Cells and their Environment

Question 1

How do cells maintain their shape and move

Answer 1

Cytoskeleton : microtubules
intermediate filaments
actin microfilaments

Question 2

Microtubules

Answer 2

found in cilia and flagellae
dimers of α and β tubulin arranged as hollow cylinders
require microtubule organising centre for assembly
25nm

Question 3

Intermediate filaments

Answer 3

interact with other elements of cytoskeleton and support desmosomes
rope-like twisted fibres of various proteins
10nm

Question 4

Actin microfilaments

Answer 4

form skeleton of microvilli and stereocilia
polar double stranded helical array of G actin
7nm

Question 5

Centrioles

Answer 5

cylindrical structures
groupings of microtubules arranged in a 9 + 0 pattern
help to organise assembly of microtubules during cell division

Question 6

How do cells interact with each other?

Answer 6

cell junctions

Question 7

Appearance of cell junctions

Answer 7

occluding
adherent
desmosomes
gap junction

Question 8

Occluding

Answer 8

tight junction - zonula occludens
pentalaminar
limit movement of molecules through intracellular space
prevent movement of membrane from apical to lateral surface of cell

Question 9

Adherent junction

Answer 9

zonula adherens (intermediate)
provide mechanical stability by linking cytoskeleton to adjacent cells
20nm gap
cell adhesion molecules eg. cadherins, integrins
bind to intracellular molecules

Question 10

Desmosomes

Answer 10

macula adherens
link to intermediate filaments in cytoplasm
30 nm gap
discoid
specialised cadherins - desmocollin and desmoglein between cells
intracellular attachment plaques anchor
perpendicular to basement membrane

Question 11

How are hemidesmosomes different to desmosomes

Answer 11

face basement membrane
integrins, laminin, collagen
cell to matrix

Question 12

Gap junction

Answer 12

allow direct communication between adjacent cells
allow passage of ions, AAs, sugars, 2nd messengers, metabolites
permits coordinated cell activity
made of connnexins which assemble into connexons

Question 13

How do cells interact with their surroundings?

Answer 13

extracellular matrix

Question 14

Extracellular matrix

Answer 14

mechanical and structural support
influences extracellular communication
consists of: ground substance and fibres

Question 15

Ground substance

Answer 15

glycosaminoglycans, proteoglycans, multiadhesive glycoproteins
occupies large volume for small mass
hydrophilic: attracts water and Na+ - extracellular fluid

Question 16

Glycosaminoglycans

Answer 16

GAGs, acidic

negatively charged hydroxyl, carboxyl and sulphydryl groups

Question 17

Fibres

Answer 17

collagen: tensile strength
eg. reticulin (type III collagen, branched)
elastin: stretching and recoil

Question 18

Structural glycoproteins

Answer 18

filamentous: fibrillin - micro, links to elastin
fibronectin - links to cells via integrin
non-filamentous (link cells and ECM):
laminin - component of basement membrane
entactin - binds laminin to type IV collagen
tenascin - binds to integrins

Question 19

Diseases of extracellular matrix

Answer 19

Ehlers-Danlos syndrome
Marfans syndrome
Scurvy
Homocystinuria
Mucopolysaccharidoses

Question 20

Ehlers-Danlos syndrome

Answer 20

extensible skin, lax joints

defective genes coding for type I collagen

Question 21

Marfans syndrome

Answer 21

defective genes coding for fibrillin

rupture of aorta

Question 22

Homocystinuria

Answer 22

homocysteine interferes with cross linking of collagen