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Chapter 11 Nucleic Acid structure, DNA Replication and…
Chapter 11 Nucleic Acid structure, DNA Replication and chromosome structure
Levels of DNA structure:
Grooves in space-filling model
Major
proteins bind to affect gene expression.
Minor
narrower
`
DNA REPLICATION
Semiconservative Mechanism.
replication produce: DNA molecule with 1 parental and 1 daughter strand
Origin of replication
provide replication bubble that form 2 replication forks (replication proceeds out of them).
Enzymes
DNA helicase: use ATP & travel 5
to 3
to separate strands (moving forks forward).
DNA topoisomerase: travel ahead of forks & relieve additional coiling.
Single-strand binding proteins: coat strands & keep them open.
DNA polymerase: link nucleotides (covalently) + remove RNA primers.
Only work 5
to 3
.
Require: primer to start linking.
Made by: DNA primase from RNA.
DNA ligase: joins adjacent DNA fragments.
Strands:
Leading strand:
DNA synthesized: as long molecule.
single RNA primer.
Lagging strand:
DNA synthesized: as Okazaki fragments.
consist of: RNA primers + DNA.
IN Eukaryotes
Telomers:
no complementary strand at 3
end ( called= 3
overhang).
Problem: DNA polymerase cannot copy tip of 3` end strand
Telomerase enzyme
attach copies of DNA repeat sequence to the end of chromosomes.
Short nucleotides sequences at end of chromosomes.
shortining: is correlated with cellular senescence.
2) Strand= liner polymer strand.
covalent bond (between nucleotides).
Phosphodiester bond (phosphate group link 2 sugars).
phosphate and sugar forms backbone. (bases project away from it).
.
1) Nucleotides= DNA & RNA building blocks.
Composed of:
1) Phosphate group.
attached to 5` carbon on sugar.
Pentose sugar.
(DNA Deoxyribose) (RNA Ribose). Carbons are 1
to 5
clockwise.
Nitrogen base (attach to 1` carbon on sugar).
Purines= same in both Pyrimidines= U in RNA, instead of T in DNA
~10 in each strand per complete turn of helix.
.
DNA compaction levels:
1) DNA wrapping: around histones forming nucleosomes. shortens length 7-fold.
2) 30-nm fiber 3D zigzag of nucleosome. shorten length 7-fold again.
3) Radial loop domain 3nm fibers+ nuclear matrix interact. chromosomes: in discrete territory
3) Double helix= two strands of DNA.
Antiparallel strands: one is 5
to 3
other is 3
to 5
.
.
.
Mechanisms for accuracy:
1) Hydrogen bonds between (A+T) & (G+C)
more stable than mismatched combinations.
If pairs mismatched;
(DNA polymerase):
1) its active site is unlikely to form bonds.
2) can proofread to remove them.
4) Chromosomes= DNA + different proteins (complex structure).
discrete unit of genetic material
5) Genome= complete genetic material in an organism.
Solution:
