A&P - Chapter 3: Cell Biology

what is the plasma membrane

AKA cell membrane

lipid bilayer that forms the outer boundary of the cell

plasma membrane structure

lipid bilayer

• phospholipids and cholesterol

  • phosphate (head) is hydrophilic, so it remains on the outside, while the fatty acid (tail) is hydrophobic (and nonpolar), so they remain on the inside, away from water

has proteins in it or attached to the outside

plasma membrane function

outer boundary of the cell

controls the entry and exit of substances

• semi-permeable barrier

• makes sure organelles do not leave

intercellular communication

cell recognition

attaches to the extracellular environment / other cells

maintains homeostasis of the cell

creates different membrane potentials

membrane potential

The result of the cell’s regulation of ion movement in and out of the cell

can be electrical + chemical potentials

• At rest, the membrane potential is negative on the inside

electric potential

difference in ion charges on both sides of the membrane

• EX: if K+ ions leave the cell, the inside of the cell is more negative while the outside is more positive

chemical potential

difference in ion concentrations

• EX: if K+ leaves the cell, there is MORE K+ ions on the outside of the cell and less on the inside of the cell.

glycocalyx

collection of glycolipids, glycoproteins, and carbohydrates on the outer surface of membrane

also contains molecules absorbed from extracellular environment

plasma membrane lipids

two main types:

1. phospholipid

2. cholesterol

phospholipid

create the lipid bilayer

have polar heads — hydrophilic

• remain on the outside of the membrane and interact with aqueous solutions

have nonpolar fatty acid tails — hydrophobic

• remain facing one another on the inside of the membrane

fluid-mosaic model

describes PM as flexible

• helps distribute molecules within plasma membrane

• damage to the membrane can be fixed because phospholipids can reassemble in damaged sites

• enables membranes to fuse with one another

cholesterol

fewer than phospholipids

determines fluid nature of membrane

• limits movements of phospholipids

• provides stability to PM

integral vs peripheral membrane proteins

integral: proteins that penetrate into bilayer

• can extend from one surface to another

• does so with hydrophobic R groups

peripheral: attached at either inner or outer surface of bilayer

marker protein

cell surface molecule

can be both integral and peripheral

key for cell identification

mostly glycoproteins or glycolipids

attachment protein

integral protein

allows cells to attach to other cells / extracellular molecules

• EX: cadherins and integrins

cadherin

proteins that attach to other CELLS

integrin

proteins that attach cells to extracellular molecules

functions in pairs of integral membrane proteins that interact with both cytoplasmic + extracellular molecules

also function in cellular communication

transport proteins

integral proteins

allow ions/molecules to move from one side of PM to another

3 important characteristics:

1. specificty

2. competition

3. saturation

3 major classes:

1. channel proteins

2. carrier proteins

3. ATP-powered pumps

specificity - transport proteins

each transport protein binds to and transports only a certain type of molecule or ion

• EX: a channel that transports glucose cannot transport amino acids

  • determined by shape of binding site

    • only glucose matches binding site shape which allowed it to pass through

competition - transport proteins

result of molecules with similar shape binding to transport protein

substance with greater concentration OR substance that binds to binding site faster will move across membrane at a greater rate

saturation - transport protein

rate of movement of molecules across membrane is limited by number of available transport proteins

channel proteins

made up of integral proteins

go through the plasma membrane

ions / small molecules of the right size + charge can pass through

• charge in the hydrophilic part of protein determines passage

two types:

1. leak ion channels

2. gated ion channels

leak ion channels

always open

responsible for PM permeability to ions when at rest

gated ion channels

open and close depending on stimuli

• chemical signals

  • ligand binding to ion channel —> ligand-gated ion channel

• change in membrane potential

  • voltage-gated ion channels

vital to homeostasis

exhibit specificity, competition, and saturation

carrier proteins

AKA transporters

integral membrane proteins

molecule attaches to the binding site within carrier protein —> carrier protien changes shape + takes molecule to the other side of the membrane

• can transport one ion/molecule at a time

• can transport more than one type of substance at a time

three classifications:

1. uniport

2. symport

3. antiport

uniport

movement of one specific ion/molecule across the membrane

uniporter carrier protien

symport

movement of two different ions/molecules in the same direction across the membrane

AKA contrasport

symporter carrier protein

antiport

movement of two different ion/molecules in opposite directions across the membrane

AKA contertransport

antiporter carrier protien

ATP-powered pump

transport protein that requires energy to move ions/molecules across membrane

fueled by the breakdown of ATP (adenosine triphosphate) into ADP (adenosine diphosphate)

has binding sites for specific ions/molecules + binding site for ATP

when ATP —> ADP energy is released which changes shape of the pump and transports the ion/molecule across the membrane

receptor protein

membrane proteins / glycoproteins

have exposed receptor sites

chemical signals can attach to these sites

• important for cellular communication for bodily functions

  • one cell releases a chemical signal which binds to another cells receptor site

    • signal only works for the specific receptor site it was made for

there are receptors linked to channel proteins and receptors coupled to G protein complexes

drugs can inhibit or activate actions of receptors due to similar shapes to the receptor site

receptors linked to channel proteins

receptors that help form ligand-gated ion channels that span the membrane

chemical signals/ligands bind to receptors, the channel changes shape which causes the gate to open or close

receptors coupled to G-protein complexes

g protein is an intermediary between receptors and other cellular proteins

3 proteins involved in g protein:

1. alpha (α)

2. beta(β)

3. gamma (γ)

process of g proteins + receptors

1. g protein not interacting with a receptor has GDP (guanoside diphosphate) attached to alpha subunit

2. chemical signal binds to receptor, alpha subunit releases GDP and attaches to GTP

• this makes alpha subunit active

3. g protein complex separates from receptor + alpha subunit separates from beta and gamma subunits

4. the alpha subunit can stimulate cell response in different ways

• opening ion channels

• by means of intracellular chemical signals

• activation of enzymes

enzymes

membrane protein

can catalyze (speed up) chemical reactions on either inner or outer surface of membrane

can always be active OR activated by membrane-bound receptors or G protein complexes

what + how can certain molecules/ions pass through the membrane

O₂, CO₂ , steroids —> dissolve into lipid bilayer to pass through (NO assistance)

small, non-lipid-soluble molecules —> diffuse between phospholipid molecules (NO assistance)

large, non-lipid soluble molecules / ions —> transport proteins

large, non-lipid soluble molecules / small pieces of matter —> vesicles (small membrane-bound sac)

types of membrane transport mechanisms

passive transport

1. diffusion

2. osmosis

3. facilitated diffusion

active transport

1. active transport

2. secondary active transport

3. endocytosis

4. exocytosis

passive transport

does not require the use of ATP to function

diffusion

passive

net movement from high —> low concentration of solute

lipid-soluble molecules

• EX: O₂, CO₂, lipids

factors that influence rate of diffusion

1. magnitude of concentration gradient

• greater concentration gradient —> greater movement of solute particles

2. temperature

• higher the temp —> faster speed the molecules move

3. size of molecules

• smaller molecules diffuse faster

4. viscosity (measure of flow resistance)

• low viscosity = easier flow + faster diffusion

• high viscosity = flows less easily + slower diffusion

solution

consists of one or more substances dissolved in liquid or gas

solvent

the liquid or gas in a solution

when talking about cells —> water is solvent

solute

the substances dissolved in the solvent

when talking about cells —> varies

concentration gradient

difference in the amount of a substance between two areas

• high concentration = lots of particles

• low concentration = fewer particles

solutes diffuse down the gradient until equilibrium is reached

the greater the gradient the greater the rate of diffusion

osmosis

The diffusion of water across a semipermeable membrane

• water can diffuse through the membrane, but not all the solutes dissolved in it can

water diffuses from where there is more water (fewer solutes) to where there is less water (more solutes)

important because volume changes caused by water movement disrupt normal cell function

osmotic pressure

force required to prevent water from moving by osmosis across selectively permeable membrane

three kinds:

1. isosmotic

2. hyperosmotic

3. hyposmotic

isosmotic

solutions with the same concentration of solute particles + the same osmotic pressure

if cell does not shrink or swell when placed into a solution, the solution is isotonic

• cell shape remains constant —> internal tension is maintained (tonicity)

hyperosmotic

when one solution has a greater concentration of solute particles + greater osmotic pressure than another solution

if cell shrinks when placed into a solution, the solution is hypertonic

• water moves out of the cell

• AKA crenation in red blood cells

hyposmotic

the more diluted solution + lower osmotic pressure in comparison to the hyperosmotic solution

if cell grows when placed into a solution, the solution is hypotonic

• water enters the cell

• if cell bursts = process called lysis

facilitated diffusion

mediated transport process

moves substances from a higher to a lower concentration

• carrier proteins

• channel proteins

does not require metabolic energy to function

rate of transportation is proportional to concentration gradient

active transport

requires energy —> ATP

maximum rate at which active transport proceeds depends on # of ATP pumps AND availability of ATP

can move substances AGAINST concentration gradient

• lower to higher concentration

can also move substances down the gradient

• high to low

secondary active transport

when a cell uses the energy stored in a concentration gradient to move another substance across the membrane

EX:

• Sodium (Na⁺) moves high → low.

• Glucose gets carried low → high along with it.

• The transport protein uses the energy from sodium's movement to bring glucose into the cell.

*one substance goes down the gradient to help another one go up.

vesicular transport

movement of larger volumes of substances across the membrane via formation/release of vesicles

• endocytosis

• exocytosis

requires ATP = active membrane transport process

is not as substance specific as other transport processes

endocytosis

material moving INTO the cell via vesicle

• phagocytosis

• pinocytosis

has specificity

phagocytosis

AKA cell eating

solid particles are ingested and phagocytic vesicles are formed

important for eliminating harmful substances from the body

has specificity —> does not phagocytize healthy cells

pinocytosis

AKA cell drinking

smaller vesicles are formed and contain molecules dissolved in liquid instead of particles

common form of transport in a variety of cells

receptor-mediated endocytosis

plasma membrane has specific receptor molecules that recognize certain substances and allow them to be transported into cell by phagocytosis or pinocytosis

increases the rate at which cells take up certain substances

exocytosis

release materials outside of cell (think exhale)

EX: secretion of digestive enzymes

transcytosis

when a substance enters the cell via endocytosis and is moved to the opposite side of the cell and is released via exocytosis.

nucleus

the “brain” of the cells

largest organelle + located at the center of the cell

• some cells lose their nucleus (red blood cells)

• some cells have multiple nuclei (skeletal muscles)

consists of nucleoplasm surrounded by nuclear envelope

nucleus structure

enclosed by a nuclear envelope

has nucleoplasm (cytoplasm of nuclear envelope)

has a double membrane with nuclear pores

holds chromatin (DNA)

• later condensed to form a compact chromosome

nucleosomes

structural units of chromosomes

consists of DNA wrapped around proteins (histones)

DNA in cells

located in nucleus

determines structural and functional characteristics of cell by specifying the structure of proteins

directs protein synthesis by means of intermediate RNA (ribonucleic acid)

three types of RNA important to protein synthesis

1. messenger RNA (mRNA)

2. ribosomal RNA (rRNA)

3. transfer RNA (tRNA)

nucleolis

dense region within nucleus

lacks surrounding membrane

function of nucleus

control center of the cell

DNA inside regulates protein synthesis + chemical reactions of the cell

cytoplasm

Intracellular fluid inside the cell

50% is cytosol

50% is organelles

cytosol

fluid portion of cytoplasm

colloid (viscous solution containing dissolved ions/molecules)

• contains proteins that catalyze breakdown of molecules for energy or synthesis of molecules

other proteins make up cytoskeleton + cytoplasmic inclusions

cytoskeleton

supports cell + holds nucleus and other organelles in place

responsible for changes in cell shape + movement of organelles

consists of three groups of proteins:

1. microtubules

2. actin filaments

3. intermediate filaments

microtubules

hollow tubes made out of a protein called tubulin

help provide support + structure to cytoplasm

involved in cell division and transport of intracellular materials

essential to the formation of centrioles, spindle fibers, cilia, and flagella

actin filaments

AKA microfilaments

form bundles, sheets, or networks in cytoplasm

provides structure to cytoplasm and mechanical support for microvilli

support plasma membrane + define cell shape

• changes in cell shape is caused by the breakdown + reconstruction of actin filaments

  • change in shape can help cells move around

intermediate filaments

protein fibers

provide mechanical support to cells

cytoplasmic inclusions

aggregates of chemicals either produced or taken in by the cell

NOT organelles

• EX: melanin, lipid droplets, crystals, dust, etc

lipochromes

any pigments that increase in amount with age

ribosomes

site for protein synthesis

composed of one large + small subunit that consists of rRNA

can be found free in cytoplasm

• synthesizes proteins used inside the cell

can be found on the rough ER

• produces integral membrane proteins + proteins secreted from the cell

functions of a cell

1. cell metabolism + energy use

2. synthesis of molecules

3. communication

4. reproduction + inheritance

function of a cell - metabolism + energy use

all chemical reactions within a cell

• involves energy transfer

  • Energy released in one reaction is used to start another

  • heat is released

    • good for maintaining body temp

function of a cell - synthesis of molecules

Different cells synthesize different molecules

• proteins

• nucleic acids

• lipids

the strucutral and functional characteristics of cells are determined by the types of molecules they produce

function of a cell - communication

using chemical and electrical signals

function of a cell - reproduction/inheritance

each cell contains complete copy of DNA

• DNA determines structural + functional characteristics of cell

inheritance: transmission of traits from one generation to the next via gametes

ribosome function

site of protein synthesis

ribosome structure

ribosomal RNA and proteins form large + small subunits

• can be attached to rough ER or dispersed in cytoplasm (aka free ribosomes)

rough ER (endoplasmic reticulum)

HAS ribosomes

synthesizes proteins

• integral membrane proteins

• proteins for secretion in extracellular space

  • later taken to golgi

smooth ER

same shape as rough ER but has NO ribosomes

manufactures lipids + carbohydrates

detox chemicals

stores calcium

golgi apparatus

modifies + packages + distributes proteins and lipids from ER for secretion or internal use
stacked, flattened membranous sacs (cisternae)

material from ER enters golgi during cis face and material is released during tran face

cis face

golgi apparatus

recieves transport vesicles from rough ER

tran face

golgi apparatus

pinches off vesicles and takes the vesicle to other locations

secretory vesicles

vesicles that pinch off of golgi

moves to surface of cell and fuse their membrane to the plasma membrane

• contents are released via exocytosis

• vesicle membrane fuses with plasma membrane

most times contents are not released to exterior until cell receives signal

lysosome

membrane-bound vesicle pinched off golgi

contains digestive enzymes

• breaks down food + viruses

• digest organelles of the cell that are no longer functional (autophagy)

peroxisome

membrane-bound vesicle

one site of lipid + amino acid degradation

• produces hydrogen peroxide

contains the enzyme catalase

• breaks down hydrogen peroxide into water + oxygen which cancels out the toxic hydrogen peroxide

cells that are active in detoxification have many

• liver, kidney

proteasome structure

tubelike protein in cytoplasm

break down proteins in cytoplasm

not surrounded by membranes

• inner surface has enzymatic regions that break down other proteins

• other proteins in the tube regulate what proteins are taken in for breakdown and recycle

mitochondria strucutre

has cristae - inner membrane projections

enclosed by a double membrane

• inner membrane has foldings called cristae

  • contains embedded proteins involved in cellular work

• outer membrane is permeable to small solutes

#powerhouseofthecell

major site of ATP synthesis when O2 is available

mitochondrial matrix

• contains enzymes for metabolic steps of cellular respiration

centriole structure

cylindrical + perpendicular to each other

located in the centrosome

center of microtubule formation

determine cell polarity during division

form basal bodies of cilia + flagella

cilia

extension of plasma membrane

contains parallel microtubules

moves materials over surface of cell

• requires ATP

flagellum

extension of the plasma membrane

contains parallel microtubules

longer than cilia

propels spermatozoa

moves the entire cell

typically only one

microvilli

extension of PM

contains microfilaments

increases SA of PM for absorption + secretion

modified to form sensory receptors