Cell Organelles Midterm NYU COD 25'

How often do the following cells divide? Where are they located?

1. Labile

2. Stable

3. Permanant

1. constantly divide (includes oral mucosa cells, hematopoietic)

2. re-entry (like entering G0, then go back): liver

3. incapable of dividing (neurons, cardiac myocytes)

What is cyclosporine?

An immunosuppressant used to prevent organ rejection in transplant patients

Length of:

1. G1

2. S

3. G2

4. M

1. 5 hours

2. 7 hours

3. 3 hours

4. 1 hour

a. Prophase - 36 min

b. Metaphase - 3 min

c. Anaphase - 3 min

d. Telophase - 18 min

What happens in G1?

increase in cell size

RNA & protein synthesis

asks: is the environment stable?

What happens in S phase?

DNA duplication

centriole duplication

What happens in G2?

synthesis of proteins

synthesis of maturation promoting factor (MPF) (ex: cyclin-CDK complex)

increase in cell size

asks: is all DNA replicated? is all DNA damage repaired?

What happens in G0?

quiescent cells exit G1 and enter resting stage where cell performs its function without actively dividing

What is centrosome?

microtubule organizing center

What is a centriole?

Used by Animal Cells to produce spindle fibers that help with cell division

What happens in prophase?

Chromosomes condense

Nuclear membrane intact

Centrioles separate

Spindle apparatus formed by microtubules

What happens in prometaphase?

sister chromatids become attached to the kinetochore

nuclear envelope breaks

What happens in metaphase?

Chromosomes line up in the middle of the cell

Sister chromatids are attached to spindles on opposite poles

What happens in anaphase?

- Sister chromatids split and move to either pole (Disjunction)

- Anaphase-promoting complex (APC) trigger chromatid separation, degrading cyclin B

What is anaphase-promoting complex?

ubiquitin ligase that initiates sister chromatid separation

What happens in telophase?

Nuclear membrane reforms

Chromosomes decondense

Formation of contractile ring

What happens in cytokinesis?

division of the cytoplasm by contractile ring

The miotic spindle is made of

microtubules

The contractile ring is made of?

actin and myosin

Cyclins activate ______________, which also have inhibitors, all of which exert negative control over the cell cycle

Cyclin dependent protein kinases

Amount of CDK is _______.

Amount of Cyclin-CDK ______.

constant

varies

Cyclins are _____ by ubiquitin proteins (like APC)

degraded

CDK2

What are the functions of the cytosol?

- signal transduction (secondary messengers, protein-protein interactions)

- mRNA translation

- biochemical rxns (pentose phos. path, glycolysis, gluconeo.)

- contains cytoskeleton (microfilaments, microtubules, and intermediate filaments)

- proteasomal degradation

What are the functions of the cytoskeleton?

- maintains/ changes cell shape

- whole cell movement

- contraction

- structural integrity

Difference between G-actin and F-actin?

G-actin: monomer globular protein

F-actin: polymer filamentous chain

Myosin head with ____ attaches to ____ binding sites, undergoing configuration changes, moving _____ filament

ADP

actin

actin

Calcium is released from the ____ and binds to the troponin-tropomyosin complex to facilitate ______

sarcoplasmic reticulum

muscle contraction

In cardiac muscle contraction, the process uses _______, ______, and _______.

Cells are separated by _____ ______

adherens, desmosomes, and gap junctions

intercalculated disks

Smooth muscle contraction occurs when calcium enters the muscle, activating the _____ _______ _____ ______, which phosphorylates the regulatory ____ _____, enhancing myosin ATPase activity.

myosin light chain kinase

light chain

In non-muscle cells, actin functions include:

- maintaining cell shape

- motility

-cargo transport

The terminal web controls ______ and ______. It contains actin, _____, and ______

shape and movement

myosin and spectrin

Give examples of cells that express the following:

1. spectrin I

2. spectrin II

3. alpha-actin

4. pystrophin

1. RBCs (erythrocytes)

2. all other cells

3. muscles

4. skeletal muscle

Microvilli contain a _____ core, and its functions include:

microfilament

increased plasma membrane surface to enhance absorption and secretion of molecules

Myosin I, IV and V move cargo towards ___ end of vesicle

myosin VI moves cargo towards the ____ end

plus

minus

Microtubules are made of ______. They require ____ to polymerize.

tubulin (alpha heterodimer)

GTP

Microtubule functions

- transport/ secretion of vesicle cargo

- separation of chromosomes in mitosis/ meiosis

- contribute to cilia, flagella, motion etc

What is dynamic instability? How is it regulated?

the constant growth and degradation of microtubules. This is when GTP hydrolysis occurs fast, making the microtubule shrink faster than it grows

Its regulated by microtubule associated proteins (MAPs) by capping the plus end, preventing disassembly

What are the types of microtubules associated proteins (MAPs)?

Assembly = MrMAP and tau protein

Disassembly = Stathim and Katamin

Cargo transport is mediated by ______. The direction of traffic depends on _________. Which protein move in which direction?

motor proteins

protein domain (N-terminal=(+), C-terminal=(-))

Kinesin moves towards (+) end

Dynein moves towards (-) end

What does dynein do in normal and abnormal flagellum?

dynein= microtubule bending

abnormal=microtubule sliding

What is cilia's function?

used the increase cell surface area and increase absorption

contains hexagonal 9+2 array

What is the function of intermediate filaments?

support cell shape and fix organelles in place

What are an intermediate filaments composed of?

They are composed of hetero fiber proteins formed spontaneously and have no polarity

Examples of intermediate filaments

Cytoplasmic intermediate filaments include keratin, Neuro filaments, and Vimentin. It also includes nuclear lamina.

What are examples of homophilic adhesion?

Cadherin and IG like. Cell adheres molecules binding to another solid adhesion molecule (CAM)

What are examples of heterophile adhesion?

Selectin (CAM binding to protein)

What are Integrins and their function?

They are heterodimer's made of alpha and beta chains. Receptors are tissue and ligand specific. They interact with the cytoskeleton, cell adhesion to ECM and some cells, engage in in/out and out/in signaling.

What ligands do integrins bind to?

B1; alpha 1, 2: collagens and laminin

Alpha 3: fribronectin, laminin

Alpha 4: fibronectin, VCAM-1

Alpha 5: fibronectin

Alpha v: fibronectin, vitronectin

Cyclin D is associated with Kinase ___ and _____, functioning to put cell through ____ and ____ checkpoints

Kinases: CDK4 and CDK6

G1 and S

What does a tight junction (occluden) do?

Seals neighboring cells together in an epithelial sheet to prevent leakage

What do Zona adherens do?

Joins actin bundle in one cell, similar bundle in neighboring cell

What does a desmosome do?

Joins intermediate filaments in one cell to those of a neighbor

What does a gap junction do?

Forms channels to allow small molecules to pass cell to cell

What does a hemi desmosome do?

Anchors intermediate filaments to basil lamina

Zona = what kind of junctions

Tight and adherens

Macula= what kind of junctions

Desmosomes and hemidesmosome

What is the function of a tight junction?

Provides physical barrier to passage between cells, homophilic binding of claudins and occludens, prevents diffusion of membrane proteins

What is the function of adherens?

Cadherin mediated, calcium, dependent binding, invagination of epithelial sheets

Desmosome function

Anchoring Junction,cadherin mediated, calcium binding, homophilic

Many together impart great tensile strength to epithelial cells

Cytoskeletal elements include desmoplakin, plakoglobin, and plakophilin

Intermediate filaments attached to actin-spectrin intracellular plaque

Hemidesmosome function

Attaches to basal lamina, made of internal plaque on basal membrane

Gap junction functions

Connexon homophilic binding, pas ions and small molecules, hated channels (calcium, pH, secondary messenger)

What are process protrusions

Motile structures that constantly move towards/away from chemical gradients

What is chemotaxis

Cell process with migration in response to chemical gradient, moving towards higher concentrations

Gacher Disease Lysosomal Storage Disease

Defect in beta glucocerebrosidase

Abnormal endo and exocytosis

Functions of caveolae

Phagocytosis

Large vesicles are engulfed and trafficked elsewhere (ex: to lysosomes to be digested)

Endocytosis steps

Vesicle - early endosome - late endosome - lysosome

* golgi can also send vesicles to early endosome

Chemoreceptor arrays

- hexagonal structure

- sense and respond to chemical cues

Exocytosis steps

ER - golgi- extracellular space

Lysosome enzymes and function

- has ATPase pump proton pump to decrease pH

- opposite of its function in the mitochondria

Enzymes: nuclease, protease, lipase, phosphatase, glycolase etc

Autophagy

Autophagosomes activate in starved cells

Nucleus theories of origin and what is it made of?

Theories of origin:

Endosymbiotic theory

Protonucleus from viral cell

Made of euchromatin (11nm loosely packed inside, light in color) and heterochromatin (30nm tightly packed DNA, dark in color)

Where does mRNA exit nucleus?

Through nuclear pores

Nuclear lamina

- made of intermediate filaments

- dissolves during cell cycle

- made of heterochromatin

Nucleous functions

- made of fibrillar center, dense fibrillar and granular components

- largest amount of RNA polymerization

- MAKES RIBOSOMES

- adopter proteins used to make liquid-phase celebrations

What cell types under go what type of division?

Labile cells: constant division

Stable cells: under go re entry

Permanent cells: don't divide (neurons and cardiac cells)

What is cyclosporine

An immunosuppressant given to transplant patients

How long is each check point in the cell cycle in hours

G1: 5

S: 7

G2: 3

M: 1

G0: no division

What questions does G1 ask?

Is the environment favorable

What question does G2 ask?

Is the DNA replicated? Is the DNA repaired?

G1/S Control via p53 steps

1. Damaged DNA is arrested in G1

2. Protein kinases phosphorylate p53

3. p21 is transcribed after p53 binds

4. p21 (CDKI) is produced

5. p21 binds to G1-CDK and S-CDK and inactivates them

6. Cell cycle arrests in G1

7. Cell DNA is repaired or undergoes apoptosis

Rb gene mutations cause

Malignancies

___ and ____ prevent that cell from entering S phase

Rb and E2F

Rb is _____-phosphorylated by _____ which release E2F which transitions cells to S phase

Hypo

cyclin and CDK

What portion of the cell cycle does Rb and E2F regulate? What are Rb and E2F?

G1 and S transition

Rb= retinoblastoma protein, acts as tumor suppressor to prevent uncontrolled cell division

E2F= group of transcription factors that activate genes involved in cell cycle progression

Why don't elephants get cancer as easily?

They have more copies of the p53 gene and extra LIF genes that respond to DNA damage

p16 tumor suppressor genes specially inhibit ______ which prevents _______, which halts the cell cycle

CDK 4 and 6

Rb phosphorylation

What happens when p16 is turned off

Cancer

What are mitogens and what do they do?

They are signaling molecules that stimulate division

- trigger cell replication

- trigger mitosis

- act as growth factor

Only ___% of all cancer is diagnosed annually, which is approximately ____ cases.

3%

54,000

What cell changes cause an oral squamous cell carcinoma?

Increased mitogen, cyclin D1

Decreased p16, p53, Rb

Prophase I (Meiosis)

- chromosomes condense

- synaptonemal forms (breaks after pro 1)

-Chiasma holds crossed chromosomes together

Cohesion proteins keep _______ together across entire length

Sister chromatids

Metaphase I (Meiosis)

homologous pairs (tetrads) align at the equatorial plane and each pair attaches to a separate spindle fiber at the kinetochore

Prometaphase I (Meiosis)

the nuclear envelope breaks down and the meiotic spindles attach to kinetochores on chromosomes

Anaphase I (Meiosis)

Homologous chromosomes separate and sister chromatids remain attached

Chiasma breaks down

Telophase I (Meiosis)

chromosomes arrive at the spindle poles

Prophase II

Chromosomes condense

Metaphase II (Stage 7)

Paired chromatids line up in the middle