MEC322: Cells

Question 1

How many cells are in the body?

Answer 1

about 100 trillion cells (average human adult)

Question 2

What is the largest and smallest cell?

Answer 2

The largest cell, a single neuron, can have an axon over a meter long. A red blood cell has a diameter of 8 μm (micrometers).

Question 3

What are the three main parts of a cell?

Answer 3

Plasma membrane
Nucleus
Cytoplasm – cytosol and organelles

Question 4

What is the structure and purpose of the plasma membrane?

Answer 4

Forms a cell’s flexible outer surface, separating the cell’s internal environment from its external environment.
It regulates the flow of materials into and out of a cell to maintain the appropriate environment for normal cellular activities.
It also plays a key role in communication among cells and between cells and their external environment.

Question 5

What is the basic framework of the plasma membrane?

Answer 5

the lipid bilayer, two tail-to-tail layers made up of three types of lipid molecules: phospholipids, cholesterol, and glycolipids.

Question 6

What are two types of proteins in the plasma membrane?

Answer 6

The proteins in a membrane are of two types: integral and peripheral.
Integral proteins extend through the lipid bilayer.
Peripheral proteins are loosely attached to the exterior or interior surface of the membrane.

Question 7

Is the plasma membrane permeable or selectively permeable?

Answer 7

selectively permeable—it allows some substances to move into and out of the cell but restricts the passage of other substances.

Question 8

What is the lipi bilayer permeable and impermeable to?

Answer 8

The lipid bilayer is permeable to water and to nonpolar (lipid-soluble) molecules (fatty acids, O2, CO2, etc.)
The lipid bilayer is impermeable to ions and large, uncharged polar molecules such as glucose and amino acids.

Question 9

How do large molecules such as proteins pass through the plasma?

Answer 9

They are unable to pass through the plasma membrane except by transport within vesicles.

Question 10

What allows small and medium-sized water-soluble materials to cross the membrane?

Answer 10

Integral proteins

Question 11

Why is it important for materials to move across a plasma membrane?

Answer 11

Certain substances must move into the cell to support metabolic reactions. Other materials must be moved out because they have been produced by the cell for export or are cellular waste products.

Question 12

Name the types of body fluid

Answer 12

Intracellular fluid (ICF) – fluid in body cells (~ 2/3rd of all body fluid volume)
Extracellular fluid (ECF) – fluid outside cells
Interstitial fluid – ECF between cells in tissues
Blood plasma – ECF in blood vessels
Lymph – ECF in lymphatic vessels
Cerebrospinal fluid (CSF) – surrounds the brain and spinal cord

Question 13

Describe the two methods for substances to move across the plasma membrane.

Answer 13

Passive processes – substance moves down its concentration gradient through the membrane, using only its own energy of motion (kinetic energy), include simple diffusion and osmosis.
Active processes – cellular energy, usually in the form of ATP, is used to “push” the substance through the membrane “uphill” against its concentration gradient. An example is active transport.

Question 14

What is diffusion?

Answer 14

A passive process in which a substance moves due to its kinetic energy. Areas of high concentration move to areas of low concentration.

Question 15

What is simple diffusion?

Answer 15

when substances diffuse across a membrane through the lipid bilayer.
eg. fatty acids, steroids, fat-soluble vitamins, oxygen, carbon dioxide.

Question 16

What is facilitated diffusion?

Answer 16

In this process, an integral membrane protein assists a specific substance to move across the membrane. The membrane protein can be either a membrane channel or a carrier.

Question 17

What is osmosis?

Answer 17

a passive process in which there is a net movement of water through a selectively permeable membrane.
Water moves by osmosis from an area of higher water concentration to an area of lower water concentration

Question 18

What is an isotonic solution?

Answer 18

Any solution in which cells maintain their normal shape and volume is called an isotonic solution (the concentrations of solutes are the same on both sides).

Question 19

What is a hypotonic solution?

Answer 19

A hypotonic solution is a solution that has a lower concentration of solutes (higher concentration of water).
cell swells

Question 20

What is a hypertonic solution?

Answer 20

A hypertonic solution has a higher concentration of solutes (lower concentration of water).
cell shrinks

Question 21

What does the function of the plasma membrane depend on?

Answer 21

type of proteins that are present 
some form:
receptors 
ion channels
proteins act as enzymes 
carrier proteins (change shape)
cell identity markers

Question 22

What is dialysis good for?

Answer 22

removing small molecules from the bloods

Question 23

What is ultra filtration better than dialysis for?

Answer 23

removal of fluid and medium sized molecules

Question 24

What does URR measure?

Urea Reduction Ratio

Answer 24

How effectively a dialysis treatment removed waste products from the body

Question 25

What percentage URR are patients said to live longer and have fewer hospital visits?

Answer 25

60%

Question 26

Describe the measurement of URR

Answer 26

measured every 12-14 treatments so once a month

URR may vary considerable so average should not exceed 65%

Question 27

How do you calculate dialysis efficiency?

Answer 27

K x t / V
K- dialyser clearance, rate at which blood passes thru the dialyser
t - time
V - volume of water in patients body

Question 28

What are the limitations of the dialysis efficiency equation?

Answer 28

k values are measured by manufacturer with water so underestimate
patients do not all have same water percentage
bigger solute removal is not taken into account

Question 29

What is active transport?

Answer 29

an active process where cellular energy is used to transport substances across the membrane against a concentration gradient

Question 30

What is a vesicle?

Answer 30

a small round sac formed by budding off from an existing membrane

Question 31

What do vesicles do?

Answer 31

transport substances from one structure to another within cells, take in substances from extracellular fluid and release substance into extracellular fluid

Question 32

What is endocytosis?

Answer 32

– in which materials move into a cell in a formed vesicle

Question 33

What is exocytosis?

Answer 33

in which materials move out of a cell by the fusion of a vesicle.
results in secretion or liberation of materials out of cell

Question 34

What are the two types of endocytosis?

Answer 34

Phagocytosis is “cell eating”. Large solid particles, such as whole bacteria or viruses or dead cells, are taken in by the cell.
Bulk-phase endocytosis (pinocytosis) is “cell drinking.” The cells take up tiny droplets of extracellular fluid.