Dna Shit Flashcards
(12 cards)
Watson and Crick’s model of replication
- complimentary base pairing allows parental strands to act as templates for DNA replication of new strands
-parental strands can unwind by breaking the hydrogen bonds between bases
-semi conservative replication where the double helix will contain a parental strands can unwind and a newly synthesized strand
How is DNA organized in eukaryotes ?
-Humans DNA has 3.2 billion base pairs (3200Mb or 3.2Gb ) 2 meters packed in a cell 250000 times smaller than
-Eukaryotes have multiple, linear DNA molecules enclosed in a nucleus
-T keep the DNA organized and help regulate gene expression , it is condensed into CHROMATIN
-The DNA double helix is first wrapped twice(ish) around his tongue proteins to form a nucleosome
-Each DNA molecule is a repeating series of nucleosomes called 10nm chromatin fibres, that looks like “beads on a string” under an electron microscope
-Additional histones cause the chromatin to coil further into 30 nm chromatin fibres (solenoids)
-chromatin is the normal state of our DNA molecules
- it unwinds during DNA replication and transcription
-it condenses further - into chromosomes - during mitosis/meiosis
Histones and DNA packing
There’s a slide with the whole diagram
What are Histones?
Histones are basic, positively charged proteins
- The nucleosome is a histones or tamer (2(H2A, H2B, H3, H4)) with approximately 147bp of DNA rapped around it (1.65X around of octamer)
-Histones H1 binds linker DNA and to nucleosomes to form the 30nm chromatin fibre
If we want to turn our chromatin into chromosome
We need more proteins and more compacting at DNA where its going to hold the highly condensed DNA form, that kind of form cannot be accessed by enzymes, all its really good for is separating those molecules. We call the molecules chromosomes even tho they are not in chromosome form, its because that’s how we discovered them .
Karyotype
Wtf he talks too fucking fast
Euromatin and heterochromatin
-DNA packing/compaction along the chromosome is not uniform
- Euchromatin regions have lower DNA compaction and genes are actively expressed
-Heterochromatin are chromosomal regions of high DNA compaction where gene expression is silenced
-Constitutive heterochromatin: DNA always highly compacted (centromeres and subtelomit regions)
-Facultative heterochromatin: can switch to euchromatin depending on cell type and during development
Reasons for DNA organized as chromosomes
- Chromosomes compact DNA so that it can fit into the cell/nucleus
2.chromosomal structure protects DNA from damage (naked DNA is very unstable) - Chromosomes can be easily separated and transmitted to each daughter cell during cell division
Essential components of eukaryotic chromosomes
-chromosomes need to be fully duplicated (DNA replication) and properly transmitted to each daughter cell during mitosis/meiosis
1.Origins of replication : multiple dna sequences along chromosome which initiate DNA replication
2. Centromere: DNA sequences required for correct segregation of chromosomes by directing formation of the kinetic horse in which mitosis spindle attaches
3. Telomeres: DNA sequences located.at the ends of chromosome that prevent degradation and allow proper replication of the chromosomal ends
What happens to segregation if the chromosome did not have centromere or if they had 2 centromeres?
Chromosomal policy of eukaryotes
-Haploid set of human chromosomes and their number of genes (Ensemble Genome Browser )
“Check pic of diploid set of human female)
-Majority of eukaryotic cells are diploid (2 copies of each homologous chromosome)
-only sexually-reproductive cells (sperm and eggs) have a haploid genome
-some eukaryotes are polyploid (more than a pair of each chromosome ) such as large protists (Tetrahymena: 10-10000 copies ) and flowering plants
How is DNA organized in prokaryotes?
- Prokaryotes typically have a single, circular DNA molecule found in cyto nucleus
-prokaryotic DNA doesn’t need the same r level of compaction as eukaryotic DNA
- They use histones-like proteins (HLPs), also called nucleoid- associated proteins (NAPs)
-rokrayotes also have other small independent circular DNA molecules called plasmids
-Each cell can have multiple different plasmids as well as multiple copies of each plasmid
-Plasmids only carry a few genes - none essential for life
-They carry “bonus ” genes that give them an advantage in some environments
