Molecular Cell Biology- Cells and their Organelles: stem cells

Question 1

Single celled organisms

Answer 1

Bacteria, some free-living eukaryotes such as yeast and protozoa

Question 2

Apical

Answer 2

Oriented towards the lumen

Question 3

Basal/basolateral

Answer 3

Oriented away from lumen

Question 4

What does it mean when it is said that cells are polarised?

Answer 4

They have apical and basal polarity

Question 5

Differences between eukaryotic and prokaryotic cells

Answer 5

Eukaryotic cells have membrane-bound organelles in cytoplasm, eukaryotic cells are larger, eukaryotes have their DNA in the form of chromatin, eukaryotes have no cell wall and no chloroplasts (except plants)

Question 6

Microtubule

Answer 6

Gives cell structure

Question 7

Intermediate Filaments

Answer 7

Gives cell structure

Question 8

Phospholipids. Structure of hydrocarbon tails.

Answer 8

Hydrophilic heads and hydrophobic tails cause them to spontaneously arrange themselves into bilayers. Tail has a bend which is important to function of lipid

Question 9

Membrane lipid compositions and the importance of the effects of lipid composition

Answer 9

Varying lipid composition of membranes varies the physical properties of the membrane. Important because membranes fulfill many different roles in a cell so properties must vary

Question 10

Flip Flop movement (transverse diffusion) and example. How fast is the process

Answer 10

When a lipid moves from one surface to another e.g. phospholipid changing layer it is in in the bilayer. Very slow, often needs an enzyme

Question 11

Flippase

Answer 11

Aids Flip-Flop movement

Question 12

What kinds of molecules is the membrane fully permeable and slightly permeable to? Give examples where necessary

Answer 12

Fully permeable to gases and small uncharged polar molecules like ethanol. Slightly permeable to small uncharged polar molecules like urea and water.

Question 13

What kinds of molecules is the membrane impermeable to? Give examples

Answer 13

Large uncharged polar molecules like glucose/fructose. Ions like K+. Charged polar molecules like proteins and amino acids.

Question 14

Cytosol

Answer 14

The aqueous component of the cytoplasm of a cell. Contains many metabolic pathways and is site of protein synthesis

Question 15

Types of proteins in a membrane and their function

Answer 15

Transporters (involved in movement of molecules across membrane), Anchors (mediators of membrane associations), receptors (for recognition and receiving chemical signals) and enzymes

Question 16

Use of H+ ions to provide energy

Answer 16

Electron transport drives pump that pumps protons across mitochondrial membrane and the proton gradient is used by ATP synthase to make ATP

Question 17

Golgi apparatus

Answer 17

Modifies, packages and sorts proteins and lipids destined for another organelle or for secretion via exocytosis

Question 18

Lysosomes, give function too

Answer 18

Cytoplasmic vesicles packed with degradative enzymes; the main sites of intracellular degradation/digestion

Question 19

Peroxisomes, give function too

Answer 19

Cytoplasmic vesicles which provide a contained environment for reactive H2O2 generation. Uses oxidation reactions. The main function of oxidation reactions in peroxisomes is the breakdown of fatty acids and toxic molecules. Detoxifies toxic substances like ethanol via catalase

Question 20

Endosomes

Answer 20

Responsible for sorting of endocytosed material

Question 21

What does the cytoskeleton consist of and what does it do?

Answer 21

Consists of actin filaments, intermediate filaments and microtubules. Pulls chromosomes apart during mitosis, supports plasma membrane, controls cell shape, enables some cells to move and drives/guides the intracellular traffic of organelles, proteins and RNA

Question 22

Actin filaments

Answer 22

Polymer of actin monomer,filament is 7 nm in diameter . Necessary for movement, can form contractile bundles and microvilli. May associate with myosin to form powerful contractile structures, carry cargo-bearing motor proteins e.g. myosin. Can grow, dissolve and reform.

Question 23

Intermediate Filaments

Answer 23

10nm diameter, made of various fibrous proteins depending on cell type (keratin in epithelial, vimentin in smooth muscle cells and white blood cells, neurofilament proteins in neurones, Lamins in nucleus). Twisted into ropes, providing tensile strength. Needed to maintain cell shape

Question 24

Microtubules

Answer 24

20nm diameter. Polymers of tubulin dimers. Organised from structures such as the centrosome. Form the spindle in mitosis. Important in cell shape and movement. Carries cargo-bearing motor proteins. They are molecular motorways, allowing proteins etc to be transported from one end of cell to the other

Question 25

Name two motor proteins and discuss how they move along microtubules

Answer 25

Dynein and kinesin. These motor proteins walk along microtubules using energy from ATP. Dynein walks towards the negative end of the microtubule and kinesin towards the positive end.

Question 26

Stem cells defining properties

Answer 26

It is not itself terminally differentiated. Immortal. It can divide without limit, when stem cell divides daughter cells can choose to either remain a stem cell or begin journey to terminal differentiation. Division slows as one gets older.

Question 27

Where are stem cells particularly needed and how do they stay undifferentiated

Answer 27

Stem cells are especially needed in areas where there is a recurring need to replace differentiated cells that cannot themselves divide. To keep stem cells undifferentiated, keep the stem cells near their stem cell niche. A stem-cell niche is an area of a tissue that provides a specific microenvironment, in which stem cells are present in an undifferentiated and self-renewable state.

Question 28

Pluripotent

Answer 28

Can differentiate into all body cells but not placental cells

Question 29

Totipotent

Answer 29

Can differentiate into any type of body cell AND placental cells. Only embryonic cells after first few divisions are considered to be totipotent

Question 30

Multipotent

Answer 30

Can differentiate into a few types of cell. More limited. Adult stem cells are multipotent. Multipotent cells only differentiate to make a specific specialised tissue

Question 31

Stem cells in the skin

Answer 31

Important in skin replacement and wound healing

Question 32

Haemopoietic stem cells

Answer 32

Differentiate into all sorts of blood cells

Question 33

Induced Pluripotent Stem Cells (IPS)

Answer 33

Adult stem cells that have been modified to behave like embryonic pluripotent stem cells

Question 34

Advantages and disadvantages of IPS

Answer 34

Cells taken from a patient should not elicit an immune response. Fewer ethical issues. Theoretically any cell type could be replaced. But more research needs to be done on developmental pathways. Transplanted stem cells may develop into cancer cells

Question 35

Necrosis (lysis)

Answer 35

A form of cell death. Cells lyse (CM ruptures) and burst. CM integrity destroyed and soluble contents are released into tissue fluids. Cell components degraded by the actions of extracellular enzymes and phagocytic cells engulf fragmentary remains. Triggers immune response (inflammation)

Question 36

Apoptosis

Answer 36

A form of cell death. The normal pathway. Signalling processes in cell activate intracellular suicide proteases which degrade intracellular structures and organelles, collapse cytoskeleton and fragment the cell into mini-cells to be engulfed by phagocytes for degradation. Apoptotic cell dies without damaging neighbours