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Ch 6 - A Tour of the Cell
All organisms are made of cells
• The Cell Theory:
– All living things are made of cells
– Cells are the basic unit of structure &
function in living things
– All cells come from pre-existing cells
Organelle: a cell part/structure with a
specific job/function
Cell Structures & Functions
• Structures in the nucleus:
– Nucleus: control center for the cell, made
of proteins, enzymes, & nucleic acids;
houses the cell’s genetic material & directs
cell activities
– Nuclear envelope/membrane: a semipermeable double membrane which
encloses the nucleus & regulates which
substances (molecules) enter and/or leave
the nucleus
– Nucleolus: provide materials to produce
the ribosomes
Cell Structures & Functions
• Structures in the nucleus:
– Chromosomes: made of DNA & contain
the instructions for everything the cell
makes; long strands composed of
nucleotides, which contain the coded
instructions for the accomplishment of
everything the cell makes & does
– Nucleic acids: organic compounds found
inside & outside of nucleus of cells that
carries instructions for cellular activity; DNA
& RNA are types of nucleic acids
Cell Structures & Functions
• Structures outside the nucleus:
– Cytoplasm: the combination of all the liquids,
substances, & structures between the plasma (cell)
membrane & the nucleus; consists of various
organelles suspended in the fluid outside the
nucleus
– Cell/Plasma membrane: the membrane that’s the
outer boundary of the cytoplasm; it is semipermeable & regulates the entry and/or exit of
molecules between the cytoplasm & outside
environment of the cell; a phospholipid bilayer
containing proteins that form specific functions such
as chemical reactions, cell-to-cell communication &
cell signaling, and transport of materials
Cell Structures & Functions
• Structures outside the nucleus:
– Endoplasmic reticulum (ER): the internal
transportation system of the cell; a network
of microscopic channels or canals formed
from the cell membrane spreading
throughout the cytoplasm
– Ribosomes: small spherical structures
composed of RNA (from the nucleolus);
found on the rough ER & assemble proteins
Cell Structures & Functions
• Structures outside the nucleus:
– Mitochondria: powerhouse of cell; release
energy from sugars & other molecules (active
cells such as muscle contain many of these);
small oval or rod-shaped structures in the
cytoplasm within which potential energy is
converted to kinetic energy
– Lysosomes: membrane-bound sacs that
contain enzymes; which are used to break down
macromolecules into smaller molecules
(digestion); destroy harmful bacteria; used to
recycle cell parts
Cell Structures & Functions
• Structures outside the nucleus:
– Golgi apparatus: the packaging & distribution
center of the cell; modifies, stores, & routes
proteins & other chemical products to their next
destinations (like a factory or post office); a
system of storage chambers for molecules
made within the cell but which are to leave the
cell to be used somewhere other than in the
cell that produced them
Cell Structures & Functions
• Structures outside the nucleus:
– Vesicles: small membrane sacs that specialize
in moving products into, out of, & within the cell
– Chloroplasts: contain chlorophyll; is the site of
photosynthesis, the chemical process which
packages the energy of the sun into a
carbohydrate (sugar) molecule; in plant cells
only
– Cell wall: made of cellulose; is produced by
the cell for protection & strength; located
immediately next to the outer surface of the
cell membrane of plants only
Cell Structures & Functions
• Vacuoles: membrane-bound spaces (bag-like
structures) found in the cytoplasm including the
following:
– Food Vacuole: stores particles of food
– Water vacuole: stores water & may act as a kind of
“pump” to force excess water out of cell
– Digestive vacuole: encloses particles of food &
chemically breaks down food molecules
– Waste vacuole: contains useless leftover
molecules from the digestive process
– Contractile vacuole: pumps out excess water that
diffuses into single-celled organisms; keeps them
from bursting
• Prokaryotic cell: cells without a nucleus or
membrane bound organelles; bacteria
• Eukaryotic cell: cells with a nucleus and
membrane bound organelles;
us/animals/plants
Cell Posters Next!
Pro vs. Eu
• Eu =
True
• Pro =
earleir
than
Membranes organize a cell’s activities
• Cell membrane - Like security guard - controls flow of
materials into & out.
• Phospholipid - Basic building block of membranes
- Type of lipid w/ polar head & nonpolar tail
- Head - phosphorus & Nitrogen - POLAR
• Phospholipid Bilayer - Phospholipids aligned in 2
layers
- Polar heads point toward water
2 Important Characteristics of Membranes
1. Most polar molecules cannot cross.
- Interior of membrane is barrier
- Passageways of protein (“gates”)
- Regulate what enters and leaves.
2. Phospho. & Proteins not fixed in place.
- Mem. structured to fit needs of diff. cell types.
3 PROTEINS IN MEM. - Channels, Receptors,
and Markers.
•
CHANNELS (transport) - Doughnutshaped. - Needed molecules & ions cross
mem. through these.
•
RECEPTORS – Boulders - Convey info.
from external environment.
•
MARKERS - Elongated w/ chains of
carbs. - “Name Tags”
• Proteins bend, fold, twist. Shape determines
function.
Functions of Membrane Proteins
Cell Membrane
Membrane Proteins have 3 Sections
- 2 ends contain polar A.A. - form H-Bonds w/ water.
- Middle - nonpolar A.A. anchored into membrane,
remains mobile.
End of 10/29
Membranes regulate the traffic
of molecules.
• Diffusion – net movement of substances from high to low
concentration.
• Equilibrium – Balance. Movement is =
outside to inside
Passive Transport
• Passive – no Energy used. Ex: H2O
• Facilitated diffusion – Transport proteins used as
a pathway for diffusion (= to help). Ex: sugars
• Osmosis – Passive Transport (diffusion) of H2O
across selectively permeable membrane.
– Hypertonic – solution w/ higher concentration (shrinks)
Otonic – solution w/ lower concentration (swells)
– Hyp
– Isotonic – concentrations = (no change)
How do different solutions affect plant & animal cells?
Active Transport
• Energy required to move molecules.
- move from low to high concentration
(against natural flow); Ex: ions
• Endocytosis vs. Exocytosis
End of 11/1
Journal – 11/14/11
30% H20
70% Salt
50% H20
50% Salt
Beaker
Why are cells so small?
• It has everything to do with surface area
and volume
• Surface area: the measure of how much
exposed area a solid object has (in squared
units)
• Volume: how much space a 3D object takes
up (in cubed units)
Why are cells so small?
• Gases and food molecules dissolved in
water must be absorbed and waste
products must be eliminated
• For most cells, this passage of all
materials in and out of the cell must occur
through the plasma membrane
• Each internal region of the cell has to be
served by part of the cell surface. As a cell
grows bigger, its internal volume enlarges
and the cell membrane expands
Why are cells so small?
• As a cell gets larger, the volume of the
cell increases more rapidly than the
surface area (if the cell maintains its
same shape)
• Because the volume increases more
rapidly than does the surface area, the
relative amount of surface area
available to pass materials to a unit
volume of the cell steadily decreases
Video
Why are cells so small?
• Everything the cell needs or has to get rid of has to go
through the cell membrane, the amount of which
relates to the surface area. The cell's ability to either
get substances from the outside or eliminate waste is
related to the surface area
• How much food and other material from the outside
and how much waste the cell has to get rid of, is
related to the volume
• Therefore, as a cell gets bigger there will come a time
when its surface area is insufficient to meet the
demands of the cell's volume and the cell stops
growing!