Lecture 1- Nucleic Acids And Chromosome Flashcards
What is the is difference between a nucleoside and nucleotide?
Nucleoside: base + sugar
Nucleotide: base + sugar + phosphate
What is attached to the 1’ and the 5’ of deoxyribose in DNA?
1’ - base
5’ - phosphate
What is the difference between ribose and deoxyribose?
Ribose has a hydroxyl group on 2’ but deoxyribose has a hydrogen attached
Which bases are purines (2 sugar rings) and which are pyramidines (1 ring)?
Purines: Adenine + Guanine
Pyramidine: Cytosine + Thymine + Uracil
What are the differences in structures between adenine and guanine?
6’ - Adenine has amino group but guanine has carbonyl
2’ - Adenine has hydrogen but guanine has amino group
What are the differences in structures between Cytosine, Thymine and Uracil?
4’- C has amino group, T and U have carbonyl groups
5’- Only T has methyl group
Give the names of the corresponding nucleosides to these bases: Adenine Guanine Cytosine Uracil Thymine
Adenosine Guanosine Cytidine Uridine Thymidine
Describe the structure of a single strand of DNA (6 points)
1) Long chain of deoxyribonucleotides
2) Joined together by phosphodiester binds
3) 3’ -OH of sugar of one nucleotide linked to a phosphate group which is attached to a 5’ sugar of following nucleotide.
4) Each deoxyribose is bonded to a nitrogenous base by a B-glycosidic bond
5) Chain has a 5’ and 3’ end so it isn’t symmetrical
6) Conventionally written from 5’ –> 3’ (free phosphate to free -OH)
Explain the structure of the double-stranded helix w.r.t. base-pairing, grooves and directionality.
1) Right-handed double helix
2) Chains are anti-parallel
3) Sugar-phosphate backbone on the outside with negative charges outside
4) A-T= 2 Hydrogen bonds
C-G = 3 Hydrogen bonds
5) Major and minor groove
6) 10bp per helical turn, strand 2nm wide
What are the conditions for melting and re-annealing?
Heat or Low Salt= Melting or Denaturing
Cool or High Salt= Re-anneal or Hybridise
Compare the E. coli and H. sapiens genome.
E.coli:
1) 4.6 x 10^6 base pairs
2) Single circular double stranded DNA
3) DNA is 1.4mm long
H. sapiens:
1) 3 x 10^9 base pairs
2) Linear, double- helical chromosomes
3) Diploid= 46chromosomes, 22 autosomal pairs and 2 sex chromosomes
What is a karyotype?
Profile of someone’s chromosomes
Explain the packaging of DNA into nucleosomes and relate this to DNA structure.
DNA tightly packed into chromatin which is DNA wrapped around histone proteins
2) Lowest level = NUCLEOSOME. DNA packed around histone which causes 7-fold condensing. You get Core and linker DNA.
3) Nucleosome packed into 30nm chromatin FIBER= 40-fold condensation.
4) Chromatin fiber super folded into loops= CHROMOSOMES. 10, 000 fold shorter than original DNA
Describe the structure of nucleosomes.
- 8 histones in the middle: 2 each of 2A, 2B, 3 and 4 and then histone 1 between the nucleosomes.
- Histones: +vely charged proteins which interact with -vely charged sugar-phosphate backbone
- around 150bp per nucleosome
