8.3 - The structure of ribonucleic acid

Question 1

how is the coded information on the DNA in the nucleus transferred to the cytoplasm where it is translated into proteins?

Answer 1

Sections of the DNA code are transcribed onto a single-stranded molecule called ribonucleic acid (RNA)
—> the RNA that does this is messenger RNA (mRNA)

Question 2

What makes the mRNA good at its job

Answer 2

• small enough to leave the nucleus through the nuclear pores and to enter the cytoplasm
• where the coded information that it contains is used to determine the sequence of amino acids in the proteins which are synthesised there

Question 3

What does the term codon mean

Answer 3

Refers to the sequence of 3 bases on mRNA that codes for a single amino acid

Question 4

What is the Genome

Answer 4

The complete set of genes in a cell, including those in mitochondria and/or chloroplasts

Question 5

What is the proteome

Answer 5

• the full range of proteins produced by the genome
• this is sometimes called the complete proteome, in which case the term proteome refers to the proteins produced by a given type of cell under a certain set of conditions

Question 6

Describe the structure of RNA

Answer 6

• forms a single strand in which each nucleotide is made up of the following:

Question 7

What are the 2 types of RNA that are important in protein synthesis

Answer 7

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

Question 8

Describe the structure of mRNA

Answer 8

• long strand arranged into a single helix
• the base sequence of mRNA is determined by the sequence of bases on a length of DNA in a process called transcription
• once formed, mRNA leaves the nucleus via pores in the nuclear envelope and enters the cytoplasm, where it associates with the ribosomes, and act as a template for protein synthesis
• structure is suited for its function because: it possesses information in the form of codons (3 bases that are complementary to a triplet in DNA). — the sequences of codons determines the amino acid sequence of a specific polypeptide that will be made

Question 9

Describe the structure of transfer RNA (tRNA)

Answer 9

• relatively small molecule made up of around 80 nucleotides
• single-stranded chain folded into a clover-leaf shape, with 1 end of the chain extending beyond the other
  —> this is the part of the tRNA molecule to which an amino acid can easily attach
• at opposite end, a sequence of 3 other organic bases, known as the anticodon
• given that the genetic code is degenerate there must be as many tRNA molecules as there are coding triplets. However, each tRNA is specific to one amino acid and has an anticodon that is specific to that amino acid

Question 10

Draw the clover-leaf structure of tRNA

Answer 10

Question 11

What do mRNA and tRNA do during protein synthesis

Answer 11

• an anticodon pairs with the 3 complementary organic bases that make up the codon on the mRNA
• the tRNA structure (with its end chain for attaching amino acids and it anticodon for complementary organic pairing with the codon of the mRNA) is structurally suited to its role of lining up amino acids on the mRNA templates during protein synthesis

Question 12

Compare the differences in terms of chains: between DNA, mRNA, tRNA

Answer 12

• DNA = double polynucleotide chain
• mRNA = single polynucleotide chain
• tRNA = single polynucleotide chain

Question 13

Compare the differences in terms of molecule size: between DNA, mRNA, tRNA

Answer 13

• DNA = largest
• mRNA = smaller than DNA, but larger than tRNA
• tRNA = smallest

Question 14

Compare the differences in terms of shape: between DNA, mRNA, tRNA

Answer 14

• DNA = double-helix molecule
• mRNA = single-helix molecule (except in a few viruses)
• tRNA = clover-shaped molecule

Question 15

Compare the differences in terms of pentose sugar: between DNA, mRNA, tRNA

Answer 15

• DNA = deoxyribose sugar
• mRNA = ribose sugar
• tRNA = ribose sugar

Question 16

Compare the differences in terms of organic bases: between DNA, mRNA, tRNA

Answer 16

• DNA = adenine—thymine, guanine—cytosine
• mRNA = adenine—uracil, guanine—cytosine
• tRNA = adenine—uracil, guanine—cytosine

Question 17

Compare the differences in terms of where its found: between DNA, mRNA, tRNA

Answer 17

• DNA = mostly found in nucleus
• mRNA = manufactured in nucleus, but found throughout cell
• tRNA = manufactured in the nucleus but found throughout the cell

Question 18

Compare the differences in terms of quantity from cell to cell: between DNA, mRNA, tRNA

Answer 18

• DNA = constant for all cells of a species (except gametes)
• mRNA = quantity varies cell to cell and with level of metabolic activity
• tRNA = quantity varies cell to cell and with level of metabolic activity

Question 19

Compare the differences in terms of stability: between DNA, mRNA, tRNA

Answer 19

• DNA = chemically very stable
• mRNA = less stable than DNA or tRNA, individual molecules are usually broken down in cells within a few days
• tRNA = chemically more stable than mRNA but less stable than DNA

Question 20

Give the 2 types of molecules from which a ribosome is made

Answer 20

• proteins
• rRNA

Question 21

difference between DNA and mRNA, in terms of strands

Answer 21

• DNA = double stranded
• mRNA = single stranded (therefore no hydrogen bonds or base pairing)

Question 22

Draw the structure of an amino acid

Answer 22