Unit 1 - Cells, Membranes, and Homeostasis

Question 1

What are the 3 observations of cell theory

Answer 1

1. All organisms are made up of cells
2. The cell is the fundamental unit of life
3. Cells come from preexisting cells

Question 2

what two types of cells do you get

Answer 2

unicellular - single cell (bacteria, amoeba)
multicellular - hundreds to thousands of cells (mammals, plants)

Question 3

Why are cells classified as living

Answer 3

They reproduce, respond to the environment, harness energy, and evolve

Question 4

What are some defining characteristics of prokaryotes

Answer 4

• No nucleus (genetic info is concentrated in the nucleoid)
• Flagella (motility)
• Small size (1 to 2 micrometers in diameter)
• High ratio of SA:V (large SA available for absorption relative to V of the cell)

Question 5

What are some defining characteristics of eukaryotes

Answer 5

• Nucleus (DNA, multilinear chromosome)
• Internal membranes (compartmentalized organelles with special features)
• Larger size (8 to 300 micrometers)
• Different lipid types in the membrane

Question 6

What are some similarities between prokaryotes and eukaryotes

Answer 6

Both have cytoplasm, cell walls/membranes, DNA, and make proteins

Question 7

How is transcription and translation different in eukaryotes vs prokaryotes

Answer 7

Eukaryotes - Transcription takes place in the nucleus first, and translation takes place later in the cytoplasm
Prokaryotes - Translation occurs as soon as mRNA is transcribed from the DNA template

Question 8

What is the main component of membranes & what else

Answer 8

lipids & proteins (embedded in or associated with the proteins), carbohydrates (usually attached to lipids and proteins)

Question 9

Describe the lipid bilayer found in most cells

Answer 9

phospholipids (made up of a glycerol backbone attached to a phosphate group and two fatty acids)

Question 10

What allows the phospholipid bilayer to form a barrier in an aqueous environment

Answer 10

The phosphate group which is hydrophilic (polar) and the two fatty acid tails which are hydrophobic (nonpolar)

Question 11

what are molecules that have both hydrophilic and hydrophobic regions

Answer 11

amphipathic

Question 12

explain why membranes are said to be a fluid mosaic model

Answer 12

Because the lipid bilayer is a structure within which molecules move laterally (it is fluid) and is a mixture (mosaic) of different types of molecules (lipids, proteins, and carbohydrates)

Question 13

What determines the level of fluidity of the membrane

Answer 13

The length of the tail (longer tail = less fluid) because more surface area to participate in van der waal’s forces
The no. of carbon-carbon double bonds (less bonds = less fluid) due to kinks in the fatty acid tails, which reduces tightness of packing

Question 14

Give an example of another substance that influences fluidity

Answer 14

cholesterol. The amphipathic nature allows it to insert itself into the lipid bilayer so that its head interacts with the hydrophilic head group of phospholipids and the ring structure participates in van der waal’s forces with the hydrophobic fatty acid chains.

Question 15

What exactly does cholesterol do

Answer 15

when temperature increases - cholesterol will decrease membrane fluidity by interacting their rigid ring structure with the fatty acid tail to reduce mobility
When temperature decreases - cholesterol will prevent phospholipids from packing tightly with other phospholipids, increasing mobility

Question 16

What is lipid flip-flop

Answer 16

the spontaneous movement of lipids between layers of the bilayer

Question 17

What different functions do proteins serve

Answer 17

1. Transporters (moving ions or molecules across the membrane
2. Receptors (allow the cell to receive signals from the environment)
3. Enzymes (catalyse chemical reactions)
4. Anchors (attach to other proteins and help to maintain structure and shape)

Question 18

what are the two groups of membrane proteins

Answer 18

1. Integral membrane proteins (can’t be separated unless destroying the membrane)
2. Peripheral membrane proteins (temporarily associated with the lipid bilayer or with integral proteins through weak noncovalent interactions)

Question 19

what are most integral membrane proteins

Answer 19

Transmembrane proteins (spanning the entire lipid bilayer)

Question 20

Explain the different regions of transmembrane proteins on a receptor

Answer 20

3 regions -
2 hydrophilic regions - one protruding outwards, and one inwards
– exterior hydrophilic region - interacts with signaling molecules
– interior hydrophilic region - interacts with other proteins in the cytoplasm of the cell to pass along the signal
1 hydrophobic region - spans the entire interior hydrophobic region of the membrane

Question 21

What do peripheral membrane proteins do

Answer 21

• associated with external or internal environment
• interact with the polar heads of lipids or with integral membrane proteins
• can play a role in transmitting information received from external signals
• can also limit the ability of transmembrane proteins to move within the membrane and assist proteins in clustering in lipid rafts

Question 22

what is used to demonstrate protein mobility

Answer 22

fluorescence recovery after bleaching FRAP

Question 23

What is homeostasis

Answer 23

the active maintenance of a stable environment within cells and organisms, done by the cell membrane and organelles

Question 24

how does the cell membrane maintain homeostasis

Answer 24

Through its selectively permeable membrane, it lets certain molecules in and out freely, it lets others out under conditions, and it prevents others from passing through at all

Question 25

how is it selectively permeable

Answer 25

combination of lipids and proteins.
- hydrophobic interior prevents ions and charged molecules
- macromolecules (polysaccharides and proteins are too large to move through)
- O2 and CO2, and lipids (nonpolar molecules) can move through
- small uncharged molecules (H2O) can move through at a limited extent

Question 26

What is simple diffusion

Answer 26

passive transport that involves the movement of substances from an area of high concentration to an area of low concentration, directly through the membrane (O2 and CO2, and hydrophobic molecules)

Question 27

what is facilitated diffusion

Answer 27

molecules move passively down concentration gradient through protein transporters

Question 28

What are the two types of membrane transporters (proteins)

Answer 28

1. Channel proteins - provides an opening between the inside and outside of the cell through which certain molecules can pass depending on size and shape (gated channels respond to chemical or electrical signals)
2. Carrier proteins - bind to and then transport molecules. the membrane protein will change shape during the transportation of the molecule.

Question 29

how does water move through the membrane

Answer 29

mainly passively (due to molecules being small enough) through the bilayer by means of simple diffusion. also by channel proteins called aquaporins (facilitated diffusion)

Question 30

Explain osmosis

Answer 30

Movement of water from regions of high water concentration to lower water concentration, or from regions of lower solute concentrations to higher solute concentrations

Question 31

What is active transport

Answer 31

the movement of molecules from low to high concentration gradient. requiring a form of input energy

Question 31

How can osmosis be prevented

Answer 31

by applying force to the apartment with higher solute concentration, decreasing osmotic pressure

Question 32

how does the membrane move substances during active transport

Answer 32

through transport proteins that are embedded in the cell membrane, some of these proteins act as pumps, using energy directly to move a substance in or out of a cell

Question 33

example pf active transport pump

Answer 33

Sodium-potassium pump, inside cell - low Na+, high K+, outside cell - high Na+, low K+.
moves Na+ out and K+ in.
uses energy which comes from the chemical energy stored in adenosine diphosphate (ADP) and inorganic phosphate (Pi)

Question 34

what are antiporters & symporters

Answer 34

transport proteins that transport substances in opposite directions
& proteins that move substances in the same direction

Question 35

What is secondary active transport

Answer 35

does not use ATP directly. uses an electrochemical gradient (difference in charge) that is formed due to the build up of small ions on one side of the membrane, as they cannot cross the lipid bilayer

Question 36

Example of secondary active transport

Answer 36

Proton (H+) pump

Question 37

What direction do these charged molecules move in

Answer 37

from an area of like charges to unlike charge

Question 38

describe the movement of protons

Answer 38

always from regions of higher to lower concentration

Question 39

Explain the difference in the following solutions:
1. Isotonic
2. Hypotonic
3. Hypertonic

Answer 39

1. the outside water concentration = the same as the inside
2. the outside water/solute concentration is lower than the inside (contractile vacuoles)
3. the outside water/solute concentration is higher than the inside

Question 40

what are co-transporters

Answer 40

the coupling of the favourable movement (with its concentration gradient) of one molecule, with the unfavourable movement (against its concentration gradient) of another molecule