Chapter 4: Cell Structure and Membranes Flashcards
Cell theory, developed in the 19th century, has 3 components. List the components.
- Cells are the fundamental units of life
- All living organisms are composed of cells
- All cells come from pre existing cells
What is the cytoplasm?
Jelly-like fluid that makes up the space between organelles
What is the cell membrane?
The cell membrane is the outermost edge of the cell.
- cell membranes separate the internal environment from the external environment, giving cells or cell compartments the ability to regulate their internal composition.
- enables the transfer of several molecules such as nutrients and hormones in and out of the cell
- having receptors for different hormones, neurotransmitters, and proteins to bind to in order to elicit a cellular response. This means that the cell can respond to external stimuli
What are internal/organellar membranes? What is their purpose? What is the difference between eukaryotic and prokaryotic cells?
Membranes that divide the internal space intro discrete compartments to segregate processes and components(ex. mitochondria, nucleus, Golgi apparatus).
All organelles in eukaryotic cells are enclosed by a membrane. Organelles in prokaryotic cells are not.
Cell and organelle membranes are composed of two layers - ______________(1).
(1) Lipid bilayers
___________________(1) describes the extent of lateral movement of lipids and proteins in the membrane. Lipids and proteins are _________________(2). Phospholipids can move ____________________(3).
(1) Membrane fluidity
(2) not stationary
(3) Laterally (side to side)
- Called lateral diffusion
What 3 factors influence membrane fluidity?
- Lipid composition: Short, unsaturated chains increase fluidity
- Temperature: Fluidity decreases I cold conditions; some organisms alter lipid composition in cold environments.
- Cholesterol content: Alters interactions among fatty acid side chains
What is cholesterol?
Cholesterol is a lipid that is a normal component of many animal cell membranes(both plasm membranes and organelle membranes). It has a largely hydrophobic structure. At body temperature, its presence decreases lateral movement and thus fludiity
Why is membrane fluidity important?
It permits the shape changes that accompany cell growth and movement.
Important during membrane fusions or membrane fissions(ex. cell division)
What does the fluid mosaic model of cell membranes state?
Lipids and proteins move laterally through the membrane.
Phospholipids form ___________(1) with the charged, __________________(2) on the outside and the _____________________________(3) on the inside of the membrane.
(1) bilayers
(2) hydrophilic heads
(3) non polar hydrophobic fatty acid tails
Membrane fluidity can be measured using FRAP. What is FRAP?
Fluorescence recovery after photobleaching(FRAP) is an experimental technique that allows scientists to measure membrane fluidity. Fluorescently-labelled lipids or membrane proteins are “bleached” in a small area of the membrane, and the time need for fluorescence recovery is measured. The relative fluorescence intensity is measured over time
The hydrophobic interior of the phospholipid membrane prevents ___________________________(1).
(1) diffusion of polar molecules and ions through the membrane
What are integral membrane proteins?
- at least partly embedded in phospholipid bilayer
- Hydrophobic regions interact with membrane interior
Hydrophilic regions interact with eh aqueous environment
What are anchored membrane proteins?
Covalently attached to fatty acids or other lipid groups
What are peripheral membrane proteins?
Have no hydrophobic groups, so they only interact with the hydrophilic phospholipid head ON THE SURFACE(can be outside or inside)
- Do not enter the hydrophobic space
- attach to the membrane but not be locke, Not embedded in the bilayer
- polar or charged regions interact with exposed parts of integral membrane proteins or with charged head of phospholipids.
What are transmembrane proteins?
A type of integral membrane protein that crosses the entire length of the bilayer membrane.
May have domains with different functions on the inner and outer sides of the membrane
- Transmembrane domains(segments that are between the bilayer) are hydrophobic and contain largely non polar amino acid side chains.
- Polar and charged amino acid side chains(hydrophilic) are exposed outside the bilayer, interact with aqueous environemnts
What role do carbohydrate on the outer cell membrane play?
Communication and adhesion
What is a glycolipid?
Carbohydrate attached to a lipid
What is a glycoprotein?
oligosaccharide (containing a small number of monosaccharides, 3-10) attached to a protein
What is proteoglycan?
Longer carbohydrate attached to a protein
What are the three main biological function of membranes?
- Form specialized compartments: Because membranes are selectively permeable, they retain certain compound with ions within cells and within specific cellular compartments, while excluding others
- Act as a selective filter: Transporters(proteins) allow entry of nutrients and excrete metabolic waste
- Communication with cell’s surroundings: Receptors sense extracellular signals and trigger molecular changes in the cell
What is selective permeability?
Biological membranes allow some substances, but not others, to pass
What is passive transport?
Passive transport does not require energy; substances diffuse down a concentration gradient
Energy is released as it is a spontaneous process. Concentration gradients are a source of stored energy for cells
What is active transport?
Active transport requires energy and the assistance of specialized membrane proteins
Substances are moved against a concentration and/or electrical gradient
Often facilitated by proteins called transport pumps
What are the two types of passive transport?
Simple diffusion: Which occurs unassisted across the phospholipid bilayer, ex. non polar substances
Facilitated diffusion: Occurs with the help of transport proteins
What is osmosis?
The diffusion of water across semipermeable membranes. It applies to cases where a membrane is permeable to water, but isNOT permeable to a solute(a dissolve substance such as glucose)
- Water will always move passively and spontaneously from low solute concentration to high solute concentration
- Water moves with SIMPLE DIFFUSION
- Rapid transport of water requires the help of channel proteins called aquaporins. This is an example of facilitated diffusion
Always check to see if the question is asking for JUST water movement or NET water movement
REMEMBER THIS LOLL
Concentration gradients can exist for both __________________ and _______________.
cocnentraitona dn charge
The hypertonic area is the __________?
More concentrated area
Hypotonic is area of lower concentration
Cells must keep intra and extracellular solutions close to ____________(1).
(1) isotonic
What does the speed of diffusion depend on?
- Diameter of molecules
- Temperature
- Concentration gradient
- Area and distance
What is diffusion?
The random movement of particles toward a state of equilibrium; a net movement from regions of higher concentration to regions of lower concentration
In a complex solutions(with many different solutes), diffusion of each solute depends only on ______________(1).
(1) its own concentration
What is simple diffusion? Which molecules can pass through?
O2, CO2, and small, non polar lipid soluble(can dissolve in fats, oils, fatty tissues) molecules can cross the membrane unaided. Water and urea can also pass but permeability is lower
What is facilitated diffusion?
Passive transport of solutes down their concentration gradient with the help of integral transmembrane proteins
What are channel proteins?
Form channels across the membrane
- contain a pore via which ions may cross from one side of the membrane to the other(also known as ion channels)
- In ion channels, water can “hitchhike” along with some ions - not used in active transport
- much faster rate of transport than carrier proteins
What are aquaporins?
Channels for movement of water
What are carrier proteins?
Bind to a polar molecules and solutes to speed up diffusion
- bind a solute and undergo a change in shape to translocate the solute across the membrane
- only bind a specific molecule via an attachment similar to an enzyme-substrate interaction
- also used in active transport
Examples: glucose or amino acid transporters
What is a lipoprotein?
Lipoproteins carry cholesterol and triglycerides to cells in your body.
Glucose is quickly broken down in the cell. What implication does this have?
There is always a strong concentration gradient that favours glucose uptake.
The system can become saturated- when all of the carrier molecules are bound, the rate of diffusion reaches a maximum
What is uniport?
One type of solute molecule is transported
What is symport?
Two types of solute molecules are transported in the same direction
What is antiport?
Two types of solute molecules are transported in the opposite direction
What are the two main types of active transport?
- Primary active transport: involves hydrolysis of ATP for energy
- Secondary active transport: Uses the energy that is stored in an ion concentration gradient, which are established by primary active transport
An example of primary active transport is the _______________(1). One molecule of ATP moves ___(2) K+ and ___(3) Na+ ions. This maintain _______(4) at a higher concentration inside the cell and ________(5) at a higher concentration outside the cell.
(1) sodium-potassium pump
(2) 2
(3) 3
(4) K+
(5) Na+
The Na+ - K+ pump establishes a concentration gradient of ___(1), then passive diffusion of _____(2) back into the cell provides energy for _______________(3)
(1) Na+
(2) Na+
(3) Glucose transport
In secondary active transport, one protein usually moves both the ______(1) and the ___________________(2) across the membrane. This is known as ______________________(3)
(1) ion
(2) transported molecule
(3) coupled transport or co-transport
Explain the correlation between a defective ion channel and cystic fibrosis.
The normal transmembrane protein is an ion channel specific for Cl- ions. Cystic fibrosis is caused by defects in CFTR, which impairs the transport of chloride ions and the movement of water into and out of the cell, resulting in a thick mucus.
Most ion channels are gated channels. What does this mean? What are the two types of gated channels?
Gated channels open when a stimulus causes the protein to change shape.
Ligand gated - the stimulus is a ligand, a chemical signal
Voltage gated - the stimulus is a chance in electrical charge difference across the membrane
What is the secretory pathway?
rough ER, Golgi apparatus, vesicle, plasma membrane
What does the rough ER do in the secretory pathway?
produce proteins for the rest of the cell to function.
What does the Golgi do in the secretory pathway?
Chemically modifies protein and sorts them for transport to their final destinations
What are the three types of cell junctions that join animal cells?
- Tight junction: prevent substances from moving through spaces between cells
- Desmosomes: Hold cells together with stable protein connections; provide stability for tissues such as skin
- Gap junctions: channels that run between membrane pores; allow materials and electrical signals to pass
What are the 4 functions of the cytoskeleton?
- Supports and maintains cell shape
- Maintains position of organelles and other particles within the clel
- Move organelles and other particles within the cell
- Interacts with extracellular structures to anchor cell in place
What is pinocytosis? What is phagocytosis?
Vesicles are smaller and bring in fluids and dissolved substances
Phago: eating
What is receptor mediated endocytosis?
Brings specific large molecules into a cell via specific receptors
What is a vesicle?
A carrier made of lipid, vesicles can fuse with or for from membranes
