Ch6 Part 3 Flashcards
Endocytosis
Forms an endosome as external material is internalized.
Three types of endocytosis:
1.Phagocytosis
2. Pinocytosis
3. Receptor mediated cytosis
Phagocytosis
nonspecific uptake of large particular matter. Forms a phagocytic vesicle that will merge with a lysosome.
ex. Macrophages in human immune system
Pinocytosis
non-specific uptake of small molecules and ECfluid by invagination
Receptor-mediated endocytosis
Highly specific.
Pits of Clathrin indicate sites of this endocytosis.
Ex. Cholesterol uptake. IF cholesterol remains in blood it forms plaques on walls of arteries –> atherosclerosis
Cell-surface receptors
Three types:
1. Ligand-gated ion channels
2. Catalytic receptors
3. G-protein linked receptor
Ligand-gated ion channels
As you know
Catalytic Receptors
Have enzymatic active site on cytoplasmic side, activated by binding of a ligand to an extracellular portion. Typically the catalytic element is a protein kinase - results in phosphorylation of proteins.
Ex. Insulin receptor
G-protein linked receptor
Transmits signal into the cell via a secondary messenger. Ex. cAMP (note it is the secondary messenger of epinephrine and glucagon so known as “universal hunger signal”
Amplification is a hug component here.
GTP binding is ON switch, GDP is OFF. GTP binds alpha subunit which, as a complex, activates Adenylyl Cyclase resulting in the production of cAMP from ATP –> activates cAMP dependent protein kinase.
Note inhibitory G-proteins inhibit Adenylyl Cyclase, stimulatory, stimulate.
Others do not use cAMP, but activate phospholipase C, which results in an increase in Ca2+ in the cell.
Cytoskeletons
Composed of three different proteins: microtubules (25 nm), intermediate filaments (10 nm), and micro filaments (7 nm)
Microtubules
Hollow protein.
Alpha and beta tubulin polymerized non-covalently.
Dimers of alpha and beta form and then are connected together. Form a sheet. Sheet roles into tube.
Microtubule organizing center (MTOC) is anchor for microtubule, cannot extend from this side. Only grows from one end.
Centrioles
Two within the MTOC.
Each centriole is composed of 9 triplets of microtubules.
centrioles duplicate during mitosis and move to poles. However, Centrioles are non-essential for mitosis.
Aster
Microtubules that extend from centrioles during mitosis.
Polar fibers connect aster to chromosome.
this assembly = mitotic spindle
kinetochore fibers connect kinetochore on chromosome to mitotic spindle.
Cilia and Flagella
Both have a 9+2 microtubule arrangement (9 outside, 2 middle)
Dynein binds individual microtubules together.
Anchored to membrane by basal body. Note: different from prokaryotes.
Microfilaments
Rods formed in cytoplasm from globular protein actin. Two actin monomers wrap around each other to create a filament.
Cause amoeboid movement and pinch cell apart during mitosis.
Intermediate Filaments
Heterogenous (multiple types of polypeptides).
Less dynamic. Appear important in cellular structure. Resisting mechanical stress.
Epithial Cells “upon nipples”
In gut are connected via tight junctions to make impermeable.
In skin are connected via desmosomes.
Heart cells connected by gap junctions.
Tight Junctions
Also known as occluding junctions.
Create seal between cells all the way around. Transmembrane proteins cannot move from apical to basolateral surface when blocked by gap junctions.
Desmosomes
Or Spot Desomosomes
Do not seal, but hold cells together.
Desmosomes are anchored by a plaque of keratin on the intracellular surface.
Anchored by intermediate filaments so do not move throughout the membrane.
Gap junctions
pore-like connections between cells. Polypeptides and organelles cannot pass through.
Interphase
Period of G1 S and G2 leading to mitosis and cytokenesis.
Synthesis - when cell actively replicates genome. By end of S phase, cell has two complete genomes.
Gap phases (G) - I believe cell regulation occurs here.
Prophase
Prophase: formation of densely packed chromosomes. 23 homolgous pairs of chromosomes before formation of two daughter cells. Nuclear envelope becomes many tiny vessicles (known as Prometaphase - quite dramatic).
Nucleolus disappears. spindle and kinetochore fibers disappear. Centrioles move to poles, asters form.
Don’t confuse sister chromatids and homologous pairs.
Metaphase
All chromosomes line up at center and form metaphase plate.
Mitosis stages
Prophase, Metaphase, Anaphase, Telophase (PMAT)
Anaphase
Spindle fibers shorten and centromeres of sister chromatids are pulled away from eachother.
Sounds like cleavage furrow of cytokenesis starts here.
Telophase
Occurs in concert with Cytokenesis.
Telophase i like opposite of prophase. Nuclear membrane forms around two bunches of chromosomes, chromosomes decondense, nucleolus becomes visible.
Oncogenes
Mutated genes that induce cancer.
Genes can be mutations or a result of viral genome
Protooncogenes
Normal genes that under the right (or wrong) circumstances can become oncogenes.
Tumour Suppressor Genes
Code for proteins that either (1) detect damage and halt cell growth until repair is completed
(2) Drive cell death if damage cannot be repaired
p53
Product of tumour suppressor gene.
Will signal for repair, but can also drive apoptosis.
Apoptosis
Can occur as a result of external or internal signals.
Shrinking of cell, disassembly of the cytoskeleton, nuclear envelope breaks down, genome is disassembled. Unique cell-surface proteins emerge that signal phagocytic cells to consume/clear dying cell.
Mediated by caspases - have cysteine and cleave target proteins at aspartic acid sites.
INITIATOR CASPASES - respond to intra or extracellular signals and cluster together which activates them. This leads to the activation of EFFECTOR CASPASES which trigger apoprosis via cleavage of proteins.
