DNA and Chromosome Structure Flashcards
Phosphate group - Sugar
- 5 Carbon Sugar
- Either ribose (RNA) or deoxyribose (DNA)
- 2’-OH present = RNA; 2’-OH absent = DNA
Purines - What are the names?
*Pure As Gold
Adenine and Guanine
Pyrimidines - What are the names?
Pyrimidines are CUT from purines
- Cytosine, Uracil, Thymine
- Pyrimidines have only one ring, so they’re “cut”
from the purines which have two rings
What is the difference between
a nucleotide and a nucleoside?
A nucleoside does not have a phosphate group where a nucleotide has a phosphate group.
Who discovered the ratios of the four
bases of DNA in organisms? What are
these ratios?
Erwin Chargaff
Chargaff’s ratio is A=T and G=C
Who proposed the current model of DNA
structure?
Watson and Crick proposed the current double helix
model of DNA. Their model has the sugar and
phosphate on the outside and the nitrogenous bases
on the inside.
How do you determine the 5’ and 3’ ends of a strand?
5’ carbon has a free phosphate group, 3’ carbon has a
free hydroxyl group (OH).
How do you determine whether or not a chemical model is
RNA or DNA?
If the 2’ carbon has an H its DNA, if it has
an OH it is RNA
Minor Groove
The outside of the DNA strand
Major Groove
The inside of the DNA strand
Exam Question: If a DNA strand contains contains 35% Cytosine, what percentage of bases do you expect to be Thymine?
You would expect there to be 15% Thymine. Chargaff
found that A=T and G=C. If 70% of the DNA is made up of
G and C pairings that means the remaining 30% must be
made from A and T pairings. 30/2=15.
Exam Question: You are investigating two sequences of DNA: one is made up of a majority C/G nucleotide pairs, and one is majority A/T pairs. Which strand would require a higher temperature to denature? Explain your reasoning.
The strand with high GC content would require a higher temperature to denature while the strand with high AT content would require a lower temperature to denature. This is because heat can cause paired strands to unzip due to the strength of the hydrogen bonds. Since GC pairings have 3 hydrogen bonds compared to the two in AT
pairings it would require more heat to sever the bond.
DNA Structure: Primary
Nucleotide Sequence
DNA Structure: Secondary
Double Helix
Nucleotide Sequence Variation
- SNPs
- INDELS
Double Helix Forms
A form, B form, C form
Most Common Double Helix Form?
B Form, Right Handed
DNA Structure: Tertiary
higher level organization of the double helix
Examples of Tertiary Structure
Supercoiling, nucleosomes, heterochromatin, euchromatin
Nucleic Acids can pair to themselves if what occurs?
Palindromic motifs
Only possible if sequence is complementary with:
The same strand
5 types of histones. DNA is wrapped around a set of ___ histones
8
Which histone acts as a clamp to secure the coil?
H1
DNA has a _________ charge and histones have a _______ charge.
Negative, Positive
Acetyl groups have _______ charge.
Negative
What does histone acetylation do…
…In the histone?
…In the chromatin conformation?
Makes histones neutral
Makes nucleosomes spread out
What proteins does
chromatin consist of?
Histones, Scaffold
proteins
What role do topoisomerases play in supercoiling?
Topoisomerases break and twist DNA to add or relieve supercoiling;
prokaryotes and eukaryotes use different topoisomerases.
What role do scaffold proteins play in supercoiling?
Scaffold proteins anchor supercoils (in eukaryotes only).
What kinds of bonds do topoisomerases break and make?
Phosphodiester bonds
Telomeres are made up of __________
STRs
What is the function of the protein shelterin?
Protects the telomere by making sure the cell doesn’t
see the telomere as a broken chromosome that needs
to be repaired
What important function do telomeres serve?
Protecting loss of coding regions (genes) on the lagging
strand during replication. When the chromosome
shortens after replication, STRs in the chromosome
telomeres are lost rather than genetic material
Telomeres form ____ and ______ loops.
T, D
