Cells Flashcards
Define cell
the basic living, structural, and functional units of all organisms
What are the main components of cell theory?
1.) if it’s not made of cells, it’s not living; 2.) the activity of cells is a result of both individual and aggregated cells; 3.) function of a cell is determined by its composition
What is the Principle of Complementarity?
1.) cells are responsible for the continuity of life; 2.) cells come from other cells
What are the 3 main parts of a cell?
plasma membrane, organelles, cytoplasm
What two distinct parts make up the phospholipid bilayer?
phosphate heads and fatty acid (lipid) tails
Which part of the phospholipid bilayer is polar? Which is nonpolar?
The heads are polar and the tails are nonpolar (the tails are lipids, which cannot dissolve in water)
Which part of the phospholipid bilayer is hydrophobic? Hydrophilic?
the fatty acids are hydrophobic (nonpolar); the phosphate heads are hydrophilic (polar)
What is it called when something contains parts that are both hydrophilic and hydrophobic?
amphipathic
Besides the phospholipid bilayer, what 4 other parts can be found on the plasma membrane?
integral proteins, peripheral proteins, glycoproteins, and cholesterol
What 6 activities are carried out by membrane proteins?
transport, receptors for signal transduction, enzymatic activity, cell-cell recognition, attachment to the cytoskeleton and extracellular matrix, and cell-to-cell joining
What are integral proteins?
proteins that are firmly inserted into the lipid bilayer (most are transmembrane proteins that protrude on both sides of the bilayer
What activities are integral proteins responsible for?
transport, carriers, enzymes, signal transduction
What is a peripheral protein?
a protein that is only found on one side of the phospholipid bilayer - usually toward the inside
What activities are peripheral proteins responsible for?
help with membrane structural support, some are enzymes, some are mechanical proteins that help during cell division, muscle cell contraction, etc.
What are glycoproteins made of?
carbohydrates
Why is it important for a plasma membrane to have cholesterol on it?
the cholesterol acts as a glue that holds together all the moving parts
What is a phrase that describes the image of a plasma membrane?
fluid mosaic
Why is “fluid mosaic” a good term to describe the plasma membrane?
mosaic = different parts; fluid = movement
What are 4 important functions of a plasma membrane?
limiting boundary, first point of contact for the cell, provides receptor sites, and controls flow of what goes in and out of cell (LCRF - lacroff)
What are the four factors that determine whether or not something will be permitted to cross the plasma membrane?
molecular size, solubility, ionic charge, and carrier molecules (mmsc - not musc)
Why is size important in determining whether or not something can cross the plasma membrane?
small things can cross better than bigger things
Why is solubility important in determining whether or not something can cross the plasma membrane?
anything that is nonpolar can cross the membrane easily (ex: lipids are fats so they can be dissolved and travel easily through any of the proteins located throughout the membrane)
Why is ionic charge important in determining whether or not something can cross the plasma membrane?
ionic substances are polar so they must move through proteins to get across (charges must be opposite in order to cross)
How are active and passive transport different?
active transport requires energy in order to work and moves against the concentration gradient; passive transport does not require energy to work and moves with the concentration gradient
Name the four types of passive transport
diffusion, facilitated diffusion, osmosis, and filtration (doff)
Explain diffusion
Molecules move from areas of high concentration to areas of low concentration until equilibrium is reached
What three factors can affect the rate of diffusion?
concentration, molecular size, temperature
Why does concentration affect the rate of diffusion?
if there are more molecules present, there is a higher chance of collisions happening and the rate of diffusion will be faster
Why is temperature important in determining the rate of diffusion?
higher temperatures mean molecules will be moving at higher speeds
Why is size important in determining rate of diffusion?
smaller molecules can move quicker than larger molecules
Explain simple diffusion
substances can diffuse directly through the lipid bilayer if they are 1.) small enough, and 2.) lipid soluble (ex: gases, steroid hormones, fatty acids)
What is facilitated diffusion? What are the 2 types?
molecules are transported across the phospholipid bilayer with a little help; two types: carrier-mediated facilitated diffusion, channel-mediated facilitated diffusion
What types of molecules utilize facilitated diffusion?
glucose and other sugars, some amino acids, ions
Explain carrier-mediated facilitated diffusion
a lipid-insoluble molecule must past through a transmembrane protein in order to enter the cell; the protein carriers are specific to certain chemicals (ex: sugars, amino acids) and can reach capacity if all are being used; when the solute enters into the protein, the protein changes its shape to be able to pass the solute to the other side
Explain channel-mediated facilitated diffusion
transmembrane proteins act as channels in which substances can cross freely; the type of substance that can travel through these proteins is determined by channel size and the kinds of amino acids lining the channels; some channels are “gated” while others are always open
What types of substances would enter a cell through facilitated diffusion?
water, ions, glucose - if energy were required for these to pass, our bodies would be using wayyy too much ATP!
Explain osmosis
the diffusion of water across a selectively permeable membrane; water always moves from low concentrations to high concentration
Which direction does water move across a gradient?
water flows from low concentration to high concentration
Define osmolarity
the number of charged particles that determine the flow of water (low –> high)
Explain filtration
the movement across a selectively permeable membrane due to pressure (think of a coffee filter using gravity)
What is tonicity?
the ability of a solution to change the shape of cells by altering the cell’s internal water volume
What are the 3 types of tonicity a cell can experience?
isotonic, hypertonic, hypotonic
Describe an isotonic cell
solutions have the same concentrations; cells retain their shape
Describe a hypertonic solution
the solution has a higher concentration outside the cell than inside the cell (hyper outside); cells immersed in hypertonic solutions will lose water (low –> high) and crenate (shrive)
Describe hypotonic
more dilute solution than the cell (the concentration inside the cell is greater than outside of it); water will flow into the cell (low –> high), and the cell will lyse (burst)
T/F: Water always moves from hypertonic to hypotonic
False; water moves from hypotonic to hypertonic because it always moves from low to high!
What is the energy source for passive transport?
kinetic energy
What are three reasons why active processes might need to be used?
substance is 1.) too large, 2.) incapable of dissolving in lipid bilayer, 3.) moving against concentration gradient
Explain how a Sodium Potassium pump works
a protein contains 3 binding sites for sodium; when the sodium is attached, a phosphate also binds to the pump; when the phosphate binds, this causes the pump to change shape and the sodium can be released to the other side; now open for business on the other side, 2 potassium can bind to the protein; the binding of the potassium triggers the attached phosphate to leave and the protein can revert back to its original shape; to remove the potassium from the protein, ATP is needed and the pump can go back to the beginning of the cycle
Explain secondary active transport
uhhhh
What is vesicular transport?
a form of active transport where the particle in question is moved across the membrane in a large bubble-like sac, called a vesicle
What are the two main types of vesicular transport?
endocytosis and exocytosis
Explain exocytosis
something that needs to be moved out of a cell is encased in a sac; this sac migrates to the plasma membrane, fuses with it, then ruptures, dispelling the substance in question
What are examples of substances that are expelled using exocytosis?
hormones, neurotransmitters, mucus, waste
What are the 3 main types of endocytosis?
phagocytosis, pinocytosis, and receptor-mediated cytosis
Define endocytosis
moving things into a cell that either weren’t allowed entry via passive transport, or could not get in via primary or secondary active transport (pumps/K+ and Na+ reactions)
Explain phagocytosis
similar to the idea of Pac-Man - the cell engulfs its target and draws it into the cell; relatively rare in our bodies (only macrophages and white blood cells can do it)
What are situations when phagocytosis is used?
disposal of dying cells, ingesting bacteria and foreign substances
Explain pinocytosis
the cell “gulps in” the particle in question; relatively common in our bodies; “cell drinking”
Explain receptor-mediated endocytosis
the substance in question binds to specific receptor proteins located on the cell and “pull” the substance inside a vesicle to enter the cell
What are some cases where receptor-mediated endocytosis is used?
enzymes, insulin and other hormones, low-density lipoproteins, and iron; but also flu virus, diphtheria, and cholera toxins
What is clathrin?
protein coating on cytoplasmic face of vesicle
What is the resting membrane potential?
a voltage across the membrane caused by K+ leaking out of the cell through transmembrane proteins until there is such a negative pull from inside the cell that the K+ starts to get pulled back in; in a normal cell between -50 and 90mV (typically about -70mV because of Na+)
What are the two types of cellular extensions?
cilia and flagella
What does a flagella help to do? Where is it found?
acts as a tail and propels the cell where it needs to go; only found in sperm cells
What do cilia help to do and where can they be found?
whiplike, motile extensions that move substances in once direction across a cell’s surface; can be found in the respiratory tract, other places (ex: propel mucus and dust away from the lungs)
What are microvilli? Where are they found?
extensions of the plasma membrane that increase surface area; often in absorptive cells (intestines, kidneys, etc.)
Describe the mitochondria
“powerhouse of the cell”; can reproduce by itself (contains its own DNA); areas which require lots of energy have high density of mitochondria; enzymes live inside to help with ATP activities
Where are ribosomes found?
free ribosomes: float around in the cytosol; membrane-bound ribosomes: attached to membranes in the rough ER
What do ribosomes do?
“factory floor”; synthesis sites; make proteins; can switch from being free to attached depending on what they are making
What does the rough endoplasmic reticulum do?
houses the ribosomes that make proteins; houses the “membrane factory” where integral proteins and phospholipids are make
What does the smooth endoplasmic reticulum do?
contains many enzymes which help to break down stored glycogen (releasing glucose), detoxify drugs, pesticides, and chemicals, store calcium ions, and produce/synthesize steroid-based hormones and cholesterol and phospholipids
What is the difference between the smooth ER and the rough ER?
rough ER has ribosomes and produces many proteins and membrane-building materials; smooth ER produces steroid hormones, helps with detoxification, and breaks glycogen down into glucose
What is the function of the Golgi Apparatus?
“UPS store”; packs and ships all the lipids and proteins produced by the rough ER
What is a peroxisome?
smaller version of a lysosome; help to detoxify dangerous substances and go after free radicals (like police officers p-p)
Where are peroxisomes often found?
liver and kidneys
What are lysosomes?
“taking out the trash” - dispose of invading bacteria and cell debris often through phagocytosis; work best in acidic environments
What is cytosol?
the liquid part of the cytoskeleton
What is a microtubule?
make up part of the cytoskeleton, determine overall shape of the cell and distribution of organelles; mitochondria, lysosomes, and secretory vesicles hang from them
What are microfilaments?
help to strengthen plasma membrane and give cell mobility to be able to change shape due to the fluidity of its movements
What are intermediate filaments?
most stable of the cytoskeleton elements, act as cables that resist forces pulling on the cell
What are cell junctions and what are the 3 types?
the unique relationships cells have with their neighbors; tight junctions, desmosomes, and gap junctions
What is a tight junction? Where can it be found?
the integral proteins in the plasma membrane fuse together with the integral proteins of other cells to create an impenetrable membrane; prevent molecules from passing through; found in the digestive tract to keep acid from seeping into the blood stream
What are desmosomes? Where can they be found?
also called “anchoring junctions”; act like Velcro where cells are connected into sheets in order to best take strong forces of friction; found in areas where friction could be common (heart muscle, skin)
What are gap junctions? Where can they be found?
channel proteins of two cells fuse together and create a “gap” where things in both cells can easily pass to each other; found in electrically-excitable tissues (heart and smooth muscle)
