Unfamiliar material Flashcards
Cell theory
- All living creature are made of cells
- Cells are basic structural units of all organisms.
- Cells originate from pre-existing cells through cell division.
- Energy flows occurs within cell.
- Hereditary information is passed on from cell to cell.
- All cells have the same basic chemical groups
G1:
Produce cytoplasm, proteins & organelles
* Cells increase in size
G2:
Cell continues to grow & prepare for division.
Cells that stay in G0 phase: (do not divide:
Heart cells, muscle cells, neurons, red blood cells.
Where is Microtubule organizing center: centrosome?
Eukaryotes only.
Not found in plants or fungi.
What are 3 types of microtubules?
- Kinetochore
- Astal
- polar
Kinetochore microtubule
Attach to chromosomes kinetochore.
Produced by mitotic spindle
Astral microtubule
Extend from centrosome to cell membrane.
Spindle apparatus orientation
Push MTOCs to opposite ends.
Polar microtubule
Arise from each MTOCs & connect with each other.
Push MTOCs to opposite ends.
How do.Centrioles look like?
hollow cylinder of 9 triplets of microtubules (9 x 3)
Steps of Animals cytokinesis:
- Beings in late anaphase
- Forms a cleavage furrow
- Myosin motor - travels along actin filament & contracts.
- pulls plasma membrane toward center of cell
- Forms a contractile ring
- Pinches cell in two .
Steps of Plants cytokinesis:
- Beings in telophase.
- Golgi release vesicles - fuse in center of cell & grow outward in membrane.
- creates a cell plate
- Transforms into a middle lamella.
Types of Cell cycle regulation:
- Functional limitation
2. Cell specific regulation
What are the 2 functional limitations?
- Surface to volume ratio
2. Genome to volume ratio
What are 2 possibilities of the surface to volume ratio?
- When volume of cell is too great = cell divides
- When surface area is not large enough = cell limits growth
What are 2 possibilities of the Genomic to volume ratio>
- When the volume of the cell - places demand on cells genome = cell division.
- When the cell is too large relative to the size of genome = Cell will limit growth
What are the 5 cell specific regulations?
- Cyclin-dependent kinases:
- Cell cycle checkpoints:
- Growth factors:
- Density - dependent inhibition
- Anchorage dependence
Cyclin-dependent kinases:
Regulates kinases ~ phosphorylation
Cyclin activates CDK
What are the 3 Cell cycle checkpoints ?
End of G1, End of G2, M checkpoint
End of G1 checkpoint:
Cell growth assessed.
Ex: liver & kidney induced from G0 to G1.
End of G2 checkpoint:
Accuracy of DN replication & mitosis signal (MPF)
M checkpoint:
Chromosomes attached to spindle fibers
Growth factors:
Receptors for growth factors ~ stimulate cell divsion
Density- dependent inhibition
Cells stop dividing - when surrounding cells density reaches a max.
Anchorage dependence
Cells divide - when attached to external surface (neighboring cells)
Nucleotides in DNA are linked by:
phosphodiester bonds
Hydroxyl placed on which carbon on DNA:
3’
Hydroxyl placed on which carbon on RNA:
2’ & 3’
Nucleosome
compacted DNA + histone
Which histone keeps DNA wrapped around the histone core in nucleosome?
H1
Acetylation:
Removes an acetyl group (+) from the DNA (-) –> DNA loosely packed (Euchromatin) = increase transcription
De-acetylation:
Add acetyl groups (+) to the DNA (-) –> DNA tightly packed (heterochromatin) = Decrease transcription
Methylation:
Add methyl can up regulate or down regulation depending on which AA receives methyl group.
Replication fork
creates tension
Topoisomerase (DNA gyrase ~ in bacteria)
relieves tension = creates small nicks
Primase:
places RNA primer at origin of replication.
- Provides 3’ hydroxyl for DNA)
DNA polymerase extends in which direction?
5’-3’
DNA polymerase reads template in which direction?
3’-5’
Telomerase:
enzyme extends telomeres.
Transcription in prokaryotes:
initiation
elongation
Termination
Initiation in prokaryotes: (1 step)
- RNA polymerase binds to promoter sequence.
Promoter
helps to attract RNA polymerase
Elongation in prokaryotes: (2 steps)
Begins after transcription bubble is established (A & T rich)
- RNA polymerase travels along template (non-coding or antisense) -> 3’-5’ direction
- RNA extends in 5’-3’ directions
Termination in prokaryotes:
- RNA polymerase transcribes terminator sequence.
Where does transcription occur in prokaryotes?
Cytosol
RNA holoenzyme
RNA polymerase + sigma factor
How many types of termination do prokaryotes have?
Rho independent termination and Rho dependent termination
Rho independent termination:
- Terminator sequence of DNA causes RNA transcript to fold into a hairpin loop.
- Hairpin loop: causes RNA polymerase to pause after a certain amount of time.
- In the pause: DNA adenine transcribed into Uracil.
- Those weak bonds between adenine and uracil cause instability - RNA polymerase falls off & transcript is released.
Rho dependent termination:
- Rho binds to protein Rho binding site of RNA transcript. 2. Rho moves along RNA transcript in 5’-3’ direction, same direction as the extension of RNA polymerase.
- Rho will catch up to RNA polymerase b/c of transcription stop point - forcing RNA to pause.
- Rho will displace the RNA transcript and transcription ends.
What is an operon?
a group of related genes. ~ has one promoter site.
Lac operon:
Inducible operon
Lac I ?
lac repressor protein
Constitutively expressed.
Presence of lactose?
- allolactose binds to lac repressor ~ undergoes conformation change.
- RNA polymerase binds to the operator region.
Function of CAP and CAMP?
increase level transcription. CAP binds to CAMP
CAMP inversely related to
Glucose
What is operator region?
sequence of DNA that lies near promoter site, regulatory region of operon.
Tryptophan operon:
Repressible operon (always active)
If tryp levels are HIGH:
Tryp binds to the repressor ~ activating it .
Repressor binds to the operator site ~ prevent transcription
If tryp levels are LOW:
Tryp repressor is inactive ~ cant bind to the operator region
Transcription occurs.
How many domains does attenuation have?
4 domains
Domain 1:
contains codons for the amino acid tryptophan
Domain 4:
Attenuation sequence
High Tryp: What happens at Domain 3 & 4
RNA transcription will attach ~ forming the hairpin loop
Termination of sequence
Low Tryp: What happens at domain 1?
Ribosome will pause at domain 1 of RNA transcript