Download Cell Organelles PPT - Gulfport School District

Cell theory was the first unifying theory of
biology:
• Cells are the fundamental units of life.
• All organisms are composed of cells.
• All cells come from preexisting cells.
Most cells are tiny, in order to maintain a
good surface area-to-volume ratio.
The volume of a cell determines its metabolic
activity per unit of time.
The surface area of a cell determines the
amount of substances that can enter or
leave the cell.
Figure 4.2 Why Cells Are Small
As cells grow larger, metabolic activity and
need for resources and rate of waste
production increases faster than surface
area.
Some large cells increase surface area by
folds in the cell membrane.
The cytoskeleton:
• Supports and maintains cell shape
• Holds organelles in position
• Moves organelles
• Involved in cytoplasmic streaming
• Interacts with extracellular structures to
anchor cell in place
The cytoskeleton has three components with
very different functions:
• Microfilaments
• Intermediate filaments
• Microtubules
Microfilaments:
• The thinnest microfilaments and most
prevalent at the edge of the cell
• Anchor the cytoskeleton to integral
proteins in the plasma membrane
• Help a cell or parts of a cell to move
• Determine cell shape
• Composed of actin and myosin
• Provide mechanical support for microvilli
Microvilli - non-moving, microscopic
fingerlike projections of the plasma
membrane that increase the surface area
of the cell membrane
Intermediate filaments:
• Intermediate in size
• At least 50 different kinds in six molecular
classes
• Anchor cell structures in place
• Resist tension, maintain rigidity and found
in parts of the cell subject to mechanical
stress
Microtubules:
• Thickest cytoskeleton elements.
• Form a rigid internal skeleton for some
cells or regions
• Act as a framework for motor proteins to
move structures in the cell
Cilia—short, usually many present; move
stiffly to propel a cell, or move fluid over a
stationary cell
Flagella—longer, usually one or two present;
move the entire cell by wiggling in a wavelike pattern.
Ribosomes translate the nucleotide
sequence of a messenger RNA molecule
into a polypeptide.
Each subunit consists of ribosomal RNA
(rRNA) bound to smaller protein molecules.
Ribosomes are not membrane-bound
organelles.
In eukaryotes, they are free in the cytoplasm,
attached to the endoplasmic reticulum, or
inside mitochondria.
The endomembrane system includes the
nuclear envelope, endoplasmic reticulum,
Golgi apparatus, and lysosomes.
Tiny, membrane-surrounded vesicles shuttle
substances between the various
components, as well as to the cell
membrane.
Endoplasmic reticulum (ER)—network of
interconnected membranes in the cytoplasm,
with a large surface area
Two types of ER:
• Rough endoplasmic reticulum (RER)
• Smooth endoplasmic reticulum (SER)
Rough endoplasmic reticulum (RER) has
ribosomes attached to its outer surface.
Newly made proteins enter the RER lumen
where they are chemically modified and
tagged for delivery to specific locations.
The proteins are transported in vesicles that
pinch off from the ER.
All secreted proteins and most membrane
proteins pass through the RER.
Polypeptides are transported into the RER
lumen as they are being synthesized.
In the lumen they are folded into their tertiary
structures.
Many are linked to carbohydrate groups,
becoming glycoproteins.
Many glycoproteins are important in
recognition and interactions between cells.
Smooth endoplasmic reticulum (SER)—
more tubular, no ribosomes
• Chemically modifies small molecules such
as drugs and pesticides
• Site of glycogen degradation in animal
cells
• Site of synthesis of lipids and steroids
• Stores calcium ions, which trigger many
cell responses
Golgi apparatus: flattened sacs (cisternae)
and small membrane-enclosed vesicles.
• Receives proteins from the RER and can
further modify them
• Concentrates, packages, and sorts
proteins
• Adds carbohydrates to proteins
• Site of polysaccharide synthesis for plant
cell walls
Golgi apparatus has three regions:
• cis region: receives vesicles containing
proteins from the ER
• trans region: vesicles bud off from the
Golgi apparatus and travel to the cell
membrane or to lysosomes
• medial region: in between trans and cis
regions
Primary lysosomes originate from the Golgi
apparatus.
They contain hydrolases (digestive enzymes),
and are the site where macromolecules are
hydrolyzed into monomers.
Macromolecules may enter the cell by
phagocytosis—part of the cell membrane
encloses the material and a phagosome is
formed.
Phagosomes then fuse with primary
lysosomes to form secondary lysosomes.
Enzymes in the secondary lysosome
hydrolyze the food molecules.
• Autophagy – process by which worn out
organelles are digested by lysosomes
• Autophagosome – The name of the
vesicle created when the organelle to be
digested is enclosed by a membrane from
the ER. This will fuse with a lysosome.
• Autolysis – destruction of the entire cell by
lysosomes
Other organelles perform specialized functions.
Peroxisomes similar to lysosomes but smaller
(also called microbodies.) Oxidize various
organic substances which can be toxic like fatty
acids & alcohols. A by-product of this oxidation
is peroxide which can also be toxic. So they
also contain catalase which decomposes
peroxide. They can self-replicate or be made
from scratch.
Proteasomes – barrel shaped and consist of 4
stacked proteins around a central core. These
organelles digest and recycle used or damaged
proteins in the cytosol. They contain large
amounts of proteases.
In eukaryotes, breakdown of energy-rich
molecules begins in the cytosol.
The partially digested molecules enter the
mitochondria, where chemical energy is
converted to energy-rich ATP.
Cells that require a lot of energy often have
more mitochondria.
Mitochondria have two membranes:
• Outer membrane—very porous
• Inner membrane—extensive folds called
cristae increase surface area
The fluid-filled matrix contains enzymes, DNA,
and ribosomes.
Apoptosis – programmed cell death in
response to cell damage, excess free
radicals or DNA damage. Mitochondria
initiate the process by releasing cytochrome
c.
The nucleus is usually the largest organelle:
• Location of DNA and DNA replication
• Site where DNA is transcribed to RNA
• Contains the nucleolus (pl. nucleoli),
where assembly of ribosomes from RNA
and proteins begins
The nucleus is surrounded by two membranes
that form the nuclear envelope.
Nuclear pores in the envelope control
movement of molecules between nucleus
and cytoplasm.
In the nucleus, DNA combines with proteins to
form chromatin in long, thin threads called
chromosomes.
Gene’s are the cells smaller hereditary units.
There are many genes on individual
chromosomes.
The outer membrane of the envelope is
continuous with the endoplasmic reticulum.
Somatic cell – an cell of the body that is not a
germ cell
Germ cell – a gamete or any cell destined to
become a gamete
Interphase:
 G1 Phase – normal cell function time
 S Phase – DNA replicated
 G2 Phase – organelles replicated
• Mitotic Phase- 4 stages during which nucleus
divides
• Cytokinesis