Cell Theory
Virchow, Schleiden and Schwann
1. Every organism is composed of one or
more cells
2. Cells are the smallest units having
properties of life
3. Continuity of life arises from growth and
division of single cells
- Cells arise only from pre-existing cells.
How many cells in your body?
50 million million (trillion)
That’s 50,000,000,000,000 cells!!!!!!
And not only that, there are many different
types.
Cells are diverse

But only two basic types
Two Basic Cell Types
Prokaryote
Eukaryote
Pro = before
karyote = nucleus
Eu = true
karyote = nucleus
very small
large
True
Nucleus
present
No
yes
Organelles
Present
No
Yes
Name
Relative
size
DNA
structure
Examples
loose, sometimes
circular
Bacteria
packed into
chromosomes
Plants, animals, protists
Prokaryotic Cell
Note the lack of nucleus, DNA free
floating (nucleoid area)
DO HAVE plasma membrane, ribosomes,
and cell wall (sometimes)
Endosymbiotic
Theory
It is believed that eukaryotic cells
arose from groups of prokaryotic
cells living together.
Smaller ones inside larger ones.
EVIDENCE… For Endosymbiosis





Some eukaryotic organelles resemble
bacteria
Mitochondria and Chloroplast – double
membrane
Mitochondria and bacteria have similar
size
Mitochondria and Chloroplast DNA
circular like Bacteria
Mitochondria divide as bacteria do
Eukaryotic Cell
More Advanced, larger & have organelles
DO HAVE nucleus, ribosomes,
mitochondria, chloroplasts (plants), cell
wall (plants), endoplasmic reticulum, golgi
complex, lysosomes, and vacuoles
Eukaryotic Cell
Lots of internal
membranebound
structures!
Why are cells so small?
Cells exchange all materials with their
environment through the cell membrane.
Exchange is faster in a smaller cell.
Need a surface area proportional to their
volume – Surface area to volume ratio
decreases as cell gets larger.
Cells that are specialized for absorption
have folds in plasma membrane to
increase surface area
Plasma Membrane
Plasma Membrane
Both prokaryotic and eukaryotic cells have
this “outer wall”
Holds the CYTOPLASM inside the cell
Gives cells their shape and flexibility
Helps to maintain HOMEOSTASIS by
allowing substance to flow in and out of
the cell – SELECTIVE PERMIABILITY
Structure of Plasma Membrane
The plasma membrane is a PHOSPHOLIPIID
BILAYER
PHOSPHOLIPID
BILAYER
Structure of Plasma Membrane
Fluid Mosaic Model

Phospholipids, cholesterol, and proteins all
flow like the surface of a wavy lake, moving
and shifting.
What are the structures and
functions of the cell membrane?
Components of the Cell Membrane
Contains lipids, carbohydrates, and functional proteins
Phospholipid Bilayer
Double layer of phospholipid molecules:


hydrophilic heads—toward watery environment,
both sides
hydrophobic fatty-acid tails—inside membrane
Membrane Proteins
Integral proteins:

within the membrane
Peripheral proteins:

inner or outer surface of the membrane
Cytoplasm
All materials inside the cell and
outside the nucleus:
cytosol (fluid):
dissolved materials:
 nutrients, ions, proteins, and waste
products
 organelles:
structures with specific functions

What are cell organelles & their
functions?
Nonmembranous organelles:


no membrane
direct contact with cytosol
Membranous organelles:


covered with plasma membrane
isolated from cytosol
6 types of nonmembranous organelles:



cytoskeleton
microvilli
centrioles



cilia
ribosomes
proteasomes
The Cytoskeleton
Structural proteins for shape
and strength
Microfilaments

Thin filaments composed of the
protein actin:
provide additional mechanical strength
interact with proteins for consistency
Pairs with thick filaments of myosin
for muscle movement
Intermediate

Mid-sized between microfilaments
and thick filaments:
durable (collagen)
strengthen cell and maintain shape
stabilize organelles
stabilize cell position
The Cytoskeleton
Microtubules

Large, hollow tubes of
tubulin protein:
attach to centrosome
strengthen cell and anchor
organelles
change cell shape
move vesicles within cell
(kinesin and dynein)
form spindle apparatus
Microvilli
Increase surface area for absorption
Attach to cytoskeleton
Centrioles in the Centrosome
Centrioles form spindle
apparatus during cell
division
Centrosome: cytoplasm
surrounding centriole
Cilia Power
Hair-like cilia move fluids
across the cell surface
Ribosomes
Build polypeptides in protein
synthesis
Two types:

free ribosomes in cytoplasm:
proteins for cell

fixed ribosomes attached to
ER:
proteins for secretion outside cell
Proteasomes
Contain enzymes (proteases)
Disassemble damaged proteins for recycling
Membranous Organelles
5 types of membranous organelles:
 endoplasmic reticulum (ER)
 Golgi apparatus
 lysosomes
 peroxisomes
 mitochondria
Endoplasmic Reticulum (ER)
endo = within
plasm = cytoplasm
reticulum = network
Cisternae are storage chambers within
membranes
Functions of ER
Synthesis of proteins, carbohydrates,
and lipids
Storage of synthesized molecules and
materials
Transport of materials within the ER
Detoxification of drugs or toxins
Smooth Endoplasmic Reticulum (SER)
No ribosomes attached
Synthesizes lipids and carbohydrates:




phospholipids and cholesterol (membranes)
steroid hormones (reproductive system)
glycerides (storage in liver and fat cells)
glycogen (storage in muscles)
Rough Endoplasmic Reticulum (RER)
Surface covered with ribosomes:



active in protein and glycoprotein synthesis
folds polypeptides protein structures
encloses products in transport vesicles
Golgi Apparatus
Vesicles enter forming face and exit maturing face
 Secretory vesicles:
modify and package products
for exocytosis

Membrane renewal
vesicles:
add or remove membrane
components

Transport vesicles:
Carry materials to and
from Golgi apparatus
Cis face, closer to ER
Trans face, closer to cell
Lysosomes
Powerful enzymecontaining vesicles:

lyso = dissolve,
soma = body
Exocytosis

Primary lysosome:
 formed by Golgi
and inactive
enzymes
Secondary
lysosome:
 lysosome fused
with damaged
organelle
 digestive
enzymes
activated
 toxic chemicals
isolated
Ejects secretory products and wastes
Lysosome Functions
Clean up inside cells:
 break down large molecules
 attack bacteria
 recycle damaged organelles
 ejects wastes by exocytosis
Autolysis
Self-destruction of damaged cells:





auto = self, lysis = break
lysosome membranes break down
digestive enzymes released
cell decomposes
cellular materials recycle
Peroxisomes
Are enzyme-containing vesicles:



break down fatty acids, organic compounds
produce hydrogen peroxide (H2O2) …TOXIC
replicate by division
KEY CONCEPT
Cells: basic structural and
functional units of life
 respond to their environment
 maintain homeostasis at the
cellular level
 modify structure and function
over time
Mitochondrion
Structure
2 Membranes
Have smooth outer membrane and folded inner
membrane (cristae)
Matrix:

fluid around cristae
Mitochondrial Function
Mitochondrion takes chemical energy from
food (glucose):

produces energy molecule ATP
Nucleus
Nucleus
Control Center of the cell
Contain CHROMATIN (loose DNA)

Bundles into CHROMOSOMES when cell is
ready to divide (it packs before moving)
Chromatin
Chromosomes
Chromatin in the Nucleus
Directs PROTEIN SYNTHESIS (building
proteins)
It contains the “blueprints”


“Blueprints” are Called DNA
DNA in loose coils called chromatin
How does the nucleus control the
cell?
Nucleus:

largest organelle
Nuclear envelope:

double membrane
around the nucleus
Perinuclear space:

between 2 layers of
nuclear envelope
Nuclear pores:

communication
passages
Nucleus Controls Cell
Structure and Function
Direct control through synthesis of:


structural proteins
secretions (environmental response)
Indirect control over metabolism through
enzymes
Within the Nucleus
DNA:

all information to build and run organisms
Nucleoplasm:

fluid containing ions, enzymes, nucleotides,
and some RNA
Nuclear matrix:

support filaments
Nucleoli in Nucleus
Are related to protein production
Are made of RNA, enzymes, and histones
Synthesize rRNA and ribosomal subunits
Organization of DNA
Nucleosomes:

DNA coiled around
histones
Chromatin:

loosely coiled DNA
(cells not dividing)
Chromosomes:

tightly coiled DNA
(cells dividing)
Figure 3–11
What is genetic code?
DNA and Genes
DNA:

instructions for every protein in the body
Gene:

DNA instructions for 1 protein
Genetic Code
The chemical language of DNA instructions:


sequence of bases (A, T, C, G)
triplet code:
3 bases = 1 amino acid
KEY CONCEPT
The nucleus contains
chromosomes
Chromosomes contain DNA
DNA stores genetic instructions for
proteins
Proteins determine cell structure
and function
Cell Walls
Outside of the plasma membrane
Can be made of thick fibers of cellulose
(plants), chitin (fungi), or peptodoglycan
(some bacteria)
Plant cells have openings in cell wall
called GAP JUNCTIONS for cell to cell
communication
Animal cells DO NOT have cell walls
Cell Wall of Plants
Is this a prokaryotic or eukaryotic cell?