Chapter 3: Cells
Introduction Cell: Basic unit of life Adult human contains ~75 trillion cells Cells are very diverse in size, shape,
function› Ex: Neuron – long thin axons coupled with
cell body – serve to move electric signals throughout body
› Ex: Red Blood Cell – doughnut-shaped, small, carry oxygen to organs
Basic cell types Two types:
› 1) Prokaryotic› 2) Eukakryotic
Prokaryotic cell:› Do NOT contain nucleus› DNA found in cytoplasm› Do NOT contain membrane-bound
organelles› Simpler› Smaller (usually unicellular)
Basic cell types Eukaryotic cell:
› DOES contain nucleus› DNA found in nucleus› DOES contain membrane-bound organelles
Ex: mitochondria, ER, golgi, lysosomes, vacuole
› More complex› Larger size (usually a part of a multicellular
organism)
Basic cell components
ALL cell contain:› Cell/plasma membrane
a membrane which encloses to cell Serves to protect cell from pathogens and
permit molecules to pass into cell› Cytoplasm
Houses the cells organelles and genetic material
› Ribosomes Protein synthesis takes place here
› DNA/RNA Genetic material
Cell membrane Also called plasma membrane Boundary that separates cell’s
contents from the external environment
Actively functioning component of cell› Regulates the movement of substances in
and out of the cell› Helps cells to adhere to other cells
(important in forming tissues)
Cell membrane Characteristics:
› 1) Thin, flexible› 2) Outpockets and infoldings (increase
surface area)› 3) Selectively permeable (only allows some
molecules in/out)
Cell membrane Structure:
› 1) Lipid bilayer Two layers of phospholipids
Tails face inward (fat-like; hydrophobic – water hating)
Heads face out (phosphate; hydrophilic – water loving)
› 2) Cholesterol Keeps membrane fluid in cold weather
› 3) Proteins Structure and cell communication
› 4) Carbohydrates Cell communication
Cell membrane Membrane proteins:
› Transmembrane/integral: Help to transport ions and other molecules Structure
› Peripheral/Extensions: Connection of organelles to membrane Structure Cell communication
› CAM Cellular adhesion molecule Guides a cell’s interactions with other cells Ex: CAMs help white blood cells move to injury
Cytoplasm Contains organelles Contains cytoskeleton
› Network of protein fibers that form a support system
Usually slightly neutral pH Serves to help cells communicate
signals
Eukaryotic cell organelles
Endoplasmic Reticulum
Called ER Two types:
› Smooth: No ribosomes found on
surface (appears smooth) Contains enzymes
important in lipid synthesis, absorption of fat, metabolism of drugs
› Rough Contains ribosomes Site of protein synthesis –
sends items to smooth ER and Golgi for further processing
Ribosomes
Site of protein synthesis Two types:
› 1) Attached (to rough ER)› 2) Free (found floating in cytoplasm)
Parts:› Protein› RNA molecule (rRNA – ribosomal RNA)
Golgi apparatus Stacks of membrane-
bound sacs Takes in proteins
› Then, refines, packages and delivers final proteins
› Arrive to Golgi enclosed in vesicles
› Vesicles fuse with Golgi› As move through Golgi,
the proteins are modified chemically
› When reach outermost layer, packaged again in vesicles and shipped
Mitochondria
Major sites of cellular respiration (breakdown food to form energy - ATP)
Can reproduce Contain own DNA Contains outer and inner membrane
› Inner membrane folds inward to form cristae (fingers)
Matrix: inner space Many mitochondria found in muscle cells
(which require a LARGE amount of energy)
Lysosomes & Peroxisomes
Lysosomes:› Tiny sacs containing
enzymes that break down nutrient molecules, foreign particles, broken organelles
Peroxisomes:› Tiny sacs containing
enzymes that catalyze the synthesis of bile acids, detox hydrogen peroxide, breakdown lipids, detox alcohol
› Abundant in liver and kidney
Cilia and Flagella Cilia:
› Tiny hairs› Assist in movement› Move fluids (like mucus)
over tissues Flagella:
› Tail-like extensions› Assist in movement› Usually cells contain
single flagella› Ex: sperm
Vacuoles (vesicles) Membrane-bound sacs formed by cell
membrane folding inward Used for storage of macromolecules,
water, toxins, pigments
Microtubules/filaments
Microfilaments:› Actin proteins› Provide cell
movement (contraction, cilia/flagella)
Microtubules:› Tubulin protein› Thicker
Thin, thread-like strands within cytoplasm
Integral part of cytoskeleton
Nucleus Functions:
› House genetic material› Direct all cell activities
Enclosed by nuclear membrane (lipid bilayer)› Contain pores which allow molecules to exit
Found within nucleus:› Nucleolus: small, dense organelle made of
RNA and protein, forms ribosomes› Chromatin: loosely coiled fibers of DNA and
proteins (chromosomes)
Movement through cell membrane
Introduction to cell movement
Cell membrane is semi-permeable Rely upon concentration gradients to move
› Def: difference in concentration between two areas› Continually work to reach a state of equilibrium
(uniform concentration) Two types of cellular movement:
› 1) Passive transport: No energy required Ex: diffusion, osmosis, facilitated diffusion, filtration
› 2) Active transport Energy required Ex: exocytosis, endocytosis, proton pumps
Passive transport mechanisms
Diffusion Passive transport (no energy use) Molecules/Ions spread from regions where
they are more concentrated to less concentrated
Can occur if:› Membrane allows it› Concentration gradient exists
Ex: oxygen and carbon dioxide moving in/out of blood
Animation
Facilitated diffusion Passive transport (no energy use) Molecules/Ions spread from regions where
they are more concentrated to less concentrated
Can occur if:› Membrane allows it› Concentration gradient exists› Membrane proteins assist(change shape when
molecule attaches) Ex: movement of glucose and amino acids Animation
Osmosis Passive transport (no energy use) WATER molecules spread from regions
where they are more concentrated to less concentrated
Can occur if:› Membrane allows water (but usually not other
molecules) to pass through› Concentration gradient exists
Osmosis Solution can be:
› Hypertonic: Higher osmotic pressure inside More water –less solutes - on
inside of the cell Result: water rushes OUT, cell
shrinks› Hypotonic:
Lower osmotic pressure inside Less water – more solutes – on
inside of the cell Result: water goes IN, cell
expands
Osmosis
Solution can be:› Isotonic:
Same osmotic pressure on body sides Molecules CONTINUE TO MOVE Net concentration of water and solutes does not
change!
Animation
Filtration Passive transport (no energy use) Molecules are FORCED from regions where
they are more concentrated to less concentrated
Usually used to separate solids from water Relies upon hydrostatic pressure
(created by weight of water due to gravity) to force molecules
Teacher Demo (applesauce and water)
Active transport mechanisms
Active transport Requires use of energy (ATP molecules) Also requires the use of special membrane-
bound proteins to assist molecule movement› Carrier proteins (change shape when molecule
attaches) Moves particles AGAINST concentration
gradient (low to high) May use up to 40% of cell’s energy Ex: Proton pump, Na/K pump, movement of
nutrients into cells that line intestines
Endocytosis Requires use of energy (ATP molecules) Molecules too large to enter cell through
passive transport Molecules are packaged inside vesicles (using
infolding of cell membrane) Molecule moves INWARD
Endocytosis
Three forms:› Phagocytosis:
Cell “eating” Take in solid particles (bacteria, debris)
› Pinocytosis: Cell “drinking” Take in liquid particles (water w/ dissolved items)
› Receptor-mediated: Moves specific kinds of particles into cell Proteins extend to outer surface where they form
receptors Bind to ligands
Exocytosis Requires use of energy (ATP molecules) Molecules too large to leave cell through
passive transport Molecules are packaged inside vesicles and
SECRETED OUT Molecule moves OUTWARD
Cell Cycle
Cell cycle Series of changes cell undergoes from its
formation to its division Rate of cell cycle depends upon checkpoints
and stimulation› Ex: restriction checkpoint
Determines cell’s fate (division, resting, death)› Cancer: inability of cell to respond to checkpoints,
cells divide uncontrollably› Stimulation: cells will divide spontaneously when
hormone or growth factor triggers it Ex: development of milk during pregnancy
Cell cycle Includes:
› Interphase: preparatory phase Grows, makes copies of organelles,
obtains nutrients replicates DNA Three stages: G1, S, G2
Cell cycle Includes:
› Mitosis: Nuclear division Phases: Prophase, Metaphase,
Anaphase, Telophase Prophase: chromosomes condense (become visible),
centrioles migrate to opposite ends, nuclear envelope disappears
Metaphase: chromosomes line-up in middle, spindle fibers attach to centromeres
Anaphase: chromosomes separate, cell elongates Telophase: final stage, chromosomes unwind (go
back to chromatin), nuclear envelope reforms (prophase in reverse!)
Cell cycle Includes:
› Cytokinesis: Cytoplasmic division Animals:
Cell membrane begins to constrict, pinch inward
Creates cleavage furrow
Uses microfilaments to contract and pinch
› Animation
Cell differentiation Differentiation:
› Def: Process of cell specialization
› Cell gains function/structure Stem cells:
› Def: cells who have NOT gained specialization, divide frequently
› Divides through mitosis continually (two options) 1) Forms 2 daughter cells 2) One daughter cell and one
progenitor cell Progenitor cell: partially
specialized cell
Cell death Apoptosis:
› Cell that does not divide or specialize
› Cell death› Normal part of development
Ex: fetus – rids hands of webbing
› Could also be due to injury or disease Ex: sunburn (peeling skin)