cells - parts

8/8/2019 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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cells - parts

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