Lecture 2: Cells and their organelles, stem cells

Question 1

Describe cell membrane polarity

Answer 1

Cells can have apical and basal polarity due to their plasma membrane which contain distinct protein compositions that give them distinct properties and allow for directional transport of molecules across the epithelial sheet.

Question 2

Describe the apical surface of cell membranes

Answer 2

The apical surface is the upper free surface exposed to the body exterior or the cavity of an internal organ; cell membrane which is oriented towards the lumen.

Question 3

What are the structural modifications of the apical surface?

Answer 3

• Microvilli: non-motile cytoplasmic projections which increase SA (present mainly in the absorptive columnar cells of the intestine and kidney tubules).
• Cilia and flagella: motile cytoplasmic projections.

Question 4

Describe the basolateral surface of cell membranes

Answer 4

The basolateral surface is area of the cell membrane which is oriented away from the lumen of the tubule.

Question 5

What are the structural modifications of the basolateral surface?

Answer 5

• Basal infoldings: increases the SA where ion transport occurs.
• Basement membrane: cells in contact with subjacent connective tissue
• Basal cell-to-matrix adhesions (hemidesmosomes)

Question 6

What is the composition of the basement membrane?

Answer 6

1. Basal lamina formed of adhesive glycoprotein

2. Outer reticular lamina formed of a fine network of collagen fibrils.

Question 7

What are eukaryotic cells?

Answer 7

Animal, fungi and plant cells that can be unicellular or multicellular. Plant eukaryotic cell walls are often made up of cellulose, which provides structural support. Typically undergo mitosis.

Question 8

What are prokaryotic cells?

Answer 8

Cells of bacteria (and archae) where DNA is a single molecule, found free in the cytoplasm (additional DNA is found on one or more rings called plasmids). Typically undergo binary fission .

Question 9

What is the plasma membrane of cells?

Answer 9

Component of a cell that defines the limits of the cell and the limits of sub-cellular organelles by regulating the transport of solutes into and out of the cell (selectively permeable), and by mediating cell-to-cell communication.

Question 10

Describe the structure of the phospholipid bilayer of the plasma membrane

Answer 10

Hydrophobic (“water-loving”) head and a hydrophilic (“water-hating”) tail

Question 11

Describe the composition of the plasma membrane

Answer 11

Composed of phospholipids, eg. Phosphatidylcholine.
Different plasma membranes can incorporate a number of different proteins to increase permeability of membrane, alter its function and aid in the transport of particular proteins/ solutes across the membrane.

Question 12

What is passive transport?

Answer 12

Movement of solutes across a membrane, typically down their conc. gradient. Movement does not require energy.

Question 13

What is active transport.

Answer 13

Movement of solutes across a membrane, typically against their conc. gradient. Movement often requires energy.

Question 14

What is the function of the organelle mitochondria?

Answer 14

Mitochondria are the ‘energy powerhouse’ of the cell and the site of ATP generation.

Question 15

Describe the structure of mitochondria

Answer 15

The mitochondria has an outer membrane which is permeable and an inner membrane which is far less permeable and is heavily folded to create cristae to increase surface area for ATP production. Inside the inner membrane is the matrix.

Question 16

How can mitochondria and ATP production be halted?

Answer 16

• Inhalation of hydrogen cyanide or ingestion of potassium cyanide inhibits the mitochondrial electron transport chain
• Mitochondrial myopathies are point mutations in genes encoding the mitochondrial tRNA lysine.

Question 17

What is the function of the organelle Golgi apparatus?

Answer 17

The Golgi apparatus is required for modification, packaging and sorting of proteins and lipids destined either for secretion or for another organelle.

Question 18

What are lysosomes?

Answer 18

Lysosomes are cytoplasmic vesicles that are packed with degradative enzymes and are usually transported to sites of intracellular digestion.

Question 19

What are peroxisomes?

Answer 19

Peroxisomes are small cytoplasmic vesicles which house environment for reactive H2O2 generation for the breakdown/oxidation of fatty acids. Detoxify toxic substances such as ethanol (via catalase).

Question 20

Describe the role of other organelle within cells

Answer 20

Nucleus (eukaryotic)- contains main genome responsible for RNA and DNA synthesis.
Endoplasmic Reticulum (ER)- responsible for the synthesis of most lipids and proteins for distribution around the cell.
Endosomes- responsible for the sorting of endocytosed material.
Chloroplasts (in plant cells)- ATP synthesis and carbon fixation by photosynthesis

Question 21

What is the cytoskeleton?

Answer 21

The cytoskeleton is a microscopic network of protein filaments and tubules in the cytoplasm of many living cells, that pulls the chromosomes apart during mitosis, drives and guides the intracellular traffic of organelles, supports the plasma membrane, enables some cells to move, and controls cell shape.

Question 22

What are the 3 major components of the cytoskeleton?

Answer 22

1. Actin filaments: polymers of actin monomers. Can form contractile bundles and microvilli and also carry cargo-bearing motor proteins (e.g. myosin).
2. Intermediate filaments: made of a family of fibrous proteins that are twisted into ropes to provide tensile strength which is needed to maintain cell shape.
3. Microtubules: polymers of tubulin dimers.

Question 23

What are stem cells?

Answer 23

Stem cells are cells that can divide without limit and have not yet undergone terminal differentiation, thus they have the ability to specialise into any cell.

Question 24

How do embryonic stem cells differ from adult stem cells?

Answer 24

Embryonic stem cells are totipotent (or pluripotent) and have the ability to differentiate into any cell type, whereas adult stem cells, such as those found in the gut and the skin, are multipotent and can only divide to replace certain cell types .

Question 25

What are hematopoietic stem cells (HSCs)?

Answer 25

Hematopoietic stem cells (HSCs) are the stem cells that give rise to other blood cells.

Question 26

What are induced pluripotent stem cells (IPS) ?

Answer 26

pluripotent stem cell derived from adult somatic cells that have been reprogrammed through inducing genes and factors to become pluripotent, and so have the potential to replace a multitude of cells within the body.

Question 27

What are the 2 ways in which cells die?

Answer 27

1. Necrosis- cell lysis.

2. Apoptosis- programmed cell death

Question 28

What happens during cell apoptosis?

Answer 28

Signalling processes within the cell activate intracellular suicide proteases which degrade intracellular structures and organelles, collapse the cytoskeleton, and fragment the cell into mini-cells for phagocytosis.

Question 29

What happens during cell necrosis?

Answer 29

Cell membranes’ integrity is destroyed, releasing its contents; cell components are degraded by extracellular enzymes and phagocytic cells.

Question 30

What are mitochondrial myopathies?

Answer 30

Point mutations in genes encoding the mitochondrial tRNA lysine.