Download What is a Cell?

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adult human
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diameter of DNA
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Quick Review:
• Where does most of the cell's work take place?
Cytoplasm
• What happen to the proteins once they leave
the golgi apparatus and enter the cytoplasm?
• become plasma membrane protein,
• stay in the cytoplasm for use in the cell,
• stored in vesicles until needed for transport.
What is a Cell?
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Cell: basic or smallest living unit of life of
a living organism.
Protoplasm: complex jelly-like substance.
70% is water; rest is mineral salts,
proteins, carbohydrates, fats.
Made up of 3 main parts:
(i) Cytoplasm
(ii) Cell surface membrane
(iii)Nucleus
(i) Cytoplasm
•
Part of the protoplasm between cell
membrane & nucleus
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Jelly-like fluid in which many chemical
reactions or cell activities take place.
•
90% water; enzymes, organelles
(specialized structures)
nuclear pore
chromatin (DNA)
nucleus
nucleolus
nuclear envelope
flagellum
rough endoplasmic
reticulum
cytoplasm
plasma
membrane
ribosome
smooth endoplasmic
reticulum
Golgi
complex
free ribosome
vesicle
mitochondrion
vesicle
(ii) Cell surface membrane
• Partially-permeable membrane
• Controls movement of substances into and
out of the cell.
• Allows only some substances to cross it.
(e.g. small molecules: glucose, water, O2,
CO2
- prevents larger molecules from crossing:
starch, proteins
An electron micrograph of a cell membrane
(of a human red blood cell) seen in cross-section.
• made of proteins and fats
• double phospholipid layers
(fats, proteins, phosphate groups)
(iii) Nucleus
• Parts of a nucleus:
- Nuclear envelope, nucleoplasm, nucleolus
• Nucleoplasm: dense material inside nucleus
• Nucleolus(1) or nucleoli (2): Making proteins.’
• Control cell activities
e.g. cell growth, repair of worn-out parts.
• Essential for cell division.
nuclear
envelope
nucleolus
nuclear
pores
chromatin
• Chromatin: Network of long, thread-like structures
• Contains hereditary material (DNA and proteins),
instructions for the cell to carry out all chemical
reactions
• Controls cell division
• Chromosomes: when chromatin threads condense
and become highly coiled during cell division (rodshaped)
Plant cells – Cell Wall
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Non-living layer
Made up of Cellulose (a complex sugar)
Surrounds cell membrane of plant cell
Fully permeable to water, gases, dissolved
substances
Protects the plant cell from injury
Supports and gives a fixed shape to plant cell
Membrane Network –
Endoplasmic Reticulum (ER)
rough endoplasmic reticulum
ribosomes
0.5 micrometers
smooth endoplasmic reticulum
0.5 micrometers
vesicles
Endoplasmic reticulum
• 2 types: rough and smooth
• For synthesis and transport of substances
• Rough ER (RER): ribosomes are attached on
outer surface
• Continuous with nuclear envelope
• Transports proteins made by ribosomes to
Golgi Apparatus for secretion out of the cell.
Endoplasmic reticulum
• Smooth ER (SER): no ribosomes attached on
outer surface
• Makes substances – fats, steroids (sex
hormones in mammals)
• Detoxification – converts harmful
substances into harmless materials.
Ribosomes
• Small round structures
• Needed to make proteins in the cell
• 1. Attached to RER membrane – make
proteins that are transported out of
the cell
• 2. Free ribosomes in the cytoplasm –
make proteins that are used within
cytoplasm of the cell
Golgi Apparatus
• Stack of flattened spaces surrounded by
membranes
• Vesicles: tiny round structures enclosed by a
membrane
• Fuse on one side and pinch off from opposite
side of Golgi apparatus
• Stores and modifies substances made by
ER
• Packages the substances in vesicles for
secretion out of the cell
ORGANELLES
MITOCHONDRION
(mitochondria):
• “Power house” of a cell
• Aerobic respiration: food substances are oxidized
to release energy
• Energy is used for cell activities e.g. growth,
reproduction, movement etc.
PLANT CELLS - Chloroplasts
• Oval shaped structures
• Contain green pigment chlorophyll
• Absorbs sunlight for photosynthesis, for plants
to make food
ORGANELLES
VACUOLES
• Fluid-filled space enclosed by membrane
• Storage of various substances
• Animal cells: many small vacuoles; store water,
food. Exist temporarily
• Plant cells: one large, central vacuole, filled
with cell sap, contains dissolved substances
e.g. sugars, mineral salts, amino acids, helps
to maintain shape of plant cell
• Membrane – tonoplast
mitochondrion
chloroplast
Golgi complex
central vacuole
smooth endoplasmic
reticulum
vesicle
cell wall
rough endoplasmic
reticulum
plasma
membrane
nucleolus
nucleus nuclear pore
chromatin
nuclear envelope
ribosomes
free ribosome
ORGANELLES
CENTRIOLES
• Small, hollow cylinders.
• Found as a pair near the nucleus.
• Play an important part in cell division.
• Only in animal cells. Absent in plant cells.
Differences between plant and animal cells
Feature
Cell wall
Plant cell
Cell wall present
Animal cell
Cell wall absent
No. and size of 1 large permanent
vacuoles
vacuole
Numerous small
vacuoles
Relative size
Large
Small
Chloroplast
Chloroplasts present
Absent
Shape
Regular, elongated,
cylindrical
Centrioles absent
Irregular
Centrioles
Centrioles present
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