CELLS LEC

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Cell Structure and
Function

Chapter Outline
 Cell theory
 Properties common to all cells
 Cell size and shape – why are cells so small?



Prokaryotic cells
Eukaryotic cells





Organelles and structure in all eukaryotic cell
Organelles in plant cells but not animal

Cell junctions

History of Cell Theory
 mid 1600s – Anton van Leeuwenhoek


Improved microscope, observed many living cells

 mid 1600s – Robert Hooke


Observed many cells including cork cells

 1850 – Rudolf Virchow


Proposed that all cells come from existing
cells

Cell Theory
All organisms consist of 1 or more
cells.
2. Cell is the smallest unit of life.
3. All cells come from pre-existing
cells.
1.

Observing Cells (4.1)
 Light microscope




Can observe living cells in true color
Magnification of up to ~1000x
Resolution ~ 0.2 microns – 0.5 microns

Observing Cells (4.1)
 Electron Microscopes





Preparation needed kills the cells
Images are black and white – may be
colorized
Magnifcation up to ~100,000
• Transmission electron microscope (TEM)


2-D image

• Scanning electron microscope (SEM)


3-D image

SEM

TEM

Cell Structure
 All Cells have:

an outermost plasma membrane
 genetic material in the form of DNA
 cytoplasm with ribosomes


1. Plasma Membrane
• All membranes are phospholipid
bilayers with embedded proteins
• The outer plasma membrane
isolates cell contents

controls what gets in and out of the cell
 receives signals


2. Genetic material in the
form of DNA




Prokaryotes – no membrane
around the DNA
Eukaryotes – DNA is within a
membrane

3. Cytoplasm with ribosomes




Cytoplasm – fluid area inside outer
plasma membrane and outside
DNA region
Ribosomes – make proteins

Cell Structure
 All Cells have:

an outermost plasma membrane
 genetic material in the form of DNA
 cytoplasm with ribosomes


Why Are Cells So Small? (4.2)
 Cells need sufficient surface area to allow

adequate transport of nutrients in and
wastes out.
 As cell volume increases, so does the
need for the transporting of nutrients and
wastes.

Why Are Cells So Small?
 However, as cell volume increases the

surface area of the cell does not expand
as quickly.


If the cell’s volume gets too large it cannot
transport enough wastes out or nutrients in.

 Thus, surface area limits cell volume/size.

Why Are Cells So Small?
 Strategies for increasing surface

area, so cell can be larger:
“Frilly” edged…….

Long and narrow…..


 Round cells will always be small.

Prokaryotic Cell Structure
 Prokaryotic Cells are smaller and

simpler in structure than eukaryotic
cells.
Typical prokaryotic cell is __________

Prokaryotic cells do NOT have:


• Nucleus
• Membrane bound organelles

Prokaryotic Cell Structure
 Structures







Plasma membrane
Cell wall
Cytoplasm with ribosomes
Nucleoid
Capsule*
Flagella* and pili*

*present in some, but not all prokaryotic cells

Prokaryotic Cell

TEM Prokaryotic Cell

Eukaryotic Cells
 Structures in all eukaryotic cells




Nucleus
Ribosomes
Endomembrane System







Endoplasmic reticulum – smooth and rough
Golgi apparatus
Vesicles

Mitochondria
Cytoskeleton

NUCLEUS
CYTOSKELETON
RIBOSOMES

ROUGH ER

MITOCHONDRION

CYTOPLASM

SMOOTH ER

CENTRIOLES
GOLGI BODY
PLASMA
MEMBRANE

LYSOSOME

VESICLE
Fig. 4-15b, p.59

Nucleus (4.5)
 Function – isolates the cell’s genetic

material, DNA


DNA directs/controls the activities of the cell
• DNA determines which types of RNA are made
• The RNA leaves the nucleus and directs the
synthesis of proteins in the cytoplasm at a
______________

Nucleus
 Structure


Nuclear envelope
• Two Phospholipid bilayers with
protein lined pores




Each pore is a ring of 8...
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