes, therefore destroying the genetic code permanently.

Question 10

Why does mRNA leave the nucleus instead?

Answer 10

mRNA is much shorter, as its only the length of one gene.

Question 11

Why is mRNA short lived?

Answer 11

It is only needed temporarily to help create a protein, therefore by the time any enzyme could break it down it has already carried out its function.

Question 12

What is the structure of mRNA?

Answer 12

It has single a polynucleotide strand.
Three adjacent bases form a group in mRNA, which is known as codons.

Question 13

Where is tRNA found?

Answer 13

Cytoplasm.

Question 14

What is the structure of tRNA?

Answer 14

single stranded polynucleotide that’s folded to form a cloverleaf shape held together by hydrogen bonds between specific base pairs. They have specific sequence of three bases called and anticodon. At the other end it has an amino acid binding.

Question 15

What is the function of tRNA?

Answer 15

It is involved in translation. It attaches to one of the 20 amino acids and transfer this amino acid to the ribosome to create the polypeptide chain.

Question 16

How does tRNA attach to a specific amino acid?

Answer 16

Specific amino acids attach to specific tRNA molecules determined by 3 bases found on the tRNA which are complementary to the 3 bases on mRNA.

Question 17

Why are the sequences on tRNA molecules referred to as anticodons?

Answer 17

They’re complementary to the codons on mRNA.

Question 18

What does rRNA do?

Answer 18

Combines with protein to make a ribosome.

Question 19

What is the difference between the DNA and RNA monomers?

Answer 19

DNA contains the base thymine, whereas RNA contains uracil instead.
DNA contains the pentose sugar deoxyribose whereas RNA contains the pentose sugar ribose.

Question 20

What is the difference between the DNA and RNA polymers?

Answer 20

DNA is much larger as it contains approximately 23,000 genes (the entire genome), whereas RNA is much shorter as its only the length of one gene.
DNA is double stranded, whereas RNA is single stranded.

Question 21

What is transcription?

Answer 21

The production of mRNA from DNA. In eukaryotic cells, transcription takes place in the nucleus. In Prokaryotes takes place in the cytoplasm.

Question 22

What is translation?

Answer 22

Translation is the second stage of protein synthesis. This where the mRNA joins with a ribosome joined together to make a polypeptide chain, following the sequence of codons carried by the mRNA.

Question 23

What is the 1st step of transcription?

Answer 23

At the start of transcription, RNA polymerase attaches to the DNA double helix at the beginning of a gene. In eukaryotes the hydrogen bonds between the 2 DNA strands in the gene are broken by DNA helicase attached to the RNA polymerase. This separates the strands and the DNA molecule uncoils, exposing some of the bases.
One of the strands is then used as a
template to make an mRNA copy.

Question 24

What is the 2nd step of transcription?

Answer 24

The RNA polymerase lines up free RNA nucleotides alongside the exposed bases on the DNA template strand. The free bases are attracted to the exposed bases. Specific complementary base pairing, means the mRNA is a complementary copy of the DNA template strand, (except the base T is replaced with U in RNA). Once the RNA nucleotides have paired up with their specific bases on the DNA strand, they are joined together by RNA polymerases forming an mRNA strand.

Question 25

What is the 3rd step of transcription?

Answer 25

The RNA polymerases moves along the DNA, assembling the mRNA strand. The hydrogen bonds between the uncoiled strands of DNA reforms once the RNA polymerase has passed by and coils back into a double helix.

Question 26

What is the final step of transcription?

Answer 26

When RNA polymerase reaches a particular sequence of DNA, called the stop signal, it stops making mRNA and detaches from the DNA. In eukaryotes mRNA moves out of the nucleus through nuclear pores and attaches to a ribosome in the cytoplasm where the next stage of protein synthesis takes place.

Question 27

What is pre-mRNA?

Answer 27

mRNA strands containg both introns and exons.

Question 28

What process occurs to remove the introns and where?

Answer 28

Splicing occurs when the introns are removed and the exons are joined together. This creates functional mRNA strands. This takes place in the nucleus before translation occurs.

Question 29

Why is splicing not necessary in prokaryotic cells?

Answer 29

There’s no introns in prokaryotes. mRNA is produced directly from the DNA.

Question 30

What are the steps of translation?