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The Living Cell
Chapter 21
Great Idea:
Life is based on chemistry, and chemistry takes
place in cells
Chapter Outline
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The Nature and Variety of Cells
How Does a Cell Work?
Metabolism: Energy and Life
Cell Division
The Nature and
Variety of Cells
The Cell Theory
• All living things are composed of cells
• The cell is the fundamental unit of life
• All cells arise from previous cells
Observing Cells:
The Microscope
How Does a Cell Work?
Cell Membranes
• Cell Membranes
– Isolate cell
– Separates cell parts
• Transport
– Individual molecules
– Specific materials
• channels
• Receptors
– Bind molecules
• Cell Wall
– Plants
Plant Cell
There are two types of cells on Earth: Prokaryotic and
Eukaryotic. The former appeared first, and strong evidence
indicates that the latter evolved from the former via
endosymbiotic relationship.
Prokaryotic cells include all bacteria and the blue-green
algae. Fossil evidence shows that they have lived on earth
for at least 3.8 billion years.
The DNA in prokaryotic cells is not enclosed within a
membrane-bound nucleus as is the DNA in eukaryotic
cells.
Schematic of a Eukaryotic Cell
The information required for producing all of the
constituents of a cell is contained in the DNA in the
chromosomes in the nucleus
The Nucleus
• Nucleus
– Contains genetic material
• Prokaryotes
– No nucleus
• Eukaryotes
– Nucleus
• Double Membrane
Cell, the factories of life
• You have about 10 trillion cells.
• Factories have:
– Front office- paperwork
– Building- Bricks and Mortar- loading
docks
– Production Units
– Power Plant
Cell, the factories of life
• Paperwork- the plan- DNA
• Building- cell walls.
– Protein & Receptors- loading dock
Cell, the factories of life
• Production- organelles- perform the
chemical functions
• Power Plant- Mitochondria receive
carbohydrates, fats and proteins and “burn”
to produce energy
• Synthesis- site of protein synthesis
(controlled by RNA next chapter)
Photograph of a cell of maize rust. The dark
boundary is the cell wall, made from cellulose.
The nucleus takes up almost half the area of
the central part of the cell.
Mitochondria
• “Sausage“ shaped organelles (specialized
structures in cells) where molecules derived
from glucose react to produce the cells
energy
An organelle- mitochondria.
The Energy Organelles:
Chloroplasts and Mitochondria
• Organelle
– Specialized structure in cell
• Chloroplasts
– Energy transformation
• chlorophyll
– Plant cells only
– Double membrane
• Mitochondria
– Produces cells energy
– Double membrane
– Own DNA
Cytoskeleton
• Cytoskeleton
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Gives cell shape
Anchors
Allows movement
Transport system
• Within cell
• Structure
– Strong filaments
– Complex web
Metabolism: Energy and Life
Cells Energy
• Cells store energy in various ways.
• The most common is in a molecule
adenosine triphosphate or ATP.
• Making ATP is endothermic so cells can
make ATP and then release that energy
when it’s needed.
The Cell’s Energy Currency
• Adenosine triphosphate (ATP)
– Provides energy
• Structure
– 3 phosphate groups
– Sugar molecule:
ribose
– adenine
• Function
– Removal of phosphate group provides energy
The ATP reaction
ATP  ADP + PO4 + energy
The tri-phosphate becomes a di-phosphate
Photosynthesis
• Photosynthesis
– Convert sunlight to energy
• Process
– Energy + CO2 + H2O carbohydrate + O2
• Colors
Glycolysis: The First Step in
Energy Generation in the Cell
• Respiration
– Oxidation of carbohydrate
– Retrieves energy in glucose
– Aerobic
• Process
– Glycolysis
• Split glucose
• Result
– Pyruvic acid
– 2 ATP
– 2 energy carriers
• Convert energy carriers to 2-3 ATP
– 1 molecule glucose = 6-8 ATP
Fermentation: A Way to
Keep Glycolysis Going
• Fermentation
– Anaerobic
– Inefficient
• Yeast
– alcohol
• Animal cells
– Lactic acid
The Final Stages
of Respiration
• Krebs cycle
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Glucose broken down
CO2 produced
ATP
Energy-carrying molecules
• Result
– 36-38 ATP
Cell Division
Mitosis
• Mitosis
– Cell division
– Not for sexual reproduction
• Chromosomes
• Process
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Copy chromosomes
Spindle fibers
Migration of chromosomes
Nuclear membrane reforms
Meiosis
• Meiosis
– Sexual reproduction
– 1 cell forms 4 gametes
• Gametes are genetically unique
• Process
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Copy chromosomes
Crossing over
Segregation
Segregation again
• Result
– 4 daughter cells
– ½ normal chromosomes
Meiosis
VIRUS
Virus occupy a twilight zone between the worlds of living
and nonliving things. Criteria commonly applied for living
things include (1) independent motility, (2) irritability (the
ability to respond to certain environmental stimuli), (3) the
ability to reproduce, and (4) the ability to specify the
genetic composition of progeny.
Viruses can have a wide variety of shapes and sizes.
This diagram of a bacterial virus shows the protein coat
containing DNA at the head. The tail fibers at the
bottom attach the virus to the cell wall. DNA is then
injected into the cell through the cylindrical core.
A diagram of the HIV virus. The reverse
transcriptase is the enzyme that initiates
reverse transcription in the virus.
THE AIDS VIRUS
Human immunodeficiency virus (HIV) was shown in 1984
to be the cause of the dreaded condition called immune
deficiency syndrome (AIDS).
In 2004
40 million people lived with it (1.1 million Americans)
5 million people acquired HIV
3.1 million people died of it
The central dogma of molecular biology
HIV is a human retrovirus, the third such virus to be
identified. Retroviruses (retro--from Latin means
"turning back" are named after the crucial step in their
growth cycle that involves the reversal of transcription,
the first half of the "central dogma of biology"
Organic Molecules
Four Basic Characteristics
• Most molecules based on chemistry of carbon
– Organic molecules
• Life’s molecules form from few elements
– H, O, C, N97.5% of body weight
• Molecules composed of simple building blocks
– Arranged differently
• Shape determines behavior
– Determines ability for bonding
Chemical Shorthand
• No H atoms or bonds to H are shown
• C atoms are not shown explicitly
Shorthand