Cells and Organelles

Question 1

What is the role of the plasma membrane?

Answer 1

The plasma membrane encloses the cell contents and provides a barrier between the inside of the cell and the extracellular environment

Question 2

What makes the phospholipid bilayer an effective barrier?

Answer 2

The amphipathic nature of the phospholipids

Question 3

What is the role of carbohydrates and where are they found on the cell membrane?

Answer 3

Carbohydrates are found on the extracellular surface and allow cells to be recognised

Question 4

What is the role of proteins and what are the 2 different types?

Answer 4

Proteins provide a passage and allow molecules to pass through.

Integral: allow transfer of molecules across the membrane (pump, carrier, channels)
Receptor: Ligands such as EGF bind to receptor

Question 5

What is glycocalyx?

Answer 5

A coating of carbohydrates on the cell surface

Question 6

What are lipid rafts and what is their role?

Answer 6

Lipid rafts are regions enriched in particular phospholipids and cholesterol.

They act as signalling platforms to direct proteins to receptors

Question 7

What is the role of cholesterol in cell membrane?

Answer 7

It regulates fluidity of the cell membrane

Question 8

Describe the nuclear membrane

Answer 8

It is a double membrane

Question 9

What is nuclear lamina made of and what is its role?

Answer 9

It is made up of intermediate filaments

It provides mechanical support to the membrane and helps to position nuclear pores

Question 10

What is the role of nuclear pores?

Answer 10

They let molecules pass through

Question 11

Name and describe the four components of mitochondria

Answer 11

Outer membrane: selectively permeable to let pyruvate come in for Krebs’ cycle
Inner membrane: folded into multiple cristae, involved in ETC
Matrix: contains enzymes for the CaC
Intermembrane space: creates a gradient for the ETC

Question 12

What are the 2 function of the mitochondria?

Answer 12

● The site of energy production in cells.
● Triggers cell apoptosis – When irreparable DNA damage occurs, Cytochrome C which resides in mitochondria and participates in the ETC is released into the cytoplasm to trigger a proteolytic (breaking down proteins) caspase cascade to achieve apoptosis.

Question 13

What is the endoplasmic reticulum?

Answer 13

Flattened membrane which is continuous with the nuclear membrane

Question 14

Name and describe the role of the 2 types of ER?

Answer 14

Rough ER: site of protein synthesis as it is covered in ribosomes
Smooth ER: Involved in lipid synthesis and calcium storage

Question 15

Give an example of where rough and smooth ER can be found

Answer 15

Hepatocytes (liver cells) have smooth ER for lipid synthesis

Fibroblasts have ROUGH ER to produce the protein, collagen.

Question 16

What is the role of the Golgi apparatus? What process occurs there?

Answer 16

It sorts proteins.
Proteins arrive from the ER in vesicles, they pass through the golgi stack and undergo ENZYMATIC MODIFICATION which labes them for a specific location.

Question 17

Name the 3 vesicles found in the cell cytoplasm

Answer 17

Lysosomes
Endosomes
Peroxisomes

Question 18

Describe lysosomes

Answer 18

They are vesicles containing hydrolytic enzymes, they degrade unwanted particles.

Question 19

Describe endosomes

Answer 19

They are vesicles transporting molecules from the plasma membrane to lysosomes

Question 20

Describe peroxisomes

Answer 20

vesicles containing enzymes involved in oxidative

reactions e.g. biosynthesis of bile acids, detoxification, fatty acids metabolism

Question 21

Describe the role of cytoskeleton

Answer 21

Allows movement of cell components
Provides structure and support to cell
Provides mechanical linkages which allow tissue to bear stress
Allows cell to adopt different behaviours e.g. migration, division, growth

Question 22

What are the 3 types of cytoskeletal filaments

Answer 22

Microtubules
Intermediate filaments
Microfilaments

Question 23

Describe microtubules and the 3 roles they’re involved in

Answer 23

Microtubules are cylindrical tubes of tubulin.
Involved in:
● chromosomal movement - motor proteins dynein (moves cargo towards centrosomes) and kinesins (move cargo away from centrosomes)
● motility of cilia and flagella
● vesicle and organelle movement

Question 24

Describe the 4 different intermediate filaments and where they’re found. What are the roles of Intermediate filaments?

Answer 24

Keratin (in keratinocytes)
Vimentin (in fibroblasts of the dermis)
Lamin (in nuclear lamin)
Desmin (in cardiac muscle)

Involved in nuclear membrane support, chromatin and nuclear organisation

Question 25

What are 4 of the roles of Microfilaments?

Answer 25

● Cell projections e.g. stereocilia, microvilli
● Cytoplasm e.g. cell contraction, shape change
● Contractile ring e.g. cytokinesis
● Membrane extensions e.g. lamellopodia, filopodia

Question 26

What cytoskeletal component do cilia and flagella contain? What does this allow them to do and what is it primarily composed of?

Answer 26

They contain axoneme.

This allows them to bend and it is primarily composed of microtubules.

Question 27

Describe Tay Sach’s disease

Answer 27

Lysosomal storage disorder where lysosomes don’t break down lipids. This causes a build-up of lipids which destroy neurons; therefore causes progressive damage to the nervous system.

Question 28

Describe Kartageners syndrome

Answer 28

Defects in cilia and flagella due to mutations in dynein microtubule. Causes recurring respiratory infections as mucus not cleared efficiently and male infertility due to immotile sperm.

Question 29

What is Vohvinel syndrome?

Answer 29

Defective GAP junctions due to a recessive mutation in connexin protein. This causes thick, honeycomb-like calluses

Question 30

Describe Epidermolysis Bullosa Simplex

Answer 30

Defective intermediate filaments in hemidesmosomes causes lack of integrity at the dermo-epidermal junction.
This causes blistering.