cells - parts
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CELLS
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Cell Theory
All things are made up of cells.
The cell is the structural and functional unitof living things.
Cells come from preexisting cells.
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Important people who contributed to
the development of the Cell Theory:
Robert Hooke - coined the term cell and wasresponsible for the beginning of the scienceofCytology.
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Anton van Leeuwenhoek- discovered
bacteria and other microorganisms in
water and studied the structure ofplant and animal cells.
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Robert Brown - discovered nucleus in
cells.
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Johannes Purkinje - introduced the
term protoplasm for the living matter of
the cell.
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Matthias Schleiden (botanist) andTheodor Schwann (zoologist) -
introduced the concept that all plantsand animals are made up of cells.
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Rudolf Virchow- found that cells
divide to form new cells. He concluded
that cells come from preexisting cells.
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Kinds of cells:
1. Prokaryotic cells - nuclear materials not well-definedand not enclosed by nuclear membrane.
* Cells divide by fission.
2. Eukaryotic cells - the nucleus is well-defined and
enclosed by a nuclear membrane.
* Cells divide by mitosis.
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Three Main parts of the Cell:
1. Cell membrane orplasma membrane -
surrounds the cytoplasm.
* in plant cells it is covered by cell wall
* consists of a double layer of fats orlipids (phospholipid) with scattered
proteins
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Cell membrane
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* protein molecules are either located
inside or merely on the surface of the
phospholipid bilayer
* protein molecules
account for the
elasticity of the
cell membrane
* differentially permeable
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Functions:
Separates the contents of the cell fromthe external environment
Regulates the passage of materials intoand out of the cell
Allows communication with other cells
Acts as receptor molecule
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Cell wall
Skeletal framework of the plant cell
Substances present:
a. cellulose complex carbohydrate
b. lignin responsible for hardening of wood
c. cutin oily substance which renders cell wallimpermeable to gases and water
d. Suberin waxy substance which renders the cellwall impermeable to gases and water
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2. Cytoplasm
A region of the cell that includesthe organelles and cytosol
Contains all the necessary
life-sustaining components of the cell
Protoplasm between the nucleus and plasmamembrane
Contains organic and inorganic compounds
Actively moving or streaming - cyclosis
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Cytosol - a thick, semi-fluid or gel-like aggregate ofchemical compounds
Two regions:* Ectoplasm - outer homogeneous portion
- also called as cortex or plasma gel
- has the ability to undergo
reversible sol-geltransformation
* Endoplasm - inner granular layer
of the cytoplasm between the
cortex and the nuclear membrane
- also called hyaloplasm
- a layer where organelles andinclusions are found
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3. Nucleus
Controls all theactivities of the cell
Contains genetic materials
Filled up with nucleoplasm or karyoplasm
Enclosed by a nuclear membrane
Site where ribosomes are formed
Stores and carry hereditary information from
one generation to another
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Nucleus of a cell
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Parts of the nucleus:
a. Nuclear membrane - encloses thenucleus
b. Nucleoplasm - protoplasm within thenucleus
c. Nucleolus - site of ribosomal production
d. Chromatin materials - active form ofchromosomes; composed of DNA
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Kinds of chromosomes:
a. Autosomes - body chromosomes;
chromosomes that affect bodily
characteristics
b. Sex chromosomes - they affect the
sex of an individual
* XY - male * XX - female
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Two groups of structures found
in the cells:
1. Organelles - living structures whichperform specific function
2. Inclusions - non-living components ofthe cytoplasm
* vacuoles, granules, pigments,crystals
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ORGANELLES:
1. Mitochondria - sites of cellularrespiration
* harness energy by breakingdown food molecules to make ATP,which is the main source of energy
of the cells
* Inner membrane is folded calledcristae
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Mitochondria
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2. Ribosomes Site of protein synthesis
Received coded message from DNA as to the
kind of protein to be synthesized
Kinds:
a. free ribosomes - suspended in the
cytosol and produce proteins that usedby the cell
b. attached ribosomes - attached to the ER;
make proteins that are secreted by the cells
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3. Endoplasmic reticulum
Consists of flattened sheets and tubes whichare attached to the nuclear membrane and
extends to the cytoplasm
Kinds:
a. Rough ER - with attached ribosomes
- involved in protein sysnthesis
- transport proteins to other locations
within the cell
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Rough ER
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b. Smooth ER - free from ribosomes
- site of fat metabolism
- in testes and adrenal cortex - it is
involved in the production of steroid
hormone
- in liver- it helps detoxify drugs
- in muscle cells - act as storage ofcalcium ions that are released when
contraction occurs
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4. Golgi apparatus
A system of flattened, membrane-bound sacs thatmove through the cytoplasm
Involved in modifying, sorting and packagingmacromolecules for secretion or for delivery to otherorganelles
Plant cell - Dictyosome - function during cell division
Increases during cell division because they formvesicles containing polysaccharides needed for cellplate formation - cell wall
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5. Lysosome
Considered the digestive sacs in the
cell
Involved in:
autophagy - digestion of cells own
materials
heterophagy - digestion of other cells
materials
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6.Peroxisomes (Glyoxisomes in
plants)
Found abundantly in cells that metabolizefats and alcohol (liver and kidney cells)
Contain oxidative enzymes (peroxidase)for oxidizing certain organic moleculesresulting in the formation of hydrogenperoxide.
It breaks down alcohol and other toxins
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7. Vaults
Discovered in 1990s
Shaped like octagonal barrels
Can dock to the nuclear pores
Pick up molecules synthesize in the nucleusand deliver to other parts of the cell
Pick up messenger RNA from the nucleusand transport it to the ribosomes for proteinsynthesis
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8. Centrioles
Found only in animal cells
Located in the middle of centrosome
Play an important role during cell
division
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9. Cytoskeleton
Network of interconnected filaments
which extends throughout the
cytoplasm
Provides structural support and
responsible for cell shape and motility
Helps in cell division
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cytoskeleton
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Kinds ofcytoskeleton:
a. Microfilaments - thinnest fibers
b. Microtubules - thickest
c. Intermediate filaments - in between
in thickness
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Microfilaments - composed of globular
protein called actin
Play an important role in muscle cells
contraction together with myosin
Intermediate filaments - reinforce in
maintaining cells shape by anchoring
some organelles
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Microtubules - composed of globularproteins called tubulins
* provides rigidity and shape of the cell
* provide anchorage for organelles
* guide the movement of chromosomeswhen cells divide
* main structural component of ciliaand flagella
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10. Plastids in plants only
Storage of pigments and starch
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Kinds of plastids:
1. Chloroplasts green colored plastids
* contain chlorophyll which are found inmembrane of sacs called thylakoids ,
stacked like coins called grana. They are
embedded in a fluid called stroma.
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chloroplasts
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2. Chromoplasts
Synthesize and store carotenoid pigments
(red, orange, yellow) and anthocyanin (red
and violet)
Develop from degenerating chloroplasts
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3. Rheodoplasts
Red pigment in tomato
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4. Leucoplasts Colorless plastids
Food storage
Abundant in roots, stems and tubers
Classes: a. amyloplasts store
starch
b. aleuroneplasts store proteins
c. elaioplasts store oils and fats
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11. Glyoxysomes
Found in leaves that are photosynthetic;and
also in germinating seeds change oil intosugar used as nutrients for growing plant
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INCLUSIONS:
1. Vacuoles contain stored pigments and
toxic substances which protect plants from
herbivorous animals
* contain watery solution called cell sap
* surrounded by a membrane called
tonoplast
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2. Fat droplets
3. Starch grains
4. crystals
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Seatwork (by group)
Draw a typical plant cell AND an animal
cell.
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