Chapter 7: Cell Structure and Function
(7:1) Cell: The basic unit of life
I.
(7:2)
II.
Cell Theory
a. All living things are composed of cells
b. Cells are the basic units of structure and function in living things
c. All cells come from pre-existing cells.
Cell Structure and organelles
a. Structure within cells
i. Cells of animals, plants, and related organisms have 2 basic parts
1. The nucleus – the control center
2. The cytoplasm – the material between cell membrane and
nucleus.
a. There are also organelles: “little organs” with
specific jobs inside of the cell
b. Nucleus:
i. Not all cells have nuclei; unicellular bacteria
1. Eukaryotic cells: cells that have a nucleus (eukaryotes)
2. Prokaryotic cells: cells that don’t have a nucleus
(prokaryotes)
ii. Function:
1. The information center of the cell:
a. Contains DNA – instructions for making thousands
of different molecules and other cells
b. Directs all cell activity (remember Nucleic Acids)
2. Nuclear Envelope:
a. Two membranes that surround the nucleus
i. Contain nuclear pores (small openings) for
molecules to move in and out of the nucleus.
3. Nucleolus:
a. Made up of RNA (single stranded DNA) and
proteins
i. Where ribosomes are made
1. Aid in the production of proteins in
the cell
4. Chromosomes:
a. The condensed form of Chromatin: consists of
DNA bound to protein (most of the time spread
throughout the nucleus – spaghetti like)
i. Contains genetic information that gets
passed on from generation to generation.
c. Cytoplasm:
i. Area between the nucleus and the cell membrane
ii. Contains many important structures – organelles (which can move
around inside the cell because of the cytoplasm)
1. Cytoskeleton: composed of filaments and fibers that
support cell structure and drive cell movement.
a. Composed of microtubules: hollow tubes made of
protein
i. Provide support and shape
ii. Aid in cell division and movement of
organelles
iii. Support cilia (short threadlike) and flagella
(longer, whiplike) in some cells
1. helps unicellular cells move
2. aid in movement of substances along
surface
b. Composed of microfilaments: made up of proteins.
i. Long thin fibers, help move and support cell
ii. Move cytoplasm within the cell
(cytoplasmic streaming)
d. Ribosomes:
i. Structures where proteins are made. (one of the smallest
organelles)
1. Cells involved in protein synthesis have a ton of ribosomes
ii. Composed of RNA and proteins.
iii. Some attached to membranes, some float free in the cytoplasm
e. Endoplasmic Reticulum: (ER)
i. Complex network of channels
ii. Transports materials through the inside of the cell
iii. Lipid components of the cell membrane are assembled along with
proteins and other materials that are exported from the cell.
iv. Two different types:
1. Smooth ER:
a. Walls of the channels look smooth
b. In some cells special enzymes and chemicals are
stored here
c. Lipids are made here, and drugs are detoxified.
i. Often in liver cells
2. Rough ER:
a. Aids in the synthesis of proteins.
i. Newly made proteins are inserted here so
they can be chemically modified
ii. Most proteins that are released or exported
from the cell come from the Rough ER
b. Ribosomes are stuck to the surface to give its rough
exterior
f. Golgi Aparatus:
i. Founded by Camillo Golgi
g.
h.
i.
j.
(7:3)
III.
ii. Special compartments where proteins go to get modified by special
enzymes that attach carbohydrates and lipids to them.
iii. Collects, packs, and distributes molecules made at one location of
the cell and used at another
iv. Looks like a stack of pancakes; membranes stacked on top of one
another.
Lysosomes: (NOT IN PLANTS)
i. Small membrane bordered structures that contain chemicals and
enzymes necessary for digesting certain materials in cells, such as
lipids, carbs, and proteins.
1. Helps with endocytosis: when materials that are too large
to pass through the cell membrane get into the cell.
ii. Breaks down foreign material in order to be taken in by the cell
iii. Breaks down the organelles that are no longer useful
1. Like “clean-up crews”
Vacuoles:
i. Store water, salts, proteins, and carbohydrates
1. Saclike structure
2. In many plant cells there is a single central vacuole filled
with liquid
a. Pressure from this vacuole makes it possible for
plants to grow quickly and to support heavy
structures (leaves and flowers).
Mitochondria:
i. Organelles that change energy from one form to another –
Powerhouse of the cell
1. Change the chemical energy stored in food into compounds
that are more convenient for the cell to use.
ii. Contains two special membranes:
1. Outer membrane; surrounds it
2. Inner membrane; has many folds that help increase surface
area
a. Small Intestine has the same sort of folding for
structure.
Chloroplast: (ONLY IN PLANTS)
i. Also change energy from one form to another
1. Trap energy of sunlight and convert it into chemical energy
ii. Has three membranes
1. First two surround the chloroplast
2. Third membrane is where sunlight is changed into chemical
energy.
iii. Chlorophyll is stored here
Cell Boundaries
a. Cell Membrane:
i. Functions
1. Separates all cells from their surroundings
2. Regulates what enters and leaves the cell
3. Protects and supports the cell
a. Ex. House
ii. Structure
1. Composed of phospholipids, proteins, and carbohydrates:
lipids are the most important
a. Makes a lipid bilayer: double layer of lipids – basic
unit of membrane
i. Phospholipids: composed of hydrophilic
heads and hydrophobic tails.
1. Position themselves so that the tails
stay away from water, and the heads
are on the outside.
b. Proteins
i. Some proteins stick to surface of lipid
bilayer
ii. Others move around within the layer
1. Free-moving proteins are channels
where molecules can pass.
2. Others act like pumps pushing the
molecules from one side to another.
c. Carbohydrates
i. Attached to proteins or lipids at membrane
surface
ii. Act like chemical identification cards, allow
cells to interact and recognize each other.
b. Cell Wall: (only in plants, algae, and some bacteria)
i. Function
1. Lies outside the cell membrane, and helps to protect and
support cell
2. Water, oxygen, carbon dioxide, and other substances can
pass through it very easily (has many pores)
ii. Structure
1. Made up of two or more layers
a. First layer forms where two plant cells meet
i. Contains pectin: gluey substance that holds
cells together
ii. Forms a cell wall on pectin to separate it
from other cells called primary cell wall.
1. Primary cell wall is made up of
cellulose. This makes it elastic so it
can stretch as the cell grows.
b. Plants that have woody stems have a secondary cell
wall.
i. Composed of cellulose and lignin – makes it
more rigid
1. Ex. Wood is mostly secondary cell
walls, paper
c. How cells exchange materials (all cells are in liquid)
- some membranes are permeable (allow things to pass through) semipermeable (allow only certain sized things to pass through) or
impermeable (allows nothing to pass through)
i. Passive transport: needs no energy added to move materials into
and out of cells
1. Diffusion: movement of molecules from an area of high
concentration to an area of lower concentration.
a. Ex. Cookie smells, ink in water
b. When concentration is the same throughout it is in
equilibrium (molecules will still move, just equally
in both directions)
c. Concentration Gradient: the difference in
concentration across a distance
2. Osmosis: diffusion of water across a membrane (from high
water to low water) Pg. 185
a. Hypertonic Solution: solution has more solutes
(less water)
b. Hypotonic Solution: solution has less solutes
(more water)
c. Isotonic Solution: equal amount of solutes and
water
3. Facilitated Diffusion: move from high concentration to
low concentration, but needs a channel to fit though –
transport proteins in the membrane
a. Membrane has a gate
ii. Active Transport: required energy to allow materials to move
across a membrane against a concentration gradient. (low to high)
1. ex. Fish swimming upstream
a. Molecules carried through membrane by pumps
b. Endocytosis – taking material into the cell
membrane by means of infoldings, or pockets, or
the cell membrane. (in cell membrane section too).
i. Pocket breaks loose and forms a vacuole
ii. Large molecules, food, other cells
iii. Process called Phagocytosis: extensions of
cytoplasm surround and engulf large
particles.
c. Pinocytosis: Tiny pockets form along the cell
membrane, fill with liquid, and pinch off to form
vacuoles within the cell.
d. Exocytosis: when large amounts of material are
released from the cell.
(7:4)
IV.
Cell Specialization:
a. Cells are often uniquely suited to perform a particular function within an
organism.
i. Ex. Street sweepers, light sensitive, lysosomes
b. Levels of Organization:
i. Cells: First level
ii. Tissues: Second level; group of similar cells that perform a
function
1. muscle
2. epithelial
3. nerve
4. connective
iii. Organs: third level; group of tissues that work together to perform
a function.
iv. Organ systems: fourth level, group of organs working together to
perform a function
1. muscular system
2. skeletal system
3. circulatory system
4. nervous system
5. respiratory system
- Cells working together makes multi-cellular life possible!!!