Ch6 Part 3

Question 1

Endocytosis

Answer 1

Forms an endosome as external material is internalized.

Three types of endocytosis:
1.Phagocytosis
2. Pinocytosis
3. Receptor mediated cytosis

Question 2

Phagocytosis

Answer 2

nonspecific uptake of large particular matter. Forms a phagocytic vesicle that will merge with a lysosome.

ex. Macrophages in human immune system

Question 3

Pinocytosis

Answer 3

non-specific uptake of small molecules and ECfluid by invagination

Question 4

Receptor-mediated endocytosis

Answer 4

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

Question 5

Cell-surface receptors

Answer 5

Three types:
1. Ligand-gated ion channels
2. Catalytic receptors
3. G-protein linked receptor

Question 6

Ligand-gated ion channels

Answer 6

As you know

Question 7

Catalytic Receptors

Answer 7

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

Question 8

G-protein linked receptor

Answer 8

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.

Question 9

Cytoskeletons

Answer 9

Composed of three different proteins: microtubules (25 nm), intermediate filaments (10 nm), and micro filaments (7 nm)

Question 10

Microtubules

Answer 10

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.

Question 11

Centrioles

Answer 11

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.

Question 12

Aster

Answer 12

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.

Question 13

Cilia and Flagella

Answer 13

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.

Question 14

Microfilaments

Answer 14

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.

Question 15

Intermediate Filaments

Answer 15

Heterogenous (multiple types of polypeptides).

Less dynamic. Appear important in cellular structure. Resisting mechanical stress.

Question 16

Epithial Cells “upon nipples”

Answer 16

In gut are connected via tight junctions to make impermeable.

In skin are connected via desmosomes.

Heart cells connected by gap junctions.

Question 17

Tight Junctions

Answer 17

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.

Question 18

Desmosomes

Answer 18

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.

Question 19

Gap junctions

Answer 19

pore-like connections between cells. Polypeptides and organelles cannot pass through.

Question 20

Interphase

Answer 20

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.

Question 21

Prophase

Answer 21

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.

Question 22

Metaphase

Answer 22

All chromosomes line up at center and form metaphase plate.

Question 23

Mitosis stages

Answer 23

Prophase, Metaphase, Anaphase, Telophase (PMAT)

Question 24

Anaphase

Answer 24

Spindle fibers shorten and centromeres of sister chromatids are pulled away from eachother.

Sounds like cleavage furrow of cytokenesis starts here.

Question 25

Telophase

Answer 25

Occurs in concert with Cytokenesis.

Telophase i like opposite of prophase. Nuclear membrane forms around two bunches of chromosomes, chromosomes decondense, nucleolus becomes visible.

Question 26

Oncogenes

Answer 26

Mutated genes that induce cancer.

Genes can be mutations or a result of viral genome

Question 27

Protooncogenes

Answer 27

Normal genes that under the right (or wrong) circumstances can become oncogenes.

Question 28

Tumour Suppressor Genes

Answer 28

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

Question 29

p53

Answer 29

Product of tumour suppressor gene.

Will signal for repair, but can also drive apoptosis.

Question 30

Apoptosis

Answer 30

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.