Chapter 3: The Cell
what is a cell
it is the structural and functional unit of life
what are the cells 3 basic parts?
1. plasma membrane
what is the plasma membrane? what does it do?
it is the flexible outer boundary. it is composed of a 'lipid bilayer' that has protein molecules plugged into it
it separated the ICF from the ECF
what is the lipid bilayer of the plasma membrane made out of?
phospholipids, glycolipids, cholesterol, and lipid rafts
define the phospholipid of the plasma membrane bilayer
the phospholipids are 75% of the membrane lipids
they have a polar, hydrophilic head
they have a uncharged, non-polar hydrophobic tail
- the polar heads are exposed to the water, while the tails remain inwards
define the glycolipids of the plasma membrane bilayer
the glycolipids account for 5% of the membrane lipids
these are lipids with polar sugar groups on outer membrane surface
define the cholesterol of the plasma membrane bilayer
makes up about 20% of membrane lipids
it has polar and non-polar regions
it increases membrane stability
what are membrane proteins? name the 2 types
the plasma membrane 'bristles' with proteins
these proteins are responsible for most of the specialized membrane functions and they allow communication with the environment
what are integral proteins? what do they function as?
integral proteins are inserted into the membrane
most are 'transmembrane' meaning they span the entire membrane
they have hydrophilic and phobic regions
they function as transport proteins- channels and carries- enzymes and receptors
what are peripheral proteins? what do they function as?
they are loosely attached to integral proteins
they function as enzymes, motor proteins for shape changing during cell division and muscle contraction, they also link cells together
define lipid rafts. what do they function as?
lipid rafts make up 20% of the outer membrane surface
composed of sat. phospholipids, sphingolipids, and cholesterol
they are more stable and less fluid than the rest of the membrane
they function as stable platforms for cell signaling and membrane invagination
what is the glycocalyx?
it is the 'sugar covering' at cell surface - branching sugar groups from glycolipids and glycoproteins
every cell has a different pattern of sugars- these different patterns are biological markers for cell to cell recognition
what are the 3 types of cell junctions? what is a cell junction?
some cells are free, some are bound together- a cell junction binds cells into tight communities
1. tight junctions
3. gap junctions
explain tight junctions
adjacent integral proteins fuse and form impermeable junctions
they prevent molecules from passing through intercellular space
major regulator of permeability
what is IF?
IF is interstitial fluid. it surrounds cells
the plasma membrane allows cells to obtain from IF exactly what it needs when it needs it and keep out what it does not need
explain desmosomes structure
rivets or spot welds that anchor cells together at plaques- or thickened patches
desmosomes contain special proteins such as keratin filaments that extend to the opposite plaques which reduce possibility of tearing and gives stability to the cell
explain desmosomes function
they bind adjacent cells together like a molecular "velcro" and help form an internal tension-reducing network of fibers
can be found in muscle tissue where they bind muscles together
explain gap junctions structure
in gap junctions 2 cells are separated from a small gap that is bridged by special channels that allow passage of water and other small molecules
*for spread of ions, simple sugars and other small molecules between cardiac or smooth muscle cells
explain gap junctions function
communicating junctions allow ions and small molecules to pass for intercellular communication
explain plasma membrane transport. what are the 2 types?
the plasma membrane is selectively permeable meaning some molecules can pass through easily while others can not.
the 2 types are
what are the 2 types of passive transport?
what are the 2 types of passive transport? what are the different types of diffusion?
the 2 types of passive transport are diffusion and filtration.
the different types of diffusion are
2. carrier/ channel mediated
what is diffusion?
this is when collisions cause molecules to move down or with their concentrations gradient
the speed is influenced by molecule size and temperature
when will a molecule passively diffuse through a membrane?
if it is
1. lipid soluble
2. small enough to pass through membrane channel
3. assisted by carrier molecule
explain simple diffusion
nonpolar and lipid soluble substances diffuse directly through phospholipid bilayer
i.e. oxygen, carbon dioxide, fat-soluble vitamins
explain facilitated diffusion
certain lipophobic molecules (glucose, amino acids) are transported passively by facilitated diffusions where
1. the substance binds to protein carriers in the membrane
2. or the substance moves through water filled protein channels
explain carrier-mediated facilitated diffusion
carriers are transmembrane integral proteins that are specific for transporting certain molecules too large for channels
alterations in the shape of the carrier allow it to first envelope and then release the transported substance
explain channel-mediated facilitate diffusion. what are the 2 types?
channels are transmembrane proteins that transport substances through aqueous channels from one side of the membrane to the other
channels are selective due to pore size and the charges of the amino acids lining the channel
selectively transport ions or water
the 2 types are
1. leakage channels: always open
2. gated channels: controlled by electrical/ chemical signals
the movement of solvent across a selective permeable membrane- i.e. water
water diffuses through the plasma membranes
1. through the lipid bilayer
2. through specific water channels called aquaporins (AQPs)
when does osmosis occurs?
it occurs whenever the water concentration differs on the two sides of a membrane
water moves by osmosis until hydrostatic pressure and osmotic pressure equalize
measure of total concentration of solute particles in a solution
what is the importance of osmosis?
it causes cells to swell and shrink
the change in cell volume disrupts cell function, especially in neurons so osmosis is vital
define tonicity. what are the 3 types?
tonicity is the ability of a solution to change the shape or tone of cells by altering cell's water volume
define isotonic solutions
isotonic is a solution with the same non-penetrating solute concentration as cystol
.9% saline or 5% glucose
cells exposed retain their normal shape and size
define hypertonic solutions
have a higher concentration of non-penetrating solutes than seen in the cell
they lose water and shrink or 'crenate'
define hypotonic solutions
contain a lower concentration of solutes than cells
cells plump up rapidly or burst- 'lyse', when in this type of solution because water rushes into them
i.e. distille water
name the different types of passive transport and give examples of what they move
1. simple diffusion: fat, oxygen, carbon dioxide
2. facilitated: glucose and some ions
3. osmosis: water
what is active transport? what are the 2 types?
active transport is any type of transport that uses energy to move solutes across a membrane
what is active transport? (type 1)
active transport requires carrier proteins like facilitated diffusion- however facilitate diffusion always moves with the concentration gradient - in contrast active transporters or 'solute pumps' move solutes uphill and against concentration gradient
what are the 2 types of active transport? explain
1. primary: the energy to do work comes directly from the hydrolysis of ATP
2. secondary: gets energy from stored ionic gradients created by primary active transports
explain primary active transport
energy from hydrolysis of ATP causes shape change in transport protein that pumps solutes across membrane
explain secondary active transport
uses stored energy from ionic gradients that are created by primary active transport
secondary transport are 'coupled systems' or 'contransport' meaning they always transport more than one substance at a time
symport system- substance transported in same direction
antiport- substance transported in opposite directions
explain vesicular transport
the transport of large particles, macromolecules, and fluids across the membrane in membranous sacs called vesicles
vesicular transport: define the following
4. vesicular trafficking
1. movement into a cell
2. movement out of a cell
3. movement of substance into, across and then out of a cell
4. moving substances from one area to another
what does vesicular transport always involve?
1. protein-coated vesicles
2. membrane receptors that mediate
"cell eating" - your a phag so you eat a lot"
pseudopods engulf solids and bring them into cells interior
used by macrophanges and some white blood cells
most move by amoeboid motion
receptors are used
fluid- phase endocytosis- "think pinot wine"
plasma membrane infolds, bringing extracellular fluid and dissolved solutes inside cell
this type of endocytosis is a routine activity of most cells- especially nutrient absorbing ones
no receptors are used. so the process is nonspecific
receptor mediated endocytosis
extracellular substances bind to specific receptor proteins, enabling the cell to ingest and concentrate specific substances in protein coated vesicles. receptors are recycles to the plasma membrane in vesicles
selective mechanism for endocytosis and transcytosis
clarithin coated pits provide the main route for endocytosis and transcytosis
name the coat proteins for receptor mediated endocytosis
1. clarithin coated pits: enzymes, low density lipoproteins, iron, insulin, viruses, and cholera toxins
2. caveolae: capture specific molecules sand use transcytosis
process of ejecting substances from the cells interior to the extracellular fluid
usually triggered by the binding of a hormone or a change in membrane voltage
exocytosis accounts for hormone secretion, neurotransmitter release, mucus secretion and ejection of wastes sometimes
v-snares bind with t-snares
v-snares= transmembrane proteins
t-snares= plasma membrane proteins
the plasma membrane and resting potential
all body plasma membranes have a RP of -50-100 mV, which is a voltage across the membrane
so all cells are said to be polarized; the negative sign indicates that the inside of the cell is negative compared to the outside
this charge only exists at the membrane
how is RP created? and how is it maintained?
created: diffusion causes ionic imbalances that polarize the membrane
maintained: active transport processes
selective diffusion establishes RMP
what are the bases of DNA?
what are the bases in RNA?
where does cell division NOT occur?
nervous tissue, cardiac muscle, skeletal muscle
role of RNA
it is a DNA decoding mechanism and messenger
there are 3 types; mRNA, rRNA, tRNA