Unit 3 - DNA organization in Eukaryotes and Prokaryotes Flashcards
(28 cards)
Nucleosome
a unit of DNA storage consisting of 8 histones with DNA strands wrapped around them; the DNA around each nucleosome is about 147 nucleotides long
(r further packaged into solenoids)
Linkers
stretches of DNA connect one nucleosome to the next. At this level of organization, the strand of chromatin appear like a string of beads
Solenoid
a group of 6 nucleosomes (30nm chromatin fibers)
Prokaryotic DNA organization
have simple DNA structures
- DNA exists on one primary, often circular, chromosome
- DNA is less tightly bound and more easily accessed by the enzymes and other mols involved in replication
Plasmids
r smaller, circular sections of DNA that float throughout cells
- exist in addition to the main chromosome
- can exist in one cell and enter the next
Conjugation
- a plasmid can exit one cell and enter another
- plasmid of one bacterium can move into another bacterium and join its genome
Phenomena allows 2 things
- a natural variation of bacteria
- researches to insert specific genes into host bacteria
Prokaryotes don’t have proteins to help package DNA like Eukaryotes
- unbound by a nuclear membrane and DNA is less tightly bound and more easily accessible by the enzyme and other mol involved in replication
Supercoiling
used to protect DNA; continuos twisting of prokaryotic DNA to reduce size
Telomeres; DNA loss during replication - DNA polymerase and Oki frags
1) DNA polymerase produces small fragments of DNA (OF) on a lagging stand
2) OF are initially attached to RNA primer
Telomeres; DNA loss during replication - problem w OF
the lase OF begins at the last RNA primer position which is located close to but not at the end of the strand
Telomeres; DNA loss during replication - problem RNA primers
RNA primers is removed, but since DNA polymerase can not bind to the 5’ end, it leaves that section of DNA uncopied
Telomeres; DNA loss during replication - result
DNA is shorter by the amt of uncopied segments
Loss of DNA during each cycle or replication problem
causes chromosomes to constantly get shorter and can lead to the loss or damage of important genes
Solution to loss of DNA during each cycle
1) to prevent the loss of essential coding regions, non-coding sequences r found at the end of chromosomes know as telomers
Telomeres
every time a DNA replication part of the telomeres r lost but the coding regions of DNA r kept intact
Telomeres act like caps at the end of chromosomes
protect the DNA from losing valuable coding information during replication
other functions of DNA replication and aging (4)
1) help prevent chromosome ends from fusing to other
2) prevent DNA degradation from enzymes called nuclease
3) assists DNA repair
4) many play a role in determining the number of times a cell divides and play a really important role in determining lifespan of an organism
Role of Telomeres During Replication
repeating sequence of nucleotides at the end of DNA
Base pair code sequence found at end of Human DNA
5’ - TTAGGG - 3’
- repeating 2000 times
- 100 bp lost per replication
Cell Senescene
- essential portions of DNA may be lost during subsequent replication
- cells can lose ability to function properly
- may lose ability to grow / metabolize / or divide
Biological Clock
telomeres r like a BC because they r counting down the total number of times that a cell can divide; know as the HAYFLICK Limit
Hayflick Limit
(total number of times that a normal cell can divide)
- diff in each species
- in humans, cells can divide about 50x
- The length of telomers is not related to how long an individual of the species live.
Germ Line Cells
MUST maintain their genetic integrity from parent of offspring (Cannot afford to lose any genetic information)
