A&P cellular biology (1)

Question 1

3 main compartments

Answer 1

Animal cells (human) consist of 3 main compartments:

a. cell membrane
b. cytoplasm (organelles & cytosol)
c. nucleus

Question 2

cell membrane

Answer 2

A. CELL MEMBRANE
Also known as the “plasma membrane”
Functions to provide a continuous barrier to separate the cell from its external environment (including other cells, interstitial fluid, or blood).

Selective permeability – characteristic allowing only certain substances to be transported in and out of the cell (Q: What happens with a loss of this permeability? A: The cell will die! )

Question 3

fluid mosaic model

Answer 3

Fluid Mosaic Model – the model generally agreed upon to describe the cell membrane (keep in mind that the shape of the cell and its membrane varies greatly, depending on the specialty of the cell). For example => nerve cell, sperm cell, egg cell, hair, skin, and muscle cells, will all have the fundamental structures of the cell, however will look and function differently, depending on its specific role.

There is a high rate of fluctuation and 	movement of the phospholipids enabling 	the membrane to be highly fluid.

Question 4

phospholipid bilayer

Answer 4

Phospholipid bilayer (due to the fatty acid tails in the middle) is PERMEABLE to:

NON POLAR, HYDROPHOBIC, uncharged substances such as steroids, O2, CO2, N2.

Therefore it is IMPERMIABLE to POLAR, HYDROPHILIC, and charged substances such as ions & large proteins.

H2O being polar/hydrophilic will be permeable to some degree and is the exception.

Note: Although substances that are polar and hydrophilic will not pass through the membrane with ease, if the concentration, temperature, or other factors come into play, then some may pass through.

Question 5

membrane lipids

Answer 5

Membrane lipids:

Phospholipids (75%)
Cholesterol (20%)
Glycolipids (5%)

Question 6

phospholipids

Answer 6

Phospholipids (75%) – these are AMPIPATHIC! That is, they have both polar and non-polar parts (recall lecture on lipids in organic chemistry)
Phosphate heads & lipid tails (Approximately 75% of lipids in membrane)
Recall:
Polar = hydrophilic “water loving” – ratio of hydrogen to oxygen is 2:1
Non-polar = hydrophobic “water fearing” – ratio of hydrogen to oxygen is 1:1
The heads (phosphate heads) are hydrophilic and thus face outwards (i.e. towards the extracellular AND intracellular environments).
The tails are hydrophobic (2 fatty acid chains) and thus sit in between the 2 heads away from the aqueous environments.

Question 7

cholesterol

glycolipids

Answer 7

Cholesterol (20%)
Cholesterol carries an OH- group (polar) and therefore attaches to the polar heads i.e. the phosphate group.

Glycolipids (5%)
Glycolipids –“glycol” = sugar – A lipid attached to a sugar, it contains a polar carbohydrate segment that are found only on the extracellular side of the membrane. The lipid portion is hydrophobic. The role of these molecules is thought to include signal transduction, cell to cell adhesion, and binding.

Question 8

glycolax

Answer 8

Glycocalyx “sugary coat” made of the carbohydrate portions of glycolipids and glycoproteins – act as a “MARKER” to allow cells to recognize each other.

Markers are also present on the membranes of pathogens – i.e. chicken pox virus, HIV, SARS – that confer virulence and pathogenicity, and is the basis for immunogenicity.

Question 9

membrane proeins

Answer 9

Membrane Proteins:

Integral – firmly embedded into the bilayer, contains both polar/non-polar sections (tend to be more complex and larger).

Peripheral – distributed on the surface of the inner or outer membrane (attached to the polar heads of lipids or integral proteins).

Question 10

Integral & peripheral membrane proteins

Various functions- [fig 3.3 pg 63] – ‘Functions of membrane proteins’

T
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Answer 10

Integral & peripheral membrane proteins
Various functions- [fig 3.3 pg 63] – ‘Functions of membrane proteins’

1. Transporters – transports polar (hydrophilic) substances through an otherwise impermeable membrane. E.g. glucose.
2. Ion channel – selectively transports ions through.
   Can be 1-way, 2-way, single ion or multi ionic.
   E.g. sodium (Na+) and potassium (K+)
3. Receptor – “lock and key” relationship. Serves as recognition for a specific ligand. E.g. insulin and it’s corresponding receptor.
4. Enzymatic – helps dissolve/breakdown extracellular material, or acts as catalyst. E.g. lactase.
5. Linkers – helps attach and link other proteins (providing structural stability). E.g. blood clots involving fibrinogen and platelets.
6. Markers – the cell’s identity markers to help recognition by other body cells (identify it as “self”). E.g. MHC proteins.

Question 11

types of transport

Answer 11

TRANSPORT (2 types – active and passive)

2. PASSIVE – doesn’t require energy (in the form of ATP) but rather uses the KINETIC energy of substances (they move down their electrical or concentration gradients).
   * Electrical gradient – the difference in electrical charges b/w 2 regions
   * Concentration gradient – difference in concentration of a chemical from one place to another

2 main types of passive transport are
OSMOSIS and DIFFUSION

Question 12

selective permeability

Answer 12

Selective permeability allows cells to produce a chemical difference between the inside and the outside of the cell. This creates a MEMBRANE GRADIENT.

If it involved ions with charges, this would create a MEMBRANE POTENTIAL.

This is very important in biological processes & propagation of ACTION POTENTIALS (i.e. nerve impulses) (more on this in chapter 12)

Question 13

passive transport

Answer 13

Passive transport:

DIFFUSION – movement of a SOLUTE/PARTICLE from a higher to a lower concentration (i.e. down the concentration gradient) via kinetic energy. 
E.g. Opening a perfume bottle in the corner of the room => given enough time the particles/solutes will collide with each other and make their way around the entire room (no input of energy required). 
Rate of diffusion affected by 
Temperature, 
Steepness, 
Mass, 
Distance, and 
Surface area.

Integral proteins can help diffuse hydrophilic (polar) substances into/out of cell. E.g. Ions, hormones, drugs. Why? b/c these substances cannot penetrate the phospholipid tails. It basically forms a channel for these substances to pass through.

Question 14

two types of diffusion

Answer 14

Simple diffusion:
Substances move through the cell membrane down their concentration gradient. No energy/ATP required.

Facilitated diffusion:
Diffusion that is facilitated or “helped” with a trans-membrane protein.

Substances attach to one side of the membrane protein and are released on the other.

This is a passive process (no energy required) and may be slowed or maxed out, depending on the no. (#) of passive diffusion transporters.

Can be channel-mediated (transporter does not change shape but simply opens or closes) E.g. Ca2+, K+
Can also be carrier mediated (the carrier protein undergoes a conformational change during the transport) E.g. Glucose, fructose, vitamins

Question 15

osmosis

Answer 15

Osmosis (a special type of diffusion) where
the movement of a solvent (H20) goes from
HIGHER to LOWER solute concentrations.
Requires a semi-permeable membrane (impermeable to the solute).
Water moves by osmosis directly through the membrane or through specific membrane channels (aquaporins).

Question 16

osmotic pressure

Answer 16

Osmotic pressure –
pressure exerted on the solute side of the membrane. This pressure is directly proportional to the concentration of the solute.
Oncotic (colloid osmotic) pressure – pressure exerted by the presence of proteins (notably albumin) within the blood plasma.
Important for helping to “pull” water back into the venous circulation.
I.e. blood colloid osmotic pressure (BCOP)

Question 17

hydrostatic pressure

Answer 17

Hydrostatic pressure – pressure exerted by the solvent on its surroundings. Equilibrium is reached when osmosis = hydrostatic pressure. Note that in the U-tube experiment, equilibrium will not result in equal water levels.

Question 18

tonicity

Answer 18

Tonicity –
measure of a solution’s ability to change the volume of cells by altering the water content. There are solutes (usually salts & proteins) found in the solution that ALTER the existing gradient and thus alters the cell’s water content.

(Tonicity refers to the concentration of solutes in the solution.)

ISOtonic solution –
a solution where the cell’s shape will NOT CHANGE b/c the concentration of solutes is the same inside and outside of the cell. Concentration gradient of solutes and solvent are therefore the same meaning NOTHING will happen to the cell’s shape or size!

HYPERtonic solution –
higher concentration of solutes dissolved in the surrounding solution, thus there is a lower water concentration. This means there is a higher water concentration in the cell => WATER WILL LEAVE causing it to SHRINK (“crenation”)

HYPOtonic solution – lower concentrations of solutes dissolved in the surrounding solution (therefore higher water concentration). This means there is a lower water concentration in the cell => water enters the cell by OSMOSIS. The CELL WILL GROW or bulge. NB: If this exceeds the capability of the cell then it will explode and die => “lysis”.

Question 19

isotonic solution

Answer 19

a solution where the cell’s shape will not change b/c the concentration of solutes is the same inside and outside of the cell. Concentration gradient of solutes and solvent are therefore the same meaning nothing will happen to the cell’s shape or size!

Question 20

hypertonic solution

Answer 20

higher concentration of solutes dissolved in the surrounding solution, thus there is a lower water concentration. This means there is a higher water concentration in the cell => water will leave the cell causing it to shrink (“crenation”)

Question 21

hypotonic solution

Answer 21

Hypotonic solution – lower concentrations of solutes dissolved in the surrounding solution (therefore higher water concentration). **This means there is a lower water concentration in the cell => water enters the cell by osmosis. The cell will grow or bulge*. NB: If this exceeds the capability of the cell then it will explode and die => “lysis”.

Question 22

dehydration

Answer 22

Dehydration – a physiological state where there is a decrease in water concentration in the body, specifically the cells. This can be due to sweating, drugs, or not drinking enough water.

Q: What solutions do we give to rehydrate them?
A: Hypotonic solutions. Why? B/c in a hypotonic solution there is more water thus it will osmotically enter the cells.

Best way to rehydrate is to drink water, however, we also benefit from sports drinks with high levels of solutes (i.e. sugars & salts) to replenish those that we lose in our sweat.
Note: Intravenous (IV) solutions are hypotonic solutions that are placed directly into a vein to re-hydrate the person.

Question 23

active ransport

Answer 23

ACTIVE –
substances are transported against their electrical or concentration gradient (i.e. “uphill”) and thus requires ENERGY (in the form of ATP).

***E.g. Na+ and K+ ions in the sodium/potassium pump. *

Like rowing a boat upstream, you need to expend energy.

Question 24

active transport

primary

Answer 24

Primary – ATP (hydrolyzed by ATPase) is used to move a substance across the membrane against its concentration gradient (usually ions and polar solutes).

E.g. SODIUM-POTASSIUM (Na-K) PUMP in nerve and muscle cells. Cells are normally “leaky” to the ions Na+ and K+ – that is these ion channels randomly open and close and thus will allow a specific ion to move down its concentration gradient (these ions, given a certain amount of time will naturally move into or out of the cell depending on the direction of the concentration gradient). Therefore, the cell must continuously and actively “pump” Na+ out and K+ in. This allows for maintenance of the resting potential of cells for proper membrane functioning.
Found in all cells but more numerous and significant in neurons & muscle cells (more details in nervous tissue discussion)

Question 25

active transport

secondary

Answer 25

Secondary – utilizes the energy from primary transport pumps (i.e. energy from H+ or Na+ concentration gradient).
E.g. Na+/K+/Cl- channels in the kidneys.
**Analogy: Recharging a battery. You need to input energy to recharge the battery. Once recharged, the battery itself now can provide energy for other processes.
E.g. Ca2+ (calcium) pumps. Ca2+ in muscle cells require the energy derived from Na+/K+ pumps.

SYMPORTERS – move 2 substances at the same time in the SAME directions.
For e.g. glucose and amino acids

ANTIPORTERS – move 2 substances at the same time in DIFFERENT directions.
For e.g. Ca2+ or H+

Question 26

vesicular transport

Answer 26

An active process (requires ATP) in which substances move into or out of cells in VESICLES that pinch off from the cell membrane.

EXOCYTOSIS – product of metabolism and/or a substance is released out of the cell via:

Secretion – release of substances that are useful to the cell and/or organism. E.g. the secretion of hormones such as insulin or oxytocin.

BODY WANTS Excretion – release of waste products. E.g. urea in the liver. BODY’S GETTING RID OFF

Question 27

endocytosis

Answer 27

Endocytosis – process of taking substances into the cell for metabolism.
2 types of endocytosis:

E.g. Immune cell reactions => white blood cells use pseudopods (“false feet”) to form projections around viruses & bacteria they want to engulf.

Question 28

pinocytosis

Answer 28

(aka bulk phase endocytosis) “pino” – to DRINK; intake of FLUID from the surroundings. Similar mechanism as phagocytosis where there is “pinching off” of a vesicle from the cell membrane.

Question 29

transcytosis

Answer 29

Transcytosis – combination of endocytosis and exocytosis simultaneously. E.g. Antibodies in a pregnant woman. The Ab from the mother is endocytosed by a cell of the placenta, then exocytosed on the other side, thus transferring it onto the baby.

Question 30

phagocytosis

Answer 30

Phagocytosis – “phago” – to eat; cells EAT or ENGULF large solid particles like worn out cells, whole bacteria or viruses.