Download plasma membrane

Looking at Cells
Microscopes: A basic biology tool that allowed
for the discovery of cells and cell parts.
 Simple microscope- hand lens
 Compound microscope- uses 2 or more
lenses working together. The maximum useful
magnification is 1200-1500x.
 Electron microscope- uses an electron beam
in place of light. These can magnify over
500,000x or half a million times.
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Electron Microscopes
SEM- scanning electron microscope- used
to view surfaces like cell walls and cell
membranes.
 TEM-transmission electron microscopemore powerful- used to study tiny
structures and organelles inside of cells.
 STM-scanning-tunneling microscope is
used to view the structure of large
molecules.
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Organelles
Organelle- a structure inside a cell that is surrounded
by a membrane. Each organelle has a specific function
or job.
 Membrane- covering around cells or organelles. They
have several functions:
 1. Membranes surround a cell or organelle and define
its space. Separates living materials from the
environment.
 2. Membranes control materials that come and go from
cells or organelles.
 3. Serve to protect.
 4. Membranes are made mostly of lipids.
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2 Types of Cells
Prokaryotes- Kingdoms Eubacteria and
Archebacteria- all the bacteria, all the
archebacteria and blue-green algae. The cells
have no organelles & no nucleus.
 All the cell chemistry is carried on in the cells
cytoplasm. DNA floats in the cytoplasm in long
strings or coils.
 Eukaryotes: have internal membrane covered
organelles. Also have a nucleus where DNA is
found during most of the cells life. Kingdom
Plantae, Animalia, Fungi and Protista are
eukaryotes.
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Scientists of Cells
Robert Hooke- English- used microscope to view cork
wood. Coined the term “cell”.
 Anton van Leeuwenhoek- Dutch- mid 1600’s, An
eyeglass lense grinder who built microscopes and used
them, The first scientist to describe living cells as seen
through a simple microscope
 Robert Brown- first wrote about the cell nucleus.
 Rudolf Virchow first predicted that the nucleus
contained genetic material and was responsible for cell
reproduction.
 Matthias Schleiden- German, 1830’s, proposed that all
plants were made of cells.
 Theodore Schwann- German, 1830’s, proposed that
all animals are made of cells.
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Cell Theory
Cell Theory- A cornerstone of modern
biology! It has 3 Parts
 1. All living things are made of cells.
 2. The cell is the basic unit of life.
 3. All cells come from other living cells.
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Hierarchy of organization in
living things:
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Cells Tissues Organs Organ Systems Organism
Cells of similar function combine to form tissues:
nerve tissue, muscle tissue, meristem tissue in
plants.
 Two or more tissues form an organ: muscle, nerve
and epithelial tissue form the heart.
 Two or more organs form an organ system:
stomach, liver, small intestine, teeth are parts of the
digestive system.
 An organism is several systems working together: a
human and other vertebrates are made of 11
systems.
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Plasma Membrane
The plasma membrane has several functions:
 1. It surrounds the cell material and defines the
cells space.
 2. It separates the cell from the surrounding
environment.
 3. It controls the movement of materials into
and out of the cell. This helps maintain a
balanced living condition. (Homeostasis)
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Plasma Membrane
The plasma membrane is made of 2 layers of
lipid with proteins inserted here and there. This
is referred to as a “lipid bilayer”. The lipids also
have phosphate groups attached so they are
referred to as “phospholipids”.
 The inserted proteins are sometimes known as
transport proteins because they help move
materials across the membrane.
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Membrane Crossing
Things that must cross the plasma
membrane:
 Water, oxygen, waste products, glucose,
food, carbon dioxide are some things that
must commonly cross the plasma
membrane.
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Osmosis- the movement of water along a
concentration gradient
High
concentration
Equal
concentration
Low
concentration
Fluid Mosaic Theory
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The theory of the fluid mosaic model describes
the structure of the plasma membrane and
explains how and why it functions as it does.
Each cell membrane is composed of 2 opposing
layers of phospholipids.
Each phospholipid molecule has a polar (water
soluble) which is a phosphate.
This is also called the hydrophilic or water loving
end.
The other end of the phospholipids is made of
nonpolar (oil soluble) fatty acids. This is the
hydrophobic or water hating end.
These phospholipids in the membrane line
themselves up with the polar phosphates
facing outward toward the water soluble
environment and facing inward toward the
water soluble inside of the cell.
 The nonpolar or hydrophobic ends of the
phospholipids move into the middle of the
membrane where there is no water.
 Cholesterol molecules are found in
between phospholipid molecules in the
membrane. Cholesterol keeps the
membrane liquid and allows the
phospholipids molecules to move around.
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Two Types of proteins
Transport proteins are found sticking thru the
plasma membrane and allow movement of
particles across the membrane. 2 types:
 1. Channel proteins-these form openings that
allow material dissolved in water to pass thru.
This allows passive transport of sugars, amino
acids and ions to cross the membrane. This
simply forms an opening that allows these
materials to move thru.
 2. Carrier protein- A protein molecule in the
membrane that physically attaches to a molecule
or particles and pulls or pushes it thru the
membrane. A form of active transport.
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Eukaryotic Cell Structure
Cell walls: A solid covering around cells
of plants, fungi, bacteria and some
protests. No animal cells have cell walls.
 It provides support and physical protection
for the cell. It DOES NOT control
movement of materials into or out of the
cells.
 Trees are able to grow to large heights
because of the support given to their cells
by cell walls. Plants cell walls contain
cellulose as the main structural material.
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Nucleus
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Nucleus: A fairly large membrane covered organelle
that controls the cell. It has several parts: all materials
in the nucleus are referred to as nucleoplasm.
1. nuclear membrane or nuclear envelope
surrounds the nuclear material and controls the
movement of materials into the nucleus.
2. Chromatin- unwound DNA fibers inside the
nucleus. The DNA contains the genetic code for all the
cells proteins. During cell division, chromatin coils up
into short spools called chromosomes.
3. Nucleolus- A small membrane covered area
INSIDE the nucleus that builds ribosomes for the cells.
Ribosomes build proteins for the cell.
Ribosomes
The sites of protein synthesis.
 Makes proteins based on RNA instructions.
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Cytoplasm- a jelly like mixture of water,
proteins, Chemicals, and organelles that
make up all the cell except the nucleus.
There are several organelles.
 The clear fluid inside the cell.
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ER
1. Endoplasmic reticulum- layers of manyfolded membranes that act as transport canals.
These folded membranes act as sites for many
chemical reactions. Many ribosomes are found
on the ER, so lots of protein synthesis occurs
there.
 A folded membrane that forms a network of
interconnected compartments in the cytoplasm
 Smooth ER-areas with no ribosomes.
 Rough ER- areas with ribosomes.
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Golgi bodies
Golgi bodies- similar in structure as the
ER. These “package” protein molecules
that must be excreted from the cell. This
packaging allows the molecule to cross
thru the cells plasma membrane. Golgi
bodies are very numerous and active in
cells that secrete proteins such as glands
and digestive organs.
 Closely stacked, flattened membrane sacs.
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Vacuoles
Vacuoles- storage areas. Can store food,
chemicals, starches, proteins, almost
anything. Plant cell often have very large
vacuoles.
 A membrane-bound, fluid-filled sac.
 Provides temporary storage of food,
enzymes, and waste products
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Lysosomes
Lysosomes- special vacuoles that that
breakdown or digest old, worn out
organelles or food particles.
 This allows the cell to recycle materials.
 Digest excess or worn-out cell part, food
particles, and invading viruses or bacteria
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Mitochondria
Mitochondria- found in all eukaryotic cells,
these break down sugars and release energy. It
has a highly folded inner membrane that serves
as a “workbench” for enzymes. Cells that
require a lot of energy will have many
mitochondria. Liver cells may have 2500 each.
 The structure of chloroplasts and mitochondria
are very similar, but their function is directly
opposite: chloroplasts build sugars, mitochondria
break sugars apart.
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Endosymbiontic Theory
Endosymbiontic theory- proposed in the
1960’s by Lynn Margulis (p.392). The theory
proposes that eukaryote cells evolved as a result
of a symbiotic relationship between several
types of prokaryote cells.
 In other words, organelles such as chloroplasts
and mitochondria were once free living
prokaryotes, but became absorbed into a larger
prokaryote to form a eukaryote cell.
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Cytoskeleton
Cytoskeleton- a network of thin fibers that
give support, shape and structure to a cell.
There are 2 types of support materials:
 1. microtubules that are thin, hollow protein
tubes.
 2. microfilaments that are thin, solid protein
fibers.
 Imagine the cytoskeleton as the poles of a tent.
It holds up the tent cover (plasma membrane)
and provides space inside the tent.
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Cell Wall
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Firm, protective structure that gives the
cell its shape in plants, fungi, most
bacteria, and some protists.
Chloroplasts
Chloroplast- found in plants, and some
protests and some bacteria. This allows the cell
to trap the energy in sunlight to power a food
making process called photosynthesis. These
contain the chemical chlorophyll which is a
green pigment that actually traps the light
energy. It has 2 major parts :
 1. The granum- which looks like stacks of coins
surrounded by a membrane. Each “coin” is
called a thylakoid. It is in the thylakoid that
Grana
light energy is trapped.
 2. The stroma- a fluid that surrounds the grana
in the chloroplast.
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Locomotion
Flagella- a long tail like structure that is used
as a “paddle” to move a cell thru water. A cell
can have 1 or more of these.
 Cilia- a short hair like structure that is used as a
locomotion device (movement). Usually a cell
will have many of these. Some body cells in
animals have cilia on their surface so that as the
cilia move, particles can be moved around in the
organism.
 Cilia cells in your respiratory system help move
materials such as dust out of your lungs and into
you throat. This helps keep the lung area clean.
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