Nucleic Acids Flashcards
What are the four types of biomolecule?
Carbohydrates
Lipids
Protein
Nucleic acids
What are phospholipids composed of?
A hydrophilic head and hydrophobic tail
What are the hydrophobic tails composed of in phospholipids?
Fatty acids bonded to glycerol
What are the hydrophilic heads composed of in phospholipids?
A phosphate group + glycerol + choline
Examples of nucleic acid?
Deoxyribonucleic acid
Ribonucleic acid
What are the structure of nucleic acids?
A phosphate group
Pentose sugar
Nitrogenous base
What do ALL nucleic acids contain?
A phosphate group
How many carbons does a pentose sugar contain?
5 carbons
What sugars are ribose and deoxyribose?
Pentose sugars (5 carbon sugars)
How do deoxyribose and ribose differ?
Deoxyribose has no oxygen atom at carbon 2, whereas ribose does have an oxygen atom at carbon 2.
Nucelic acids are made up of which monomer?
nucleotides
How many nucleotides
are there?
There are five nucleotides
What are the two groups of nucleotides?
Purines and pyrimidines
what are Purines?
Nitrogenous bases with two carbon rings
WHat are pyrimidines?
Nitrogenous bases with one carbon ring
What does a phosphate group, nitrogenous base, and pentose sugar make up?
A monomer called a nucleotide.
WHat does a nitrogenous base, and pentose sugar make up when the phosphate group is missing?
A nucleoside (only when the phosphate group is missing)
What is a monomer?
a smaller and repeating unit or molecule from which a larger molecule is made (polymer)
Define polymer.
Large molecules which are made up of many monomers in a chain.
When and who discovered the double helix structure of DNA?
James watson and francis crick discovered it in 1953.
Which scientists aided in the discovery of the double helical structure of dna?
Linus Pauling
Rosalind Franklin
Erwin Chargaff
What did Linus Pauling postulate?
Postulated that regions of protein can fold in into a secondary structure known as alpha helix, in the early 1950s.
Developed the ball and stick models
WHat did Rosalind Franklin do?
Studied wet fibers of dna using x ray diffraction
What did the patterns obtained by rosalind franklin indicate?
Indicated several structural features of DNA:
-Helical structure
- More than 1 strand
- 10 base pairs per complete turn
What was Erwin Chargaffs experiment?
Measured the isolation, purification, and measurement of nucleic acids from living cells using many biochemical techniques.
By this time it was already known that DNA contained a, c, g, and t
What is chargaffs rule?
Relative proportions of base pairs suggested complementary base pairing.
% adenine = % thymine
% cytosine = % guanine
This concept became known as chargaffs rule.
What did Watson and Crick do?
Built ball and stick models to draw together all the recent discoverys and observations.
They tried to answer the questons how the two (or more) strands interacted, and an early hypothesis for this was that the strand interacts through phosphate-Mg++ crosslinks
Was the hypothesis by watson and crick correct or not?
Model building showed that this was incorrect.
WHat was the second hypothesis by watson and crick?
Then built models with the
Sugar-phosphate backbone on the outside
Bases projecting toward each other
Bases form H bonds with identical bases in the opposite strand
ie., A - A, T - T, C - C, and G - G
Model building revealed that this also was incorrect
What was the third model/hjypotheiss by watson and crick?
Built ball-and-stick models with A - T and C - G pairing
These were consistent with all known data about DNA structure
In what direction is dna synthesised?
in the 5’ to 3’ direction
What is DNA?
DNA is a polymer of nucleotides with a sugar phosphate backbone. The order of its nucleotides is known as the DNA sequence and runs in the 5’ to 3’ direction. DNA is double stranded and these strands are antiparallel to eachother
In dna, C pairs with…
G
In dna, A pairs with
T
How many hydrogen bonds do A-T bonds have?
2
How many hydrogen bonds do C-G bonds have?
3
Are h bonds strong or weak?
H bonds are relatively weak
WHy are G - C rich regions more stable?
G - C rich regions are more stable than A - T rich regions since they have more hydrogen bonds.
How are the two strands twisted together?
Two strands are twisted together around a common axis
There are 10 bases per complete twist
In what direction does dna turn?
The helix is right-handed
It spirals away from you, moving in a clockwise direction
This is called the B form of DNA
There are two asymmetrical grooves on the outside of this right handed helix known as…
- Major groove
- Minor groove
WHat binds within the grooves on dna?
Certain proteins can bind within these grooves and interact with a particular sequence of bases
What form of dna is most commonly found in living cells?
B-DNA.
Where can A-DNA and Z-DNA form?
However, under certain in vitro conditions, A-DNA and Z-DNA double helices can also form.
What is A-DNA?
Right-handed helix
11 bp per turn
Occurs under conditions of low humidity
Little evidence to suggest that it is biologically important
What is Z-DNA?
Left-handed helix
12 bp per turn
Its formation is favored by
GC-rich sequences, at high salt concentrations
Cytosine methylation, at low salt concentrations
Evidence from yeast suggests that it may play a role in transcription and recombination
DNA Packaging in Eukaryotes:
Human nuclear DNA is around 2m in length
To fit within a living cell DNA must be extensively compacted
Aided by DNA-binding proteins (such as histones)
How are the nitrogenous bases different in RNA?
Uracil is present instead of thymine.
A binds with U instead of T
How many nuceliotides in length is rna?
several hundred to several thousand nucleotides in length
How many strands rna got?
1.
SIngle stranded.
Describe the secondary structure of rna?
Different types of RNA secondary structures are common
Short double-stranded regions can form due to complementary base pairing within one RNA strand
What are the different types of RNA?
rRNA (ribosomal)
tRNA (transfer)
mRNA (messenger)
siRNA* (si RNA) and others
What is siRNA?
Small (or short) interfering RNA (siRNA) is the most commonly used RNA interference
(RNAi) tool for inducing short-term silencing of protein coding genes. siRNAis a
synthetic RNA duplex designed to specifically target a particular mRNA for degradation.
