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)