Transcript Unit 3 - Cell Structure and Function

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”
Cell Structure Reflects
Function

Cellular structures have evolved because of a
need for a particular function, for example:
 Neurons have axons to transfer information
to other cells
 Sperm have whiplike tails to enable them
to swim
 Eggs have large quantities of nutrients to
aid early embryonic development
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)
Cells are Small!
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
 Evolution
theory
of modern cells from
cells & symbiotic bacteria
Distinguishing Features of the Two Major Cell Types
Prokaryotes
Eukaryotes
No nucleus; nucleoid
Nucleus surrounds genome/DNA
Very small (~1-10 m)
Larger (~10-1000 m)
Few internal membranes
Many internal membranes
No cytoskeleton
Extensive cytoskeleton intracellular filaments
Corkscrew flagellum made
of a single protein
Complex flagella made of >300 proteins!
Peptidoglycan cell wall
Cellulosic cell walls if present
Small ribosomes (70S)
Big ribosomes (80S)
Homeostasis
 All
organisms must maintain a balance
regardless of internal and external
conditions
 This task is controlled by the plasma
membrane
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
Plasma Membrane
 The
plasma membrane serves as the
boundary between the cell and its
environment
 Allows
specific amount of nutrients to enter
and allow waste to exit
Characteristics of cell
membrane
permeable – allows some
molecules to enter and keeps others out
 Selectively
 Like
a screen door
Plasma Membrane
 Made
up of two
layers of
phospholipids
 Controls what
moves into and out
of the cell
 Selectively
permeable
 AKA: Lipid Bilayer,
Fluid Mosaic, Cell
Membrane
Capsule
 Found
on some
prokaryotic bacterial cells.
 Layer that lies outside the cell wall
 Usually composed of polysaccharides
 It enhances the ability of bacteria to
cause disease (ie. E. coli)
 Slippery
 Contains
water (protection from
desiccation)
 Helps cells stick to surfaces (other cells)
Cell Wall
 Rigid
structure
 Located outside of
plasma membrane
 Found in plant cells,
fungi, some bacteria
and protists
 Provides support and
protection
 Composed of
cellulose
(carbohydrate)
Nucleus
 Control
center of
the eukaryotic cell
 Contains
directions to
make proteins
 Chromatin –
strands of genetic
material (DNA)
Nucleolus

Structure within the
nucleus
 Produces ribosomes
Ribosomes
 The
site of protein
synthesis
 Found in the
cytoplasm or on
the Endoplasmic
Reticulum
Cytoplasm

Clear, gelatinous
fluid inside the cell
 Helps suspend
organelles
Endoplasmic Reticulum

Site of cellular
chemical reactions
 Series of highly
folded membranes
 Rough Endoplasmic
Reticulum – have
ribosomes attached
 Smooth Endoplasmic
Reticulum – does not
have ribosomes
attached
Golgi Apparatus

AKA: Golgi Body
 Flattened system of
tubular membranes
 Modifies and
packages proteins
 Sort proteins to be
sent to appropriate
destination
Vacuoles

Temporary storage of
materials
 Store food, enzymes,
other materials
needed by the cell,
and waste
 Plant cells usually
have one large
vacuole, animal cells
usually contain many
smaller vacuoles
Lysosomes
 Contain
digestive
enzymes that
digest excess or
worn out
organelles, food
particles, viruses
and bacteria
Chloroplasts

Found in the cells of
green plants
 Organelle that
captures light
energy and
produces food to
store for later use
 Contains chlorophyll
– gives plants their
green color
Mitochondria

Organelles that
transform energy for
the cell
 Double membrane
structure with highly
folded inner
membrane
Cytoskeleton

Support structure for
the cell
 Composed of
microtubules and
microfilaments
 Helps cell to
maintain shape
Cilia and Flagella

Aid in locomotion or
feeding
 May move the entire
cell, or aid in
movement of
substances across
the cell surface
Cilia and Flagella
video
Pseudopodia
 Means
fake or false feet
 Temporary projections of eukaryotic cells.
 This is how amoebas move, as well as
some cells found in animals, such as white
blood cells
 Pseudopodia extend and contract by the
reversible assembly of actin subunits into
microfilaments. Filaments near the cell's
end interact with myosin which causes
contraction.
 Amoeboid movement
More on the Cytoskeleton
 Mitosis
 Specific
cellular forms
 Muscle
 Nerve
cells
 Video
link
Plant and Animal Cells

Animal Cells
- Don’t have a cell
wall
- Contain centrioles
- Contain many
small vacuoles

Plant Cells
- Generally larger
than animal cells
- Have a cell wall
- Contain
chloroplasts
- Have one large
central vacuole
Critical Thinking : Why are plant and animal cells
similar?
Identify the Following Cellular
Structures
Advantages of highly folded Membranes
 Folded
membranes are an
advantage to a cell because
 Cell
processes can be more efficient
 Membranes provide a larger surface
area for cell process to take place
 Remember
all cell membranes are
made up of phospholipids
 Examples:
 folded
membranes in organelles like
mitochondria
 Microvilli
Endomembrane
System
 The
endomembrane
system is composed
of a number of inter-related membrane
sacs within the cytoplasm of the cell
 Rough
and smooth ER, Golgi apparatus,
Vessicles, Lysosomes
 The
endomembrane system functions in
protein synthesis, protein modification,
sorting and transport
 Animation
Inner Life of the Cell
 Long
Version
 Short Version