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Summary CHAPTER 4 DNA, CHROMOSOMES AND GENOMES
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summary and notes of the lecture given in Groningen (Rijksuniversiteit)
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CHAPTER 4 DNA, CHROMOSOMES AND GENOMESThe chemistry of cells is dominated by macromolecules with remarkable properties
Antonie van Leeuwenhoek’s observation: he could divide cells.
350 years ago.
Introduction
In the past people were convinced that chromosomes composed proteins.
In Second World War they doubted whether it was true or not.
Experiment (investigated pathogenic bacteria)
They have a rough and smooth phenotype. The smooth phenotype (red) were
pathogenic, rough (yellow) are not pathogenic anymore. He was using the pathogenic
materials and adding that to the yellow bacteria and could find some bacteria became
again the red bacteria.
He separated DNS, RNA, protein etc. Only the fraction of DNA can covert to pathogenic
bacteria. So DNA is the molecule that carries the heritable information.
A DNA molecule consists of two complementary chains of nucleotides.
- G-C(3 hydrogen bonds)
- A-T(2 hydrogen bonds)
- Purines: base met 2 ringen: A, G
- Pyrimidine: base met 1 ring: C, U, T
In DNA the side chains are pointed inside. This fits because one nucleotide is small and
the other is larger. A and G large. C and T small.
5’-end is the position of the phosphate.
3’-end is the position of the hydroxyl group attached to the ribose.
Base paring is only possible if the helix is anti-parallel.
The more hydrogen bonds, the stronger the affinity. The more G≡C content, the higher
the ‘melting point’. More energy is needed to break the bonds.
Major groove; more spacious, more wide, DNA regulating proteins prefer the major
groove, more space and chemistry.
Minor groove
The structure of DNA provides a mechanism for heredity
Two different strands, sequence
different but they are complementary.
That is the S and S’-strand. This causes
the copy being identical. Start reading
the DNA-sequence from 5’ end. Copying
DNA also takes place in that order.
, Genes can be complementary different strands. The genes can be either on either side of
the strands, but will always be read from 5’ to 3’.
Eukaryotes have split genes. You’ve got introns in between, they are not coding. The
yellow ones are extrons and are coding for protein.
Splicing
In eukaryotes, DNA is enclosed in a cell nucleus
- Smaller dark fragments, genetically inactive: heterochromatin
- Not dark fragment: euchromatin
- rRNA is transcripted in the nucleus.
- Nuclear lamina: mash work
- Pores: RNA is going out the nucleus via the pores.
- Microtubule: become active during cell division. Microtubule will be contracted
and later separated in two. Each one goes to a daughter cell.
Eukaryotic DNA is packaged into a set of chromosomes. Chromosomes contain
long strings of genes.
- Chromosome 1 is the largest.
- Chromosome 22 is the smallest.
- 2 X for females.
- 1 X and 1 Y for men.
- DNA hybridization: short strand of nucleic acid tagged with a fluorescent dye
serves as a “probe” that picks out its complementary DNA, lighting up the target
chromosome at any site where it binds. (mitosis)
- Giemca staining: chromosome colouring in a way of looking at the karyotype of
a person
Red pins -> indicating genes that code the rRNA.
Karyotype display of human chromosomes at mitosis
Chromosomes contain long strings of genes
- A lot of DNA in eukaryotic cells does not encode for a gene. Some of this DNA is
crucial for the control of gene expression
- Human DNA are less densely packed
The nucleotide sequence of the human genome shows how our genes are
arranged.
- DNA is not very efficient. There are a lot of introns. Maybe the noncoding part has
a stabilization function or a regulatory function.
- Junk-DNA: regions of DNA that are noncoding.
- People proven that if you’ve got leukaemia, the 9 part is longer, a part of 22 has
been transferred to 9. A part of 22 is deleted. This happens when they form white
blood cells. A gene in chromosome 22 and a gene in chromosome pair 9 are being
fused together. Transcription and translation are different and form another kind
of protein.
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