3.4.2 DNA And Protein Synthesis

Question 1

What is RNA?

Answer 1

RNA is a polymer made up of nucleotides formed of a ribose sugar, a nitrogenous base and a phosphate group.

Question 2

What are the RNA bases?

Answer 2

Adenine
Cytosine
Guanine
Uracil

Question 3

What is the function of RNA?

Answer 3

To copy and transfer the genetic code from the DNA in the nucleus to the ribosomes to synthesise proteins.
Some RNA is combined with proteins to create ribosomes.

Question 4

What is mRNA?

Answer 4

A copy of a gene from DNA made during transcription

Question 5

How is mRNA made?

Answer 5

From the anti-sense strand of DNA in the nucleus, before diffusing out of the nucleus through nuclear pores

Question 6

Why can mRNA get out of the nucleus but DNA can’t?

Answer 6

MRNA only contains the base sequence for one gene, so is much smaller than DNA and is able to diffuse out of the nuclear pores.

Question 8

Why is mRNA short lived?

Answer 8

It is easily broken down/hydrolysed by enzymes, so does not remain outside of the cell when not needed.

Question 9

What is a codon?

Answer 9

A triplet of bases on the mRNA molecule that codes for a specific amino acid in the polypeptide chain.

Question 10

Is RNA single or double stranded?

Answer 10

Single stranded

Question 11

What does mRNA stand for?

Answer 11

Messenger RNA

Question 12

What does tRNA stand for?

Answer 12

Transfer RNA

Question 13

What is tRNA?

Answer 13

The type of RNA which attaches to and transfers specific amino acids to the ribosome to create a polypeptide chain.

Question 14

What is the role of tRNA?

Answer 14

To attach to and carry amino acids from the cytoplasm to ribosomes in translation

Question 15

What is the shape of tRNA and how is it held together?

Answer 15

It is a cloverleaf shape that is held in place by hydrogen bonds.

Question 16

What is the anticodon of tRNA?

Answer 16

A sequence of 3 bases that are complementary to the 3 bases on mRNA, so the specific amino acids are arranged in the correct order.

Question 17

What does rRNA stand for?

Answer 17

Ribosomal RNA

Question 18

What is rRNA?

Answer 18

A type of RNA that combines with a protein to make a ribosome.
It is non-coding so has no coding information, but acts as an anchor to force mRNA through the ribosome during translation.

Question 19

What is protein synthesis?

Answer 19

The process by which proteins are formed from amino acids, that consists of two stages: transcription and translation

Question 20

What is transcription?

Answer 20

The first stage of protein synthesis where the base sequence on a particular gene is copied onto mRNA in the nucleus.

Question 21

What is translation?

Answer 21

Where the mRNA Jon’s with a ribosome, and corresponding tRNA molecules bring the specific amino acids that a codon codes for.

Question 22

What is the proteome?

Answer 22

The entire set of proteins that an organism codes for and synthesises.

Question 23

Where does transcription take place?

Answer 23

In the nucleus

Question 24

Describe the process of transcription

Answer 24

DNA helicase unwinds the double helix by breaking hydrogen bonds between bases, so complementary base pairs are broken.
Free RNA nucleotides bind to the exposed bases on the DNA anti-sense strand by complementary base pairing.
RNA polymerase joins RNA nucleotides to create pre-mRNA (a copy of one entire gene).
When the codon that signals to stop is reached, the RNA polymerase detaches and the DNA strand reforms its original double helix shape.

Question 25

What type of cells does splicing occur in?

Answer 25

Eukaryotic cells

Question 26

What are introns?

Answer 26

Sections of DNA which are non-coding for amino acids, and therefore not expressed in the final protein

Question 27

What are exons?

Answer 27

Coding sections of DNA that code for a specific amino acid, so are expressed in the final protein.

Question 28

Describe the process of splicing

Answer 28

An enzyme called splice some removes the base sequence corresponding to the introns, as they do not code for the synthesis of the polypeptide. Splicing joins the exons together to form mRNA from pre-mRNA.

Question 29

What happens after splicing?

Answer 29

The mRNA molecule now moves out of the nucleus via the nuclear pores, and binds to the ribosomes in the cytoplasm.

Question 30

By what process does mRNA leave the nucleus?

Answer 30

Diffusion- as it moves from a high to low concentration

Question 31

Describe the process of translation

Answer 31

mRNA attaches to a ribosome in the cytoplasm. The ribosome attaches to the start codon on the mRNA. The tRNA molecules with the complementary anticodon to the codon on mRNA bring the specific amino acids to the mRNA molecule.. The amino acids then join by peptide bonds, which requires energy from ATP. This continues until the stop codon is reached, when the ribosome detaches and translation ends.

Question 32

What happens after translation?

Answer 32

The polypeptide chain is now synthesised and will enter the Golgi body for folding and modification.

Question 33

What are the similarities between transcription and translation?

Answer 33

They both involve complementary base pairing They both involve enzymes They both involve the formation of bonds

Question 34

What are the differences between transcription and translation?

Answer 34

Transcription takes place in the nucleus, whereas translation takes place in the cytoplasm. Transcription does not involve tRNA but does involve mRNA, whereas translation involves both mRNA and tRNA. Transcription involves both DNA and RNA, whereas translation involves RNA only. Transcription involves the joining of free nucleotides, whereas in translation, nucleotides are already assembled. In transcription, mRNA contains introns, whereas, in translation, mRNA does not contain introns. In transcription, no proteins are made, whereas in translation, proteins are made by assembling amino acids. In transcription, phosphodiester bonds are formed, whereas in translation, peptide bonds are formed. In transcription, the enzymes DNA helicase and RNA polymerase are needed, whereas translation requires the enzyme peptidyl transferase.