Unit 1 - Cells, Membranes, and Homeostasis Flashcards
What are the 3 observations of cell theory
- All organisms are made up of cells
- The cell is the fundamental unit of life
- Cells come from preexisting cells
what two types of cells do you get
unicellular - single cell (bacteria, amoeba)
multicellular - hundreds to thousands of cells (mammals, plants)
Why are cells classified as living
They reproduce, respond to the environment, harness energy, and evolve
What are some defining characteristics of prokaryotes
- 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)
What are some defining characteristics of eukaryotes
- Nucleus (DNA, multilinear chromosome)
- Internal membranes (compartmentalized organelles with special features)
- Larger size (8 to 300 micrometers)
- Different lipid types in the membrane
What are some similarities between prokaryotes and eukaryotes
Both have cytoplasm, cell walls/membranes, DNA, and make proteins
How is transcription and translation different in eukaryotes vs prokaryotes
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
What is the main component of membranes & what else
lipids & proteins (embedded in or associated with the proteins), carbohydrates (usually attached to lipids and proteins)
Describe the lipid bilayer found in most cells
phospholipids (made up of a glycerol backbone attached to a phosphate group and two fatty acids)
What allows the phospholipid bilayer to form a barrier in an aqueous environment
The phosphate group which is hydrophilic (polar) and the two fatty acid tails which are hydrophobic (nonpolar)
what are molecules that have both hydrophilic and hydrophobic regions
amphipathic
explain why membranes are said to be a fluid mosaic model
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)
What determines the level of fluidity of the membrane
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
Give an example of another substance that influences fluidity
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.
What exactly does cholesterol do
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
What is lipid flip-flop
the spontaneous movement of lipids between layers of the bilayer
What different functions do proteins serve
- Transporters (moving ions or molecules across the membrane
- Receptors (allow the cell to receive signals from the environment)
- Enzymes (catalyse chemical reactions)
- Anchors (attach to other proteins and help to maintain structure and shape)
what are the two groups of membrane proteins
- Integral membrane proteins (can’t be separated unless destroying the membrane)
- Peripheral membrane proteins (temporarily associated with the lipid bilayer or with integral proteins through weak noncovalent interactions)
what are most integral membrane proteins
Transmembrane proteins (spanning the entire lipid bilayer)
Explain the different regions of transmembrane proteins on a receptor
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
What do peripheral membrane proteins do
- 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
what is used to demonstrate protein mobility
fluorescence recovery after bleaching FRAP
What is homeostasis
the active maintenance of a stable environment within cells and organisms, done by the cell membrane and organelles
how does the cell membrane maintain homeostasis
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
how is it selectively permeable
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
What is simple diffusion
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)
what is facilitated diffusion
molecules move passively down concentration gradient through protein transporters
What are the two types of membrane transporters (proteins)
- 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)
- Carrier proteins - bind to and then transport molecules. the membrane protein will change shape during the transportation of the molecule.
how does water move through the membrane
mainly passively (due to molecules being small enough) through the bilayer by means of simple diffusion. also by channel proteins called aquaporins (facilitated diffusion)
Explain osmosis
Movement of water from regions of high water concentration to lower water concentration, or from regions of lower solute concentrations to higher solute concentrations
What is active transport
the movement of molecules from low to high concentration gradient. requiring a form of input energy
How can osmosis be prevented
by applying force to the apartment with higher solute concentration, decreasing osmotic pressure
how does the membrane move substances during active transport
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
example pf active transport pump
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)
what are antiporters & symporters
transport proteins that transport substances in opposite directions
& proteins that move substances in the same direction
What is secondary active transport
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
Example of secondary active transport
Proton (H+) pump
What direction do these charged molecules move in
from an area of like charges to unlike charge
describe the movement of protons
always from regions of higher to lower concentration
Explain the difference in the following solutions:
1. Isotonic
2. Hypotonic
3. Hypertonic
- the outside water concentration = the same as the inside
- the outside water/solute concentration is lower than the inside (contractile vacuoles)
- the outside water/solute concentration is higher than the inside
what are co-transporters
the coupling of the favourable movement (with its concentration gradient) of one molecule, with the unfavourable movement (against its concentration gradient) of another molecule
