DNA Structure

Question 1

Pyrimidines

Answer 1

single carbon/nitrogen ring
uracil in RNA only
thymine in DNA only
Cytosine

Question 2

Purines

Answer 2

double carbon/nitrogen ring

Question 3

Nucleoside

Answer 3

Base+ Sugar

Question 4

Nucleotide

Answer 4

Base+sugar+Phosphate

Question 5

DNA

Answer 5

deoxyribonucleic acid
D= deoxyribose (has no O on C2)
N - nucleic acids were so named because they
were first isolated from the nucleus of cells
A – DNA and RNA are negatively charged at physiological
pH and confer the properties of an acid

Question 6

DNA is a polymer of nucleotides, such as:

Answer 6

1. 106–107 nucleotides long
2. Constitutes and encodes our genes
3. Stable: copied and transferred from cell to cell; from
   generation to generation
4. Only found in the nucleus and mitochondria

Question 7

RNA is a polymer of nucleotides, such as:

Answer 7

1. 70-10,000 nucleotides long
2. Mostly involved in protein synthesis
3. Short lived. Three main types: messenger, transfer
   and ribosomal
4. Found in the cytoplasm nucleus and mitochondria

Question 8

Linkage of Nucleotides

Answer 8

• polarity: 5’ phosphate (C5) – 3’ OH (C3)
• phosphodiester bond (covalent)
• catalysed by a polymerase
• forms linear polynucleotide

Question 9

Double-helix structure of DNA was solved by?

Answer 9

Solved by James Watson and Francis Crick in 1953 using X-ray diffraction
images from Rosalind Franklin and Maurice Wilkins.

Question 10

The Structure of DNA

Answer 10

Four key features define DNA structure
• Minor and major grooves
• uniform diameter of 2 nm in its most common B-form
• right-handed twist with 10- 10.5 base pairs per turn
• Antiparallel

Question 11

Complementary Base Pairing

Answer 11

• Nitrogenous bases united by hydrogen bonds
– A purine on one backbone with a pyrimidine on
the other
– A–T two hydrogen bonds
– C–G three hydrogen bonds

Question 12

Law of complementary base pairing

Answer 12

– One strand determines base sequence of other

Question 13

What are the essential functions of DNA?

Answer 13

• Storage of genetic info
• Replication
• Expression
• Mutation

Question 14

What features of DNA are essential to carry out these

functions?

Answer 14

• 4 nucleotides
• Phosphoribose backbone
• Complementarity
• H-bond (weak)
• Nitrogenous bases

Question 15

The double helical structure of DNA is essential to its

functions:

Answer 15

• Storage of an organism’s genetic information; order of
bases.
• Susceptible to change (mutation); change of specific bases.
• It must be precisely copied in the cell division cycle; base
complementarity means that one strand of bases
defines the other.

Question 16

What is the Implications of DNA Structure?

Answer 16

DNA is composed of two complementary strands
Encodes two copies of the genetic information
Each can be used as a template for DNA replication and DNA repair

Question 17

What is Conformation of DNA in Prokaryotes?

Answer 17

Prokaryotic DNA is generally circular, supercoiled and

complexed with an RNAprotein core

Question 18

What are the General Features of RNA Structure?

Answer 18

• 4 bases - A,C,G,U
• Only one nucleotide strand
• Base sequence forms a message
• Much shorter than DNA
– tRNA (transfer), 70 - 90 bases
– mRNA (messenger), variable length often <10 kb (kb = kilo bases)
– microRNAs, 21-25 bases
– rRNAs (ribosomal), several kb
• Migrates to the site of protein synthesis
• Directs protein synthetic machinery
• RNA is transient

Question 19

What are the Major Species of RNA?

Answer 19

mRNA:
tRNA:Transfer ribonucleic acid (tRNA) is a type of RNA molecule that helps decode a messenger RNA (mRNA) sequence into a protein
rRNA:Ribosomal ribonucleic acid (rRNA) is a type of non-coding RNA which is the primary component of ribosomes, essential to all cells. rRNA is a ribozyme which carries out protein synthesis in ribosomes.

Question 20

mRNA:

Answer 20

carries the genetic information copied from DNA in the form of a series of three-base code “words,” each of which specifies a particular amino acid.

Question 21

tRNA

Answer 21

Transfer ribonucleic acid (tRNA) is a type of RNA molecule that helps decode a messenger RNA (mRNA) sequence into a protein

Question 22

rRNA:

Answer 22

Ribosomal ribonucleic acid (rRNA) is a type of non-coding RNA which is the primary component of ribosomes, essential to all cells. rRNA is a ribozyme which carries out protein synthesis in ribosomes.

Question 23

RNAs are generally single-stranded- does it have secondary structure?

Answer 23

….but are rich in secondary structures
Single-stranded RNA can also form many secondary structures in which a single RNA molecule folds over and forms hairpin loops, stabilized by intramolecular hydrogen bonds between complementary bases.