Download Unit 6

CELL
STRUCTURE
AND
FUNCTION
By: Elizabeth Wickham
CHAPTER 4:
A TOUR OF
THE CELL
"Biology is a software process. Our bodies are made up of trillions of
cells, each governed by this process. You and I are walking around
with outdated software running in our bodies, which evolved in a very
different era."
What is the
Cell Theory?
• All organisms are composed of one or more cells
• The cell is the smallest unit having the properties of life
• The continuity of life arises directly from the growth
and division of single cells
What do all
cells have in
common?
• The cytoplasm contains semifluid substance,
membrane systems, filaments, and other particles.
• A nucleus or nucleoid region which contains the
hereditary material.
• A plasma membrane which separates each cell from
the environment and allows the flow of molecules
across the membrane.
Surface-toVolume
Ratio
• Cell size is constrained by the surface-to-volume ratio.
• It states that if a cell expands its diameter during
growth, its volume will increase more rapidly than its
surface area will.
• The smaller the cell the more efficient it is but if the cell
gets to large it will not be able to move materials into
or out of the cell.
The Cell
Membrane
• A lipid bilayer forms a boundary between the inside
and the outside of the cell.
• It subdivides the cytoplasm into compartments.
• It also regulates the entry and exit of substances.
• Proteins embedded in membrane serve as channels,
pumps, or receptors.
Microscopes
• Light Microscopes use waves of light to make an
image.
– Example: Compound Light Microscope
• Electron Microscopes use magnetic lenses to bend and
diffract beams of electrons resolving details 100,000
times smaller than with Light Microscopes.
– Transmission Electron Microscopes produce
images of internal details.
– Scanning Electron Microscopes produce images of
a specimen's surface.
Prokaryotes
• Prokaryotic, meaning "before the nucleus," indicates
the existence of bacteria before the evolution of cells
with a nucleus.
• A prokaryotic cell lacks a membrane-enclosed nucleus
and membrane-enclosed organelles.
• Two domains exist: Bacteria and Archaea.
Biofilms
• Biofilms occur when single-celled organism share a
layer of polysaccharides and glycoproteins.
• They form as different species sense the presence of
other species.
• Microenvironments help to support the different
species of the community.
Eukaryotes
• Eukaryotes have a membrane-enclosed nucleus and
membrane-enclosed organelles.
• The interactions between these organelles help the cell
to function and metabolize.
• Organisms with eukaryotic cells include protists,
plants, fungi, and animals and they are called
eukaryotes.
Plant Cell vs.
Animal Cell
• The organelles that are specific to a plant cell are:
– Cell Wall
– Chloroplasts
– Central Vacuole
• Centrioles are specific to animal cells in cell division.
The Nucleus
• The nuclear envelope is a double membrane that
encloses the semifluid interior of the nucleus, called
nucleoplasm.
• In the nucleolus subunits of ribosomes (ribosomal RNA)
are prefabricated before shipment out of the nucleus.
• A chromosome is a double stranded DNA molecule.
• Chromatin is the total collection of DNA and
associated proteins.
Endoplasmic
Reticulum
• The endoplasmic reticulum is a collection of
interconnected tubes and flattened sacs that begin at
the nucleus and ramble throughout the cytoplasm.
– Rough endoplasmic reticulum has stacked,
flattened sacs with ribosomes attached.
– Smooth endoplasmic reticulum has no ribosomes
but is the area from which vesicles carrying
proteins and lipids are budded.
Vesicles
• Vesicles are transporters to and from the plasma
membrane.
• Peroxisomes are vesicles containing enzymes that
break down fatty acids and amino acids.
Vacuoles
• Animal vacuoles house debris and toxic materials in the
cell.
• The plant central vacuole accumulates a watery
solution of ions, amino acids, sugars, and toxic
substances.
Golgi Body
• In the Golgi body, proteins and lipids undergo final
processing, sorting, and packaging.
• Edges of the Golgi body break away as vesicles and
form lysosomes.
• Lysosomes digest contents of other vesicles, worn-out
parts, or bacteria and foreign particles.
Mitochondria
• Mitochondria are primary organelles that transfer the
energy in carbohydrates to ATP under oxygen-plentiful
conditions.
• They have their own DNA and ribosomes.
• Endosymbiosis is the theory that explains how
mitochondria may have been independent prokaryotic
cells that were engulfed by another cell but became
permanent, remaining with the host cell.
Chloroplasts
• Chloroplasts are specialized for photosynthesis.
• The innermost membrane, stacked disks, pigments,
and enzymes trap sunlight energy to form ATP and
NADPH.
• Chromoplasts store red and brown pigments for fall
leaves whereas colorless amyloplasts lack pigments
and store starch grains.
The Cell Wall
• The cell wall is the carbohydrate frameworks for
mechanical support in bacteria, protistans, fungi, and
plants.
• Cellulose strands form the primary wall and more
layers are deposited to form the secondary wall made
of lignin.
Extracellular
Matrix
• The extracellular matrix between animal cells includes
cell secretions and materials drawn from the
surroundings between cells such as carbohydrates and
proteins.
Cell
Junctions
• Plasmodesmata cross the adjacent primary walls and
connect the cytoplasm.
– Tight Junctions produce an effective seal when
cytoskeleton strands of one cell fuse with strands
of neighboring cells.
– Adhering Junctions help cells that need to be held
together during stretching.
– Gap Junctions are small, open channels that
directly link the cytoplasm of adjacent cells.
Cytoskeleton
• The cytoskeleton forms an interconnected tube system
of bundled fivers, slender threads, and lattices that
extends form the nucleus to the plasma membrane.
– Microtubules are composed of long tubulin cylinders and
the help in the movement of chromosomes during cell
division.
– Microfilaments consist of two helically twisted
polypeptide chains assembled form actin monomers and
are important in movements on cell surface and shape of
cell.
– Intermediate filaments are the most stable of the
cytoskeletal elements. They occur only in animal cells of
specific tissues and help to strengthen and maintain the
shape of cells or cell parts.
Lets get
moving!
• Cilia are short and provide locomotion for free-living
cells or may move surrounding water and particles if
the ciliated cell is anchored.
• Flagella are long and found on one-celled protistans
and animal sperm cells.
• Pseudopods are temporary lobes that project form the
cell and are used in locomotion and to capture food.
CHAPTER 5:
MEMBRANE
TRANSPORT AND
CELL SIGNALING
"Life evolved under conditions of light and darkness, light and then darkness. And so plants
and animals developed their own internal clocks so that they would be ready for these changes
in light. These are chemical clocks, and they're found in every known being that has two or
more cells and in some that only have one cell."
Phospholipid
Bilayer
• If the phospholipid molecules are surrounded by water,
their hydrophobic fatty acid tails cluster and the
hydrophilic heads face outward forming a bilayer.
• Cell membranes are composed of:
– Phospholipids
– Steroids
– Proteins
• Carbohydrates attach to cell membranes in different
ways for different cells.
• Fatty acid tails of membrane phospholipids vary in
length and saturation.
Protein
Orientation
• Peripheral proteins are positioned at the surface of the
membrane.
• Integral proteins span the lipid bilayer, with their
hydrophilic domains extending past both surfaces.
Membrane
Proteins
• Adhesion proteins help cells stay connected to one
another in a tissue.
• Recognition proteins identify certain cell type, guide
cells to becoming tissues, and cell to cell recognition
and coordination.
• Receptor proteins have binding sites for hormones that
can trigger changes in cell action, as in growth process.
• Enzymes help to accelerate reactions without being
changed themselves.
• Transport proteins passively allow water-soluble
substances to move through their interior, which opens
on both sides of the bilayer.
– Passive transporters require no energy.
– Active transporters use ATP to pump substances.
A Permeable
Membrane
• Cells keep extracellular fluid contents separate form
the contents of the cell with membranes that are
selectively permeable.
Concentration
Gradient
• A concentration gradient refers to the difference in the
number of molecules (or ions) of a substance in a given
volume of fluid between two adjoining regions.
Diffusion
• In the presence of a concentration or electrochemical
gradient, diffusion results in the net movement of a
substance form a region where it is more concentrated to
a region where it is less concentrated.
• Facilitated diffusion is the passage of molecules or ions
down their electrochemical gradient across a biological
membrane with the assistance of specific transmembrane
transport proteins, requiring no energy.
• Factors that influence the rate and direction of diffusion:
– Size
– Temperature
– Steepness of the concentration gradient
– Charge
– Pressure
• Dynamic equilibrium is reached when gradients no longer
exist and there is no net movement.
Passive and
Active
Transport
• In passive transport a concentration gradient and/or
electric gradient drive diffusion of a substance across a
cell membrane through a transport protein – a passive
process expending no energy that continues until
concentration gradients are equal on both sides.
• Active transport moves ions and large molecules across
a membrane against a concentration gradient and
special proteins are induced to change shape, but only
with an energy boost form ATP.
Exocytosis
and
Endocytosis
• In exocytosis cytoplasmic vesicles move substances
from the cytoplasm to plasma membrane where the
membranes of the vesicles and cells fuse.
• Endocytosis encloses particles in small portions of the
plasma membrane to form vesicles that then move
into the cytoplasm.
– Phagocytosis
– Receptor-mediated endocytosis
– Bulk-phase endocytosis
Osmosis
• Osmosis is the passive movement of water across a
differentially permeable membrane in response to
solute concentration gradients, pressure gradients or
both.
– Hypotonic Fluid – lower concentration of solutes
than the fluid in the cell (cause it to swell).
– Hypertonic Fluid – higher concentration of solutes
than the fluid in the cell (cause it to shrink).
– Isotonic Fluid – the same concentration of solutes
as the fluid in the cell (no movement occurs).
Pressure
• Cells are either in a constant environment or adapted
to a hypotonic or hypertonic one.
• Hydrostatic pressure increases the greater the solute
concentration is.
• Hydrostatic pressure is countered by osmotic pressure
which prevents any further increases in the volume of
the solution.
THE END is near...