Ch. 7 Cellular Structure and Function
I.
Cell discovery and Theory
Main Idea: the invention of the microscope led to the discovery
of cells.
A. History of the Cell Theory
1. the invention of the microscope led to the discovery of cells
a. Robert Hooke (1665): English
monk/scientist used a simple microscope to
view a piece of cork which reminded him of
monk’s “cells” or rooms in a monastery; he
was actually looking at dead cell walls.
b. Anton van Leeuwenhoek: Dutch scientist
who designed his own microscope and first
saw microorganisms.
B. Cell Theory: one of the fundamental principles of modern
Biology; 3 principles:
1) All living things are made of cells.
2) Cells are the basic unit of structure and function in
any organism.
3) All cells come from preexisting cells.
C. Basic Cell Types
1. ALL cells have:
a. plasma membrane that acts as a boundary
and helps control what enters and leaves the
cell
b. genetic material that provides instructions
for making substances that the cell needs.
c. Break down molecules for energy.
2. Cell categories:
a. Eukaryotic cells: contain membrane-bound
organelles (specialized structures that carry
out specific cell functions) and a nucleus
(central organelle that contains cell’s genetic
material in the form of DNA).
i. Most organisms are made of
eukaryotic cells and are called
“eukaryotes”; algae and yeast are
unicellular eukaryotes
b. Prokaryotic cells: cells without a nucleus or
other membrane-bound organelles.
i. “prokaryotes”: most unicellular
organisms like bacteria; probably
similar to the first life on Earth.
II.
The Plasma Membrane
Main Idea: The plasma membrane helps to maintain a cell’s
homeostasis.
A. Function of the Plasma Membrane: the plasma membrane
helps to maintain a cell’s homeostasis.
1. plasma membrane is a thin, flexible layer b/w the
cell and its environment that allows nutrients into
the cell and allows wastes and other products to
leave the cell.
2. selective permeability: property that allows some
substances to pass through the membrane while
keeping others out.
B. Structure of the Plasma Membrane
1. phospholipid bilayer: makes up the plasma
membrane where two layers of phospholipids are
arranged tail-to-tail.
a. Phospholipids look like a round head with
two tails
b. Phosphate is the polar head and is attracted
to water
c. The two fatty acid tails are nonpolar and are
repelled by water
d. The two layers create a barrier that is polar
on the surface and nonpolar in the middle
that prevents water-soluble substances from
easily moving through the membrane.
2. other components:
a. receptors: proteins on the membrane surface
that send signals to the inside of the cell
b. transport proteins: move needed substances
or waste materials through the plasma
membrane.
c. Cholesterol: positioned among the fatty acid
tails and prevents them from sticking
together
d. Carbohydrates: stick out from the
membrane and help identify chemical
signals and define a cell’s characteristics.
3. fluid mosaic model: concept of the plasma
membrane that describes how the phospholipids
and other components are in constant motion
within the membrane creating a pattern on the
surface.
III.
Structures and Organelles
Main Idea: Eukaryotic cells contain organelles that allow the
specialization and the separation of functions within the cell.
A. Cytoplasm and Cytoskeleton
1. cytoplasm: the semi-fluid material inside the
plasma membrane
a. in prokaryotes, all chemical processes take
place directly in the cytoplasm
b. in eukaryotes, chemical processes take place
within organelles in the cytoplasm
2. cytoskeleton: network of long, thin protein fibers
that form a framework for the cell and provide an
anchor for the organelles inside.
a. Microtubules: long, hollow protein
cylinders that form a rigid skeleton for the
cell and assist in moving substances.
b. Microfilaments: thin protein threads that
give the cell shape and enable the cell to
move.
B. Cell Structures (organelles): allow different chemical
processes to take place at the same time in different parts of the
cytoplasm.
1. nucleus: contains cell’s DNA which stores
information to make proteins for cell growth,
function and reproduction
a. nuclear envelope: double membrane that
surrounds the nucleus
b. chromatin: complex DNA attached to
protein spread throughout the nucleus
2. ribosomes: manufacture proteins
a. made of RNA and a protein
b. not bound by a membrane
c. made by nucleolus
d. some free-float in cytoplasm/ others are
bound the endoplasmic reticulum
3. endoplasmic reticulum (ER): membrane system of
folded sacs and channels that serves as the site for
protein and lipid synthesis
a. rough ER: areas where ribosomes are
attached for protein synthesis
b. smooth ER: areas where no ribosomes are
present; provides surface for synthesis of
carbohydrates and lipids
4. Golgi apparatus: flattened stack of membranes
that modifies, sorts and packages proteins into sacs
called vesicles. These vesicles fuse with the
plasma membrane to release proteins to the
environment outside the cell.
5. vacuoles: membrane-bound vesicles that can
temporarily store materials (food, enzymes) within
the cytoplasm.
a. animal cells usually do not contain vacuoles
6. Lysosomes: vesicles that contain substances that
digest excess or worn-out organelles and food
particles.
a. Protect cell by digesting bacteria and viruses
that enter the cell.
7. Centrioles: groups of microtubules that function
during cell division
a. Located in the cytoplasm in animal cells
near the nucleus.
8. Mitochondria: converts sugars into usable energy
a. Has highly folded inner membrane that
provides a surface for breaking bonds in
sugar molecules
b. “powerhouses” of the cell
9. chloroplasts: capture light energy and convert it to
chemical energy (photosynthesis)
a. present in plant and other eukaryotic cells
b. thykaloids: disk-shaped compartments
containing chlorophyll that trap solar
energy.
c. Plastid: group of organelles used for storage
(starch, lipids)
i. Chromoplasts: red (chromophyll),
orange or yellow (xanthophyll)
pigments that trap energy and give
color to flowers and leaves
10.cell wall: thick, rigid mesh of fibers that surrounds
the outside of the plasma membrane in plant cells,
protecting and supporting it.
a. Made of cellulose (carbohydrate)
11.cilia and flagella: microtubules that project
outside the plasma membrane that allow
movement.
a. Cilia are short, flagella are long and whiplike
C. Comparing cells
1. Plant cells: cell walls, chlorophyll with
chloroplasts, large vacuoles
2. Animal cells: no or small vacuoles present,
lysosomes
IV. Cellular Transport
Main Idea: Cellular transport moves substances within the cell and
moves substances into and out of the cell.
A. Diffusion: the movement of particles from an area of high
concentration of a substance to an area of lower concentration
of the substance.
1. occurs b/c particles in gases, liquids and solids are
in constant random motion (Brownian motion)
2. dynamic equilibrium: state reached where
particles continue to move but no change in
concentration occurs.
3. rate of diffusion is affected by concentration,
temperature and pressure
B. Diffusion across the plasma membrane: although water can
diffuse across the plasma membrane, the cell needs other
substances like chloride ions and sugars to perform cell
functions that can’t easily diffuse through the plasma
membrane.
1. facilitated diffusion: occurs when transport
proteins move ions and small molecules across the
plasma membrane. Requires no additional energy
(passive transport) since particles are moving from
area of high concentration to low concentration.
a. channel protein: transport protein that
allows substances to move into the cell by
opening and closing.
b. Carrier protein: transport protein that
changes shape to help move particles across
the plasma membrane
C. Osmosis: the diffusion of water across a selectively permeable.
1. water will move across to balance out the
concentration of a solute on both sides of a
selectively permeable membrane.
2. isotonic solution: occurs when a cell is in a
solution that has the same concentration of water
and solutes (ions, sugars, proteins) as in its
cytoplasm.
a. The cell is at equilibrium with the solution
and there is no net movement of water in or
out of the cell, so it retains its shape.
3. hypotonic solution: occurs when a cell is in a
solution that has a lower concentration of solute
than the cell’s cytoplasm.
a. Water moves into the cell and creates
osmotic pressure that causes animal cells to
swell or even burst if the pressure is too
great.
b. Cell walls prevent plant cells from bursting
in a hypotonic solution; the vacuole fills
with water pushing the cell membrane
against the cell wall causing the plant cell to
become firmer.
4. hypertonic solution: occurs when a cell is placed
in a solution with higher concentration of solute
than the cell’s cytoplasm.
a. water moves out of the cell and causes
animal cells to shrink
b. plant cells lose water from central vacuole
causing the cell membrane to shrink away
from the cell wall which causes the plant to
wilt.
D. Active Transport: the transport of substances from an area of
lower concentration to higher across the plasma membrane:
requires energy
1. carrier proteins called pumps can move only one
substance in only one direction, while others move
two substances either across the membrane in the
same direction or in opposite directions.
a. Na+/K+ATPase pump: found in plasma
membrane of animal cells
i. Maintains levels of sodium and
potassium ions inside and outside the
cell.
ii. Pump uses ATP (energy molecule) to
transport three sodium ions outside
the cell while moving two potassium
into the cell.
iii. Coupled transport: sodium atoms
pumped outside the cell couple with
sugar molecules and are transported
into the cell through a membrane
protein called a coupled channel
through facilitated diffusion.
E. Transport of Large Particles
1. endocytosis: cell surrounds an outside substance
with its plasma membrane, pinches off and leaves
the substance inside the cell in a vacuole.
2. exocytosis: reverse of endocytosis; cell expels
wastes and secrete substances (like hormones)
outside the cell
Both #1 and #2 require energy.