Protein Synthesis

Question 1

Where is RNA made?

Answer 1

• in the nucleus

Question 2

What are the different types of RNA?

Answer 2

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

Question 3

What is transcription?

Answer 3

• the process by which DNA makes and codes mRNA
• mRNA is formed in the nucleus in the same way as DNA is replicated
• the coded message in DNA is transcribed into the new mRNA molecule, which carries it to the ribosome

Question 4

What is a protein?

Answer 4

• a long chain (polymer) of small units (monomers) called amino acids

Question 5

How many different amino acids are involved in protein synthesis?

Answer 5

• 20

Question 6

How do amino acids create proteins?

Answer 6

• they combine in various numbers in various sequences to form thousands of different proteins

Question 7

How many amino acids does the shortest protein chain have?

Answer 7

• 50 amino acids

Question 8

How is the kind of protein that amino acids make, determined?

Answer 8

• the order in which the amino acids are linked determines what kind of protein is made

Question 9

What is the role of mRNA?

Answer 9

• mRNA receives the instructions from the genetic code in the DNA molecules, which determines the sequence of amino acids

Question 10

How is the genetic code carried and what is this genetic code made up of?

Answer 10

• genetic code is carried as a sequence of ‘codewords’ which are transcribed to the mRNA
• each ‘codeword’ is made up of any 3 bases, and is called a codon
• eg, cytosine + adenine + guanine

Question 11

How many codons are there and what do they do?

Answer 11

• there are 64 different codons
• 61 of them code for one of the 20 amino acids used to form proteins
• some amino acids are coded for by more than one codon

Question 12

What are the 3 codons that don’t code for an amino acid? What are they called?

Answer 12

• UGA, UAA & UAG
• these are called ‘stop codons’

Question 13

How is a codon written?

Answer 13

• using the first letter of each of the different bases

Question 14

What is the triplet code of bases?

Answer 14

• the basis of the genetic code
• as a gene is made up of a group of 3 codons that code for the synthesis of one protein

Question 15

What does the order of codons in mRNA determine?

Answer 15

• the order of codons in mRNA will therefore determine the sequence of the amino acids
• which which determine which protein is made

Question 16

What happens at the ribosomes in protein synthesis?

Answer 16

• the mRNA binds to the ribosome at the start codon (1st codon)
• the codons of the mRNA act as a template that determines the order in which the amino acids are linked

Question 17

How many tRNA molecules are there and what are they made from?

Answer 17

• at least 64 different tRNA molecules
• made from nucleotides found in the cytoplasm of cells

Question 18

What does each tRNA have?

Answer 18

• three bases at one end called an anti-codon

Question 19

What does an anti-codon do?

Answer 19

• picks up a specific amino acid found in the cytoplasm and transfers it to a ribosome

Question 20

What is the most important feature of tRNA?

Answer 20

• it can bind to an amino acid at one end and bind to mRNA at the other
  -> depositing its amino acid in the correct position to form a specific protein

Question 21

How does the process of making a protein from amino acids begin?

Answer 21

• one of the codons, the ‘start signal’ begins the process

Question 22

How do the amino acids know when the protein chain is complete?

Answer 22

• three codons act at ‘stop signals’
• they indicate that the message is over and the protein chain is complete

Question 23

What is an anticodon base?

Answer 23

• the complementary base to a codon base
• eg, if the codon of mRNA is GGA, the anticodon of the tRNA will be CCU

Question 24

What is translation?

Answer 24

• the process by which a specific protein is formed from a chain of amino acids due to the sequence of codons in the mRNA, which, in turn, was coded by the DNA

Question 25

What are the two stages of protein synthesis?

Answer 25

1. transcription: the copying of the DNA code onto mRNA in the nucleus 2. translation: the formation of protein molecules on the ribosomes using tRNA

Question 26

What is the role of rRNA?

Answer 26

- the most common form of RNA in the cell - together with proteins, makes up the ribosomes

Question 27

What does rRNA do?

Answer 27

- moves from codon to codon along the mRNA, reading the code

Question 28

What does rRNA play an important role in doing?

Answer 28

- rRNA plays an important role in controlling the process of protein synthesis

Question 29

How do antibiotics counteract bacterial infections?

Answer 29

- by interacting with the bacterial ribosomes and inhibiting their function of protein synthesis - if bacteria are prohibited from making proteins (which are essential for the production and growth of new cells) then they will not be able to make new cells to spread the infection

Question 30

What are the different antibiotics that inhibit protein synthesis by interacting with the bacterial ribosomes in different ways?

Answer 30

1. Tetracyclines - prevent the attachment of tRNAs carrying amino acids 2. Chloramphenicol - prevents the formation of peptide bonds

Question 31

How can antibiotics be changed if resistance develops?

Answer 31

- they can be changed by targeting different stages of the mRNA translation