Post on 13-Dec-2015
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Molecular biology• Though all aspects of biology can be studied at the
molecular level, molecular biology is usually restricted to the molecules of genes/gene products/heredity – molecular genetics
• Experiments in molecular biology are done using model organisms
• Two classes of organism• Prokaryotes• Eukaryotes
Prokaryotes vs. Eukaryotes
bacteria• 1 bacteria = 1 cell• lower organisms • Escherichia coli (E. coli)
• plasma membrane• nucleus• organelles
Cells in eukaryotes• body (somatic) cells
• differentiated into special cell types (brain cells, liver cells …)• produce by simple cell division – mitosis
• sex cells (gametes)• egg, sperm• used for sexual reproduction (only eukaryotes)• meiosis – reduction of the amount of genetic material
Eukaryotic chromosomes• Threadlike DNA, carries genes• Each organism has specific number of chromosomes• Sex chromosomes (determine gender – XX (female), XY
(male)), autosomal chromosomes• 46 in human, 2 sex, 44 autosomal• Come in pairs (two in pair have the same shape and
same set of genes (but different alleles)), homologs, diploid
Mitosis
2c
4c
2c 2c
diploid (2n) mother cell
identical diploid (2n) daughter cells
division
DNA synthesis
Sexual reproduction• Egg gets fertilized by sperm. Zygote is cretaed.• Zygote is diploid (divides by mitosis), thus the gametes
must be haploid!• In organism with diploid
cells, how do you get haploid?
• Meiosis (another type of cell division)
Meiosis• The result of meiosis is haploid cell.• From one parent diploid cell you get four cells haploid. In
addition, homologous chromosomes go through recombination.
http://www.britannica.com
DNA• Every living thing on Earth.• Biomacromolecule
• Consists of repeating units
• DNA in organism does not usually exist in one piece• chromosomes
Deconstructing DNA• http://www.umass.edu/molvis/tutorials/dna/• bases, deoxyribose sugar, phosphate – nucleotide• Bases are flat → stacking• pYrimidines – C, T• puRines – A, G
Nucleotide• nucleosides are interconnected by phospohodiester bond• nucleotide monophosphate
nucleoside
Biological role of different DNAs• B-DNA
• canonical DNA• predominant
• A-DNA• Conditions of lower humidity, common in crystallographic
experiments. However, they’re artificial.• In vivo – local conformations induced e.g. by interaction with
proteins.
• Z-DNA• No definite biological significance found up to now.• It is commonly believed to provide torsional strain relief
(supercoiling) while DNA transcription occurs. • The potential to form a Z-DNA structure also correlates with
regions of active transcription.
Different sets of DNA• nuclear DNA
• cell’s nucleus• majority of functions cell carries out• sequencing the genome – scientists mean nuclear DNA
• mitochondrial DNA• mtDNA• circular, in human very short (17 kbp) with 37 genes (controling
cellular metabolism)• all mtDNA comes from mom
• chloroplast DNA• cpDNA• circular and fairly large (120 – 160 kbp), with only 120 genes• inheritance is either maternal, or paternal
Structure of DNA in the eukaryotic cell
• DNA in human chromosomes: 3.2 109 bp. As we’re diploid: 6.4 109 bp.
• 0.33 nm per bp 2.1 m in each nucleus, size of the nucleus: 5-10 m across
• DNA is highly compacted. Combination DNA + proteins.• During interphase, when cells are not dividing, the genetic
material exists as a nucleoprotein complex called chromatin, which is dispersed through much of the nucleus.
• Further folding and compaction of chromatin during mitosis produces the visible metaphase chromosomes.
• euchromatin – extended• heterochromatin – condensed