lecture 4: (week 4)

Question 1

Cytoplasm

Answer 1

Consists of all the contents that we can find within the plasma membrane excluding the cell nucleus (separated from the cytoplasm by the nuclear envelope).

Question 2

Cytoplasm consists of organelles such as

Answer 2

• The mitochondria
• golgi apparatus
• endoplasmic reticulum
• lysosome

Question 3

What’s the cytosol?

Answer 3

• Surrounds membranous organelles
• Gel-like, semifluid material that surrounds the membranous organelles and particles of the cytoplasm
• Takes up most of the cell volume.

Question 4

The cytosol is a complex mixture of?

Answer 4

• water (approx 70%)
• salts
• dissolved ions
• organic molecules.

Question 5

The pH of the cytosol is?

Answer 5

7.2

Question 6

pH of the cytosol is maintained in a range of 7.0 – 7.4 by?

Answer 6

Antiporter (Na+/H+) and Anion (Cl-/HCO3) exchanger membrane proteins

Question 7

Antiporters and anions protect the cell against

Answer 7

Excessive cytoplasmic acidification

Question 8

Cytosol is the site of numerous metabolic pathways

Answer 8

• glycolysis
• The pentose phosphate pathway
• Gluconeogenesis and synthesis of fatty acids

Question 9

Functions of the cytosol

Answer 9

• transport of metabolites
• Site for numerous metabolic pathways

-site for protein biosynthesis
(translation)

• involved in singling transduction, forms the basis of cytoskeleton
• Protects the cell against excessive cytoplasmic acidification and establishment of a steady-state pH permissive for growth and cell development

Question 10

3 cytoskeletal polymers

Answer 10

• Microtubules
• actin filaments
• intermediate filaments (a group of polymers)

Question 11

What are microtubules?

Answer 11

Hollow rods made of protofilaments (13, side by side)

most rigid of the 3 polymers (approx. >100 times that of actin filaments).

• have the most complex assembly and disassembly dynamics.
• have filament flexibility that increases with length.
• Can form almost linear tracks that can span the length of a typical animal cell.

Microtubules are hollow rods about 25 nm in diameter and about 200 nm to 25 μm long

Question 12

Microtubules consist of

Answer 12

• Tubulin
• dimers of alpha
• beta-tubulin

Question 13

Structural unit of microtubules

Answer 13

-Alpha and beta-tubulin heterodimer

dimers of alpha and beta tubulin

Question 14

microtubules structure

Answer 14

-Composed of a protein called tubulin.

Tubulin refers to a group of globular proteins.

Composed of dimers of alpha and beta tubulin.

Grow and shrink in length as needed by the addition or removal of tubulin dimers.

Question 15

Microtubules can ____ and _____ in length

Answer 15

Grow; shrink

Question 16

The space between protofilaments

Answer 16

Seam

Question 17

Distinguish the
architecture and function of the 3 cytoskeletal
polymer types and the networks they form are:

Answer 17

1. their mechanical stiffness
2. the dynamics of their assembly
3. their polarity
4. the type of molecular motors with which they
   associate

Question 18

main functions of cytoskeleton

Answer 18

• structure and support
• intracellular transport
• contractility and motility
• spatial organisation

Question 19

Alpha-tubulin bound

Answer 19

GTP

Question 20

Beta-tubulin bound

Answer 20

GTP or GDP

Question 21

alpha and beta tubulins of microtubules

Answer 21

Homologous but not identical.
Each has a nucleotide binding site.
a-tubulin has a bound GTP, that doesn’t hydrolyse.

B-tubulin may have bound GTP or GDP.

B-tubulin can hydrolyse its bound GTP to GDP plus Pi release Pi, and exchange the GDP for GTP.

Question 22

how does tubulin heterodimers join in microtubule axis

Answer 22

join end to end to form protofilaments with alternating a & b subunits

Question 23

What must happen for a heterodimer to associate with other heterodimers?

Answer 23

GTP must be ound to both a and b subunits

Question 24

are microtubules polarised

Answer 24

Yes.

microtubules are so considered polarized
polymers, as their subunits are structurally
asymmetrical at the molecular level.
• There is a ‘tip’ of the microtubule that is
GTP-bound, while beta-tubulin deeper down
the microtubule, added longer ago, are
GDP-bound

Question 25

breakdown of microtubules

Answer 25

If something happens to sever the microtubule, the the lass stable, GDP bound beta-tubulin becomes exposed and the protofilaments will start to peel away. IF this happens, the microtubule will disassemble until it hits an island of GTP - bound beta - tubulin. Can be rescued by the addition of new GTP - bound tubulin dimers.

Question 26

breakdown of microtubules

Answer 26

If something happens to sever the microtubule, the less stable, GDP bound beta-tubulin becomes exposed and the protofilaments will start to peel away. IF this happens, the microtubule will disassemble until it hits an island of GTP - bound beta - tubulin. Can be rescued by the addition of new GTP - bound tubulin dimers.

Question 27

Functions of microtubules

Answer 27

- shaping the cell - give strength and rigidity to the cell by resisting compression pressure - separating chromosomes during cell division - guiding movements of organelles - cell motility in cilia and flagella

Question 28

What does each centriole have

Answer 28

9 triplets of microtubules arranged in a ring

Question 29

What is the outer wall of the centriole cylinder typically comprised of?

Answer 29

nine triplet MTs, which are formed by one complete MT (the a- tubule) fused with two incomplete MTs (the B- and C-tubules)

Question 30

Centrioles structure

Answer 30

Cylindrical structure, found in pairs orientated at right angles to one another. The wall of each centriole cylinder is made of nine interconnected triplet microtubules. Centriolar microtubules are more stable than most cytoplasmic microtubules. The centriole, duplicates once each cell cycle.

Question 31

microfilament functions

Answer 31

- maintenance of cell shape - changes in cell shape - muscle contraction - cytoplasmic streaming - cell motility - cell diviison

Question 32

Centrosome during interphase

Answer 32

the centrosome is usually located near the nucleus. Microtubules grow out from the MTOC forming a hub * spoke array.

Question 33

What happens to centrioles prior to mitosis

Answer 33

they're duplicated

Question 34

importance of microtubules in the spindle apparatus

Answer 34

microtubules form the spindle apparatus which is vital for organisation of the cellular contents during cell division.

Question 35

mitotic spindle

Answer 35

structure that forms during cell division and separates duplicated chromosomes to ensure that they are equally divided among the two daughter cells.

Question 36

centrosome during cell division

Answer 36

duplicated centrosome helps to organize the mitotic spindle. In dividing cells, centrosomes organise MTs into the bipolar spindle apparatus upon which chromosomes segregate at mitosis.

Question 37

motor proteins

Answer 37

A protein that interacts with cytoskeletal elements and other cell components, producing movement of the whole cell or parts of the cell. They associate with their filament tracks through a "head" region, or motor domain, that binds and hydrolyzes AtP.

Question 38

cytoplasmic dynein

Answer 38

The form of dynein associated with microtubules in the cytoplasm.

Question 39

microtubules in flagella and cilia

Answer 39

have 9 + 2 arrangement of microtubules through their cross section. Typically, cells posses one or two long flagella, whereas ciliated cells have many short cilia.

Question 40

intermediate filaments functions

Answer 40

maintenance of cell shape, anchorage of nucleus and certain other organelles, formation of nuclear lamina, link to the extracellular matrix

Question 41

Microfilaments (actin filaments)

Answer 41

Most dynamic (they grow, shrink and change conformation most swiftly). Provide mechanical support to cells. Also connect the contents of the cytoplasm with cell membrane in order to support signal transduction. Vesicles and organelles are moved along microfilament tracks in a controlled manner cargo transport myosin.