Transcript Chapter 1 The cell membrane & the cell wall

Chapter 1
Topic 3
The cell membrane & the cell wall
Chapter outline
–
The cell membrane
•
The cell membrane regulates the flow of materials into
and out of a cell.
•
It is selectively permeable, meaning that only certain
materials can pass through the membrane.
•
A cell membrane consists of a bilayer of phospholipids
with protein molecules jutting through one or both
layers.
The cell wall
– Prokaryotic cell wall
• The prokaryotic cell wall consists of long polymers called
peptidoglycans.
• Some prokaryotic cell walls have a second, outer layer composed of
lipoproteins and lipopolysaccharides.
– Eukaryotic cell wall
• The eukaryotic cell wall has three parts: the primary cell wall, the
middle lamella, and the secondary cell wall.
• The primary cell wall, composed mainly of cellulose, is the innermost
layer of the wall.
• The middle lamella contains polysaccharides called pectins.
• The secondary cell wall is the outermost layer. It consists of cellulose
and a strengthening material called lignin.
Terms to know
•
•
•
•
•
•
•
•
•
•
•
•
active transport - Transport in which a cell must expend energy. Active transport occurs
against a concentration gradient.
basal body - A structure found at the connection of cilia and flagella with the cell membrane.
It is composed of microtubules in a circular configuration of nine triplets.
cell membrane - The structure which surrounds the cell and regulates the movement of
materials into and out of the cell. It is composed mostly of phospholipids.
cell wall - A structure found in most prokaryotes and some eukaryotes which gives the cell
greater structure. In prokaryotes, it is composed of peptidoglycans, and in eukaryotes, it
consists or polysaccharides, pectins, and lignin.
cilia - Tiny hairs along the outside of the cell membrane which are used to move the cell and
capture food particles.
chloroplast - The organelle in which photosynthesis takes place. It contains chlorophyll.
chromoplast - An organelle in which photosynthesis take place. It contains pigments other
than chlorophyll, resulting in a color other than green.
contractile vacuole - An organelle which pumps excess water of a cell to prevent it from
bursting.
endoplasmic reticulum - A network of tunnels which extend away from the nucleus, used
for the transport of proteins.
facilitated diffusion - A method of transport across the cell membrane by which carrier
proteins bond to a molecule on one side of the membrane, move through the membrane, and
then release it on the other side.
flagella - Large hairs which can whip back and forth to propel a cell.
Golgi body - Stacks of membranous pouches which act as a transport station, packaging
proteins from the endoplasmic reticulum and placing them into tiny vesicles.
Terms to know continued….
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
intermediate filament - A part of the cytoskeleton with a strong, ropelike structure which gives
the cell strength and helps it to maintain its shape.
leucoplast - Colorless plastids in autotrophs which store starch, proteins, and lipids.
lysosome - A sac similar to a vacuole which contains powerful digestive enzymes used to break
down large food particles.
microfilament - A part of the cytoskeleton which consists of actin and aids in cell movement.
microtrabeculae - Tiny fibers which interconnect all of the structures within the cell and help to
give the cell shape.
microtubule - Fibers which extend from the center of the cell to the cell membrane. They are
involved in cell reproduction and are part of the composition of cilia and flagella.
mitochondria - The organelle in which cellular respiration occurs.
nucleolus - A structure within the nucleus at which ribosomes are created.
nucleus - The organelle in eukaryotes which contains the cells DNA and thus indirectly controls
protein production and the rest of the cell.
passive transport - A form of transport which allows highly polar molecules to move through
the cell membrane without the expenditure of energy. This may occur either through protein
channels or facilitated diffusion.
peroxisome - An organelle similar to a vacuole which contains oxidizing enzymes which can
help neutralize toxic substances.
pseudopod - Extensions of the cytoplasm toward which the rest of the cytoplasm tends to flow.
Pseudopodia can be used for movement and the capture of prey.
ribosome - Structures found mainly in the endoplasmic reticulum whose function is to
synthesize protein based upon the code of a messenger RNA molecule.
vacuole - Membrane-bound sacs within a cell used to hold food particles, water, etc.
vesicle - A tiny vacuole, often used to carry protein molecules packaged at the Golgi bodies.
Plasma Membrane
• The plasma membrane is a selective barrier that
allows sufficient passage of oxygen, nutrients, and
waste to service the volume of every cell
• The general structure of a biological membrane is
a double layer of phospholipids
Animation: Membrane Selectivity
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
The fluid-mosaic
model of the cell
membrane
Outside of cell
(a) TEM of a plasma
membrane
Fig. 6-7 The plasma membrane
Inside of
cell
0.1 µm
Carbohydrate side chain
Hydrophilic
region
Hydrophobic
region
Hydrophilic
region
Phospholipid
Proteins
(b) Structure of the plasma membrane
Extracellular components and connections between cells
help coordinate cellular activities
• Most cells synthesize and secrete materials
that are external to the plasma membrane
• These extracellular structures include:
– Cell walls of plants
– The extracellular matrix (ECM) of animal cells
– Intercellular junctions
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Cell Walls of Plants
• The cell wall is an extracellular structure that distinguishes plant cells
from animal cells
• Prokaryotes, fungi, and some protists also have cell walls
• The cell wall protects the plant cell, maintains its shape, and prevents
excessive uptake of water
• Plant cell walls are made of cellulose fibers embedded in other
polysaccharides and protein
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• Plant cell walls may have multiple layers:
– Primary cell wall: relatively thin and flexible
– Middle lamella: thin layer between primary
walls of adjacent cells
– Secondary cell wall (in some cells): added
between the plasma membrane and the primary
cell wall
• Plasmodesmata are channels between
adjacent plant cells
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Middle
lamella
1 µm
Central vacuole
Cytosol
Plasma membrane
Plant cell walls
Plasmodesmata
Fig. 6-28 Plant cell walls
Secondary
cell wall
Primary
cell wall
STOP !!! Don’t overworked
The Extracellular Matrix (ECM) of Animal Cells
• Animal cells lack cell walls but are covered by
an elaborate extracellular matrix (ECM)
• The ECM is made up of glycoproteins such as
collagen, proteoglycans, and fibronectin
• ECM proteins bind to receptor proteins in the
plasma membrane called integrins
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-30 Extracellular
matrix (ECM) of an
animal cell
Collagen
Proteoglycan
complex
EXTRACELLULAR FLUID
Polysaccharide
molecule
Carbohydrates
Fibronectin
Core
protein
Integrins
Proteoglycan
molecule
Plasma
membrane
Proteoglycan complex
Microfilaments
CYTOPLASM
ASSIGNMENTS.
Due on 29th June 2011 before 5 pm.
One of the functions of the cytoskeleton
in animal cells is to give shape to the cell.
Plant cells have a fairly rigid cell wall
surrounding the plasma membrane. Does
this mean that a cytoskeleton is
unnecessary for a plant cell? Defend your
answer in terms of other functions of the
cytoskeleton.
Functions of the ECM:
Support
Adhesion
Movement
Regulation
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Intercellular Junctions
• Neighboring cells in tissues, organs, or organ
systems often adhere, interact, and communicate
through direct physical contact
• Intercellular junctions facilitate this contact
• There are several types of intercellular junctions
–
–
–
–
Plasmodesmata
Tight junctions
Desmosomes
Gap junctions
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Plasmodesmata in Plant Cells
• Plasmodesmata are channels that
perforate plant cell walls
• Through plasmodesmata, water and small
solutes (and sometimes proteins and RNA)
can pass from cell to cell
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-31 Plasmodesmata between
plant cells
Cell walls
Interior
of cell
Interior
of cell
0.5 µm
Plasmodesmata Plasma membranes
Tight Junctions, Desmosomes, and Gap Junctions in
Animal Cells
• At tight junctions, membranes of neighboring
cells are pressed together, preventing leakage of
extracellular fluid
• Desmosomes (anchoring junctions) fasten
cells together into strong sheets
• Gap junctions (communicating junctions)
provide cytoplasmic channels between adjacent
cells
Animation: Tight Junctions
Animation: Desmosomes
Animation: Gap Junctions
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-32 Intercellular junctions in animal tissues
Tight junction
Tight junctions prevent
fluid from moving
across a layer of cells
0.5 µm
Tight junction
Intermediate
filaments
Desmosome
Gap
junctions
Space
between
cells
Plasma membranes
of adjacent cells
Desmosome
1 µm
Extracellular
matrix
Gap junction
0.1 µm
See U Next Class !!!