[2.1] structure of DNA and RNA

Question 1

what similarities and differences do all nucleotides share?

Answer 1

• they all have the same generalised structure (phosphate, deoxyribose sugar, base)
• the thing that makes them different is the base

Question 2

what are the bases?

Answer 2

adenine
guanine
cytosine
thymine

Question 3

how do the bases bind?

Answer 3

• adenine and guanine are purines
• cytosine and thymine are pyrimidines
• purines always bind with pyrimidines

A = T (double hydrogen bond)
G ≡ C (triple hydrogen bond)

Question 4

what shape does DNA form?

Answer 4

a double helix

Question 5

what is a phosphodiester bond?

Answer 5

the bond that is formed when the OH group on the 3rd carbon of a deoxyribose sugar binds to the phosphate group on another nucleotide during a condensation reaction

Question 6

how are the DNA strands in a double helix arranged?

Answer 6

they run antiparallel to each other (ie. upside down)

Question 7

where is the DNA found within the nucleus?

Answer 7

1. double helix structure is formed
2. DNA wraps around histome protein (only in eukaryote)
3. histomes coil to form chromosomes, which are found in the nucleus
4. however, during most of the cell cycle, DNA in the nucleus is unravelled and known as chromatin

Question 8

what are the differences between prokaryotic and eukaryotic DNA [4]?

Answer 8

• histome proteins only found in eukaryotic DNA
• e DNA is linear whereas p DNA is circular
• e DNA is contained in the nucleus whereas p DNA is free-floating within the cell
• e DNA has introns (interrupting regions in the gene which do not code for the sequence of amino acids) whereas p DNA does not have introns

Question 9

what are 4 differences between RNA and DNA?

Answer 9

• RNA has a ribose sugar, DNA has a deoxyribose sugar
• in DNA adenine binds to thymine, in RNA uracil binds to thymine
• in RNA bases can be paired or unpaired, in DNA they can only be paired
• RNA is shorter than DNA

Question 10

what is the function of RNA?

Answer 10

to be involved in the process of protein synthesis

Question 11

what is mRNA (messenger) and what is its role?

Answer 11

• it is an exact copy of the sense strand of DNA
• a single strand of mRNA which has unpaired bases and can be variable length depending on the length of the gene it is from
• it heads out of the nucleus and to the ribosome to be read

Question 12

what is tRNA (transfer) and what is its role?

Answer 12

it goes out into the cytoplasm and finds a particular amino acid and then binds onto that amino acid and brings the amino acid to the ribosome to be added to a growing polypeptide chain during protein synthesis

• fixed length
• there is an anticodon complementary to a codon
• there are paired bases due to folding on the molecule

Question 13

what is rRNA (ribosomal) and what is its role?

Answer 13

it allows ribosomes to interact with the mRNA to help in the process of protein synthesis

• found in ribosomes
• fixed length
• unpaired bases