Chapter 3: The Cell

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what is a cell

it is the structural and functional unit of life


what are the cells 3 basic parts?

1. plasma membrane
2. cytoplasm
3. nucleus


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

1. integral
2. peripheral


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

there are
1. tight junctions
2. desmosomes
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
1. active
2. passive


what are the 2 types of passive transport?

1. diffusion
2. filtration


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
1. simple
2. carrier/ channel mediated
3. osmosis


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


explain osmosis

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

1. isotonic
2. hypertonic
3. hypotonic


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

1. active
2. vesicular


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

requires ATP


vesicular transport: define the following

1. endocytosis
2. exocytosis
3. transcytosis
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


explain phagocytosis

"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


explain pinocytosis

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


exocytosis process

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