Chapter 4: Structure and Function of DNApost.queensu.ca/~biol330/4_DNA.pdf · DNA and genomes. Long...
Transcript of Chapter 4: Structure and Function of DNApost.queensu.ca/~biol330/4_DNA.pdf · DNA and genomes. Long...
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Chapter 4: Structure and Function of DNA
Overview:Nucleic acid chemical compositionChromosome three dimensional structure
Goals:Understand how genes are physically organized
within cellsUnderstand the links between DNA structure and
regulation of DNA replication and transcription
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DNA structureNitrogenous bases:
purines: adenine, guanine
pyrimidines: thymine, cytosine, uracil
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DNA structureNucleosides are nitrogenous base
+ a sugar (deoxyribose or ribose)CH3
1
23
4
5
OHOH
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Examples: adenosine & deoxyadenosine,
guanosine, thymidine, cytidine
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DNA structureNucleotides are nucleosides esterified to one or more phosphates (e.g. adenosine triphosphate-ATP
or deoxyadenosine triphosphate -dATP)
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DNA structureDNA is a polymerized chain of nucleotides
Pyrophosphate(PPi)
+
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DNA structureStrands have a 5’ end (phosphate) and a 3’ end (sugar)
5’ end(5-prime)
3’ end(3-prime)
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DNA structure
2 DNA strands anneal (hybridize): specific, complementary base pairs form hydrogen bonds to make double stranded DNA
A
T
C
G
T
A
G
C
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DNA structureDNA strands are anti-parallel
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DNA and genomesLong stretches of DNA make chromosomes
The collection of chromosomes within the cell is the genome.
Prokaryotes and organelles have genomes that are:
• single, circular chromosomes• no histones• functionally related genes are regulated
together as operons
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Eukaryote genomesEukaryote (nuclear) genomes are:• variable number of chromosomes• histones present• single genes• enclosed in a nucleus
How do you pack 40km of DNA into a 6um2
nucleus?
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Chromatin is double stranded DNA, with the associated proteins
Chromatin structure allows long strands of DNA to be condensed into ordered, accessible arrangements
Chromosome structure
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Chromosome StructureChromosomes are
coated with histone and non-histone proteins
Histone octamers organize chromosomes into nucleosomes
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Chromosome Structure
Non-histone proteins bind other places on chromosome
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Chromosome Structure
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Histones also regulate nuclear activity: changes in structure can alter gene expression:
•acetylation•phosphorylation •methylation
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Chromosome numberDNA of a genome
is divided into chromosomes (variable size and number)
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Chromosome structureGenes include:• Exons-coding regions• Introns- non-coding regions interspersed
between exons• Regulatory sequences
In addition to genes, chromosomes have lots of “non-coding” sequence
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Chromosome structureStructural features:• Replication origin• Centromere• Telomeres
Repetitious DNA• LINES and SINES• DNA only transposons• Segmental duplications and simple sequence
repeats
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Chromosome structure