Lecture 6: Regulation of Animal Cell Shape

Question 1

What does the cytoskeleton do?

Answer 1

helps maintain cell shape.
and position of organelles
with in cells.

the cytoskeleton rapidly
disassembles and
reassembles, unlike the
body’s skeletal system.
this ability allows rapid
changes in cell shape.

the cytoskeleton is highly
dynamic but still provides
stability.

Question 2

What is the three main components of the cytoskeleton?

Answer 2

Microtubules
Microfilaments
Intermediate Filaments

Question 3

What are microtubules made out of?

Answer 3

Tubulin subunits

Question 4

What are microfilaments made out of?

Answer 4

Actin subunit

Question 5

What are intermediate filaments made out of?

Answer 5

Keratin Proteins
Fibrous subunit (keratins coiled together)

Question 6

What do microtubules do?

Answer 6

Resist compression and help maintain cell shape.

they also provide cell motility

flagella: snake-like motion
cilia: rowing-like motion

Microtubules are also
involved in organelle
motility within the cell

ATP-powered motor
proteins can “walk”
organelles along
microtubules

Allows vesicles, or
other organelles, to be
transported to specific
targets within the cell

Question 7

What do microfilaments do?

Answer 7

Microfilaments resist tension

The cortical network under the
plasma membrane helps make
this region less fluid and thus
maintains cell shape

Interactions between actin and
motor proteins such as myosin
support cell movement

Question 8

Actin-myosin interactions allow:

Answer 8

• muscle contraction.
• amoeboid movement.
• cytoplasmic streaming in
  plants.

Question 9

What do Intermediate filaments do?

Answer 9

Are made of various proteins
including:
- keratins in hair.
- lamins in the nucleus.
- neurofilaments in neurons.

Supercoiled into “cables”
Less dynamic than microtubules
or microfilaments
Intermediate Filaments form
relatively permanent cellular
structures

Question 10

What is the name of the the three ways cells are joined together?

Answer 10

Tight Junctions
Desmosomes
Gap Junctions

Question 11

Tight Junction

Answer 11

Hold neighbouring cells tightly
pressed together

May form a continuous seal

Prevents movement of fluid across cell layers

Question 12

what type cell junction prevents movement of fluid across cell layers

Answer 12

Tight Junctions

Question 13

Desmosomes

Answer 13

Anchoring junction

Provide attachments between
sheets of cells e.g. muscle

Act like rivets (a “torn muscle” is a torn desmosome)

Connected into the cell by
intermediate filaments

Question 14

Gap Junctions

Answer 14

A point of cytoplasmic contact
between two cells

Ions and small molecules can
pass from cell to cell

Allows rapid cell to cell
(intercellular) communication

Question 15

What cell junction allows rapid cell to cell

(intercellular) communication

Answer 15

Gap Junction

Question 16

How are cells joined together?

Answer 16

In many tissues
cells do not
make direct
contact with
other cells

Cells lie within
an Extracellular
Matrix (ECM)
the composition
of which varies
between tissues

Question 17

What is the Extracellular Matrix made up of?

Answer 17

The ECM is composed of
material secreted by cells

This secretion occurs by
constitutive exocytosis

Most ECM proteins are
glycoproteins (protein with
added carbohydrates)

The most abundant ECM
glycoprotein is collagen

Collagen fibres have great
tensile strength

Question 18

Where are the collegen fibres in the Extracellular matrix embedded?

Answer 18

The collagen fibres are Proteoglycan Matrix
embedded in a proteoglycan
complex matrix (green on figure)

Question 19

What are proteoglycans? What do they do?

Answer 19

Proteoglycans are proteins
with extensive sugar
additions.

Proteoglycans trap water
within the ECM

Water resists compression
and thus helps retains
tissue shape.

Question 20

Extracellular Matrix (ECM)

Answer 20

Other glycoproteins
(fibronectins)
attach cells to
ECM.

Membrane proteins
(integrins) connect
the ECM to
cytoskeleton.

Providing a
communication link
from ECM to the
cell interior

Question 21

What are the three major components of the

cytoskeleton?

Answer 21

Microfilaments
Intermediate Filaments
Microtubules

Question 22

What are the three main cell junctions

Answer 22

Tight Junction
Desmosomes
Gap Junction