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Cell Structure and Function
Cells
• Smallest living unit
• Most are microscopic
Discovery of Cells
• Robert Hooke (mid-1600s)
– Observed sliver of cork
– Saw “row of empty boxes”
– Coined the term cell
Cell theory
• (1839)Theodor Schwann & Matthias Schleiden
“ all living things are made of cells”
• (50 yrs. later) Rudolf Virchow
“all cells come from cells”
Principles of Cell Theory
• All living things are made of cells
• Smallest living unit of structure and
function of all organisms is the cell
• All cells arise from preexisting cells
(this principle discarded the idea of
spontaneous generation)
Cell Size
Characteristics of All Cells
•
•
•
•
A surrounding membrane
Protoplasm – cell contents in thick fluid
Organelles – structures for cell function
Control center with DNA
Cell Types
• Prokaryotic
• Eukaryotic
Prokaryotic Cells
• First cell type on earth
• Cell type of Bacteria and Archaea
Prokaryotic Cells
• No membrane bound nucleus
• Nucleoid = region of DNA concentration
• Organelles not bound by membranes
Eukaryotic Cells
• Nucleus bound by membrane
• Include fungi, protists, plant,
and animal cells
• Possess many organelles
Protozoan
Representative Animal Cell
Representative Plant Cell
Organelles
• Cellular machinery
• Two general kinds
– Derived from membranes
– Bacteria-like organelles
Bacteria-Like Organelles
• Derived from symbiotic bacteria
• Ancient association
• Endosymbiotic theory
– Evolution of modern cells from
cells & symbiotic bacteria
Plasma Membrane
• Contains cell contents
• Double layer of phospholipids & proteins
Phospholipids
• Polar
– Hydrophylic head
– Hydrophobic tail
• Interacts with water
Movement Across the Plasma Membrane
• A few molecules move freely
– Water, Carbon dioxide, Ammonia, Oxygen
• Carrier proteins transport some molecules
– Proteins embedded in lipid bilayer
– Fluid mosaic model – describes fluid nature of
a lipid bilayer with proteins
Membrane Proteins
1. Channels or transporters
– Move molecules in one direction
2. Receptors
– Recognize certain chemicals
Membrane Proteins
3. Glycoproteins
– Identify cell type
4. Enzymes
– Catalyze production of substances
Cell Walls
• Found in plants, fungi, & many protists
• Surrounds plasma membrane
Cell Wall Differences
• Plants – mostly cellulose
• Fungi – contain chitin
Cytoplasm
• Viscous fluid containing organelles
• components of cytoplasm
–
–
–
–
Interconnected filaments & fibers
Fluid = cytosol
Organelles (not nucleus)
storage substances
Cytoskeleton
• Filaments & fibers
• Made of 3 fiber types
– Microfilaments
– Microtubules
– Intermediate filaments
• 3 functions:
– mechanical support
– anchor organelles
– help move
substances
A = actin, IF = intermediate filament, MT = microtubule
Cilia & Flagella
• Provide motility
• Cilia
– Short
– Used to move substances
outside human cells
• Flagella
– Whip-like extensions
– Found on sperm cells
• Basal bodies like
centrioles
Cilia & Flagella Structure
• Bundles of microtubules
• With plasma membrane
Centrioles
• Pairs of microtubular structures
• Play a role in cell division
Membranous Organelles
• Functional components within cytoplasm
• Bound by membranes
Nucleus
• Control center of cell
• Double membrane
• Contains
– Chromosomes
– Nucleolus
Nuclear Envelope
• Separates nucleus from rest of cell
• Double membrane
• Has pores
DNA
• Hereditary material
• Chromosomes
– DNA
– Protiens
– Form for cell division
• Chromatin
Nucleolus
• Most cells have 2 or more
• Directs synthesis of RNA
• Forms ribosomes
Endoplasmic Reticulum
• Helps move substances within cells
• Network of interconnected membranes
• Two types
– Rough endoplasmic reticulum
– Smooth endoplasmic reticulum
Rough Endoplasmic Reticulum
• Ribosomes attached to surface
– Manufacture protiens
– Not all ribosomes attached to rough ER
• May modify proteins from ribosomes
Smooth Endoplasmic Reticulum
• No attached ribosomes
• Has enzymes that help build molecules
– Carbohydrates
– Lipids
Golgi Apparatus
• Involved in synthesis of plant cell wall
• Packaging & shipping station of cell
Golgi Apparatus Function
1. Molecules come in vesicles
2. Vesicles fuse with Golgi membrane
3. Molecules may be modified by Golgi
Golgi Apparatus Function
(Continued)
4. Molecules pinched-off in separate vesicle
5. Vesicle leaves Golgi apparatus
6. Vesicles may combine with plasma
membrane to secrete contents
Lysosomes
• Contain digestive enzymes
• Functions
– Aid in cell renewal
– Break down old cell parts
– Digests invaders
Vacuoles
• Membrane bound storage sacs
• More common in plants than animals
• Contents
– Water
– Food
– wastes
Bacteria-Like Organelles
• Release & store energy
• Types
– Mitochondria
(release energy)
– Chloroplasts
(store energy)
Mitochondria
• Have their own DNA
• Bound by double membrane
Mitochondria
• Break down fuel molecules (cellular respiration)
– Glucose
– Fatty acids
• Release energy
– ATP
Chloroplasts
• Derived from photosynthetic bacteria
• Solar energy capturing organelle
Photosynthesis
• Takes place in the chloroplast
• Makes cellular food – glucose
Molecule Movement & Cells
• Passive Transport
• Active Transport
• Endocytosis
(phagocytosis & pinocytosis)
• Exocytosis
Passive Transport
• No energy required
• Move due to gradient
– differences in concentration, pressure, charge
• Move to equalize gradient
– High moves toward low
Types of Passive Transport
1. Diffusion
2. Osmosis
3. Facilitated diffusion
Diffusion
• Molecules move to equalize concentration
Osmosis
• Special form of diffusion
• Fluid flows from lower solute concentration
• Often involves movement of water
– Into cell
– Out of cell
Solution Differences & Cells
• solvent + solute = solution
• Hypotonic
– Solutes in cell more than outside
– Outside solvent will flow into cell
• Isotonic
– Solutes equal inside & out of cell
• Hypertonic
– Solutes greater outside cell
– Fluid will flow out of cell
Facilitated Diffusion
• Differentially permeable membrane
• Channels (are specific) help molecule
or ions enter or leave the cell
• Channels are usually made of transport
proteins
(aquaporins facilitate the movement of
water)
• No energy is used
Process of Facilitated Transport
• Protein binds with molecule
• Shape of protein changes
• Molecule moves across membrane
Active Transport
• Molecular movement
• Requires energy (against gradient)
• Example is sodium-potassium pump
Endocytosis
• Movement of large material
– Particles
– Organisms
– Large molecules
• Movement is into cells
• Types of endocytosis
– bulk-phase (nonspecific)
– receptor-mediated (specific)
Process of Endocytosis
• Plasma membrane surrounds material
• Edges of membrane meet
• Membranes fuse to form vesicle
Forms of Endocytosis
• Phagocytosis – cell eating
• Pinocytosis – cell drinking
Exocytosis
• Reverse of endocytosis
• Cell discharges material
Exocytosis
• Vesicle moves to cell surface
• Membrane of vesicle fuses
• Materials expelled
The Cell Cycle
&
Cell Division
The Cell Cycle
http://www.nobel.se/medicine/laureates/2001/press.html
MITOSIS
Mitosis
The process of cell division which results
in the production of two daughter cells
from a single parent cell.
The daughter cells are identical to
one another and to the original parent
cell.
Mitosis can be divided into stages
• Interphase
• Prophase
• Metaphase
• Anaphase
• Telophase & Cytokinesis
Interphase
The cell prepares for division
• Animal Cell
– DNA replicated
– Organelles replicated
– Cell increases in size
• Plant Cell
– DNA replicated
– Organelles replicated
– Cell increases in size
Interphase
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Prophase
The cell prepares for nuclear division
• Animal Cell
– Packages DNA into
chromosomes
• Plant cell
– Packages DNA into
chromosomes
Prophase
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Metaphase
The cell prepares chromosomes for
division
• Animal Cell
– Chromosomes line up
at the center of the cell
– Spindle fibers attach
from daughter cells to
chromosomes at the
centromere
• Plant Cell
– Chromosomes line up
at the center of the cell
– Spindle fibers attach
from daughter cells to
chromosomes at the
centromere
Metaphase
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Anaphase
The chromosomes divide
• Animal Cell
– Spindle fibers pull
chromosomes apart
– ½ of each
chromosome (called
chromotid) moves to
each daughter cell
• Plant Cell
– Spindle fibers pull
chromosomes apart
– ½ of each
chromosome (called
chromotid) moves to
each daughter cell
Anaphase
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Telophase
The cytoplasm divides
• Animal Cell
– DNA spreads out
– 2 nuclei form
– Cell membrane
pinches in to form
the 2 new daughter
cells
• Plant Cell
– DNA spreads out
– 2 nuclei form
– New cell wall forms
between to nuclei to
form the 2 new
daughter cells
Telophase
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Animal Mitosis -- Review
Interphase
Prophase
Metaphase
Anaphase
Telophase
Interphase
Plant Mitosis -- Review
Interphase
Prophase
Metaphase
Anaphase
Telophase
Interphase
MEIOSIS
Meiosis
Meiosis is the type of cell division by which
germ cells (eggs and sperm) are produced.
One parent cell produces four daughter
cells.
Daughter cells have half the number of
chromosomes found in the original
parent cell
Meiosis
During meiosis, DNA replicates
once, but the nucleus divides twice.
Meiosis
Four stages can be described for each
division of the nucleus.
Meiosis I
First division of meiosis
First Division of Meiosis
• Prophase 1: Each chromosome duplicates and
remains closely associated. These are called sister
chromatids.
• Metaphase 1: Chromosomes align at the center of the
cell.
• Anaphase 1: Chromosome pairs separate with sister
chromatids remaining together.
• Telophase 1: Two daughter cells are formed with
each daughter containing only one chromosome of the
chromosome pair.
Prophase I
http://everyschool.org/u/logan/cellreproductionx/rogersa/research/meiosis.html
Prophase I
http://everyschool.org/u/logan/cellreproductionx/rogersa/research/meiosis.html
Metaphase I
http://everyschool.org/u/logan/cellreproductionx/rogersa/research/meiosis.html
Telophase I
http://everyschool.org/u/logan/cellreproductionx/rogersa/research/meiosis.html
Meiosis
Second Division of Meiosis
Second Division of Meiosis
• Prophase 2: DNA does not replicate.
• Metaphase 2: Chromosomes line up at the center of
the cell
• Anaphase 2: Centromeres divide and sister
chromatids move separately to each pole.
• Telophase 2: Cell division is complete.
Four haploid daughter cells are formed.
Prophase II
http://everyschool.org/u/logan/cellreproductionx/rogersa/research/meiosis.html
Metaphase II
http://everyschool.org/u/logan/cellreproductionx/rogersa/research/meiosis.html
Telophase II
http://everyschool.org/u/logan/cellreproductionx/rogersa/research/meiosis.html
Meiosis
http://www.biosci.uga.edu/almanac/bio_103/notes/apr_3.html.
Differences in Mitosis & Meiosis
• Mitosis
–
–
–
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Asexual
Cell divides once
Two daughter cells
Genetic information is
identical
• Meiosis
– Sexual
– Cell divides twice
– Four haploid daughter
cells
– Genetic information is
different