Structure and Function of Cells

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• Structure and Function of Cells

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Structure and Function of Cells

• OBJECTIVES
• Define the cell doctrine
• Relate cell structure to function
• List and describe a cells internal
  structure/function of organelles
• Describe plasma membrane
• Discuss how to transport material across the
  membrane
• Explain how cells use and transform matter and
  energy

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Cell Doctrine

• All living things are composed of cells
• A single cell is the smallest unit that exhibits
  all of the characteristics of life
• All cells come only from preexisting cells

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Cells Are Classified According to Their Internal
Organization

• Prokaryotic Cells
• Plasma membrane
• No nucleus
• Cytoplasm fluid within membrane
• No true organelles

• Eukaryotic Cells
• Plasma membrane
• Nucleus membrane bound information center
• Cytoplasm fluid within membrane
• Organelles membrane bound structures with
  specialized functions
• All human cells are eukaryotic

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Figure 3.1
Plasma membrane
Cell wall
Cytoplasm
Organelles
Nucleus
A eukaryotic animal cell has a nucleus and
numerous small organelles. The cytoplasm is
enclosed by a flexible plasma membrane.
Prokaryotic cells such as this bacterium have a
rigid cell wall surrounding the plasma membrane.
The genetic material is not surrounded by a
membrane, and there are no organelles in the
cell. The elongated bacterium in the center of
the photo is about to divide in two, as its
genetic material is concentrated at both ends of
the cell.
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Figure 3.2
A portion of several muscle cells of the heart
Nerve cells of the central nervous system carry
signals over distances
Cell Structure Reflects Cell Function
Red blood cells
Cells lining a tubule of a kidney
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Figure 3.3

• Small cells have a higher surface to volume ratio
• High surface to volume ratio promotes efficiency
  in
• Acquisition of nutrients
• Disposal of wastes

Eight small cells.
Cell with microvilli on one surface.
One large cell.
Cells Remain Small to Stay Efficient
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Plasma Membrane

• A semi-permeable lipid bilayer
• Phospholipids has polar head and nonpolar tail
• Cholesterol increases membrane strength
• Proteins various function (e.g. transport,
  receptor)
• Carbohydrates recognition
• Plasma membrabe is very important in cell
  homeostasis!!!

Hydrophilic
one layer of lipids
Hydrophobic
one layer of lipids
Hydrophilic
http//www.youtube.com/watch?vQqsf_UJcfBc
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Figure 3.5
Extracellular environment
Carbohydrate groups
Channel protein (always open)
Receptor protein
Gated channel Protein (closed position)
Lipid bilayer
Glycoprotein
Phospholipid
Transport protein
Cytoskeleton filaments
Cytoplasm
Cholesterol
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Molecules Cross the Plasma Membrane in Several
Ways

• Passive transportdoes not need energy
• Diffusion
• Osmosis
• Active transportmust use energy
• Transport in bulk
• Involves membranous vesicles to move larger
  substances
• Endocytosis
• Exocytosis

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Passive Transport Principles of Diffusion and
Osmosis

• Passive transport transports a substance without
  using energy
• Diffusion movement of molecules from
• High concentration ? Low concentration
• Down the gradient
• Osmosis the diffusion of water across a
  selectively permeable membrane
• Water moves from an area of low solute
  concentration to an area of high solute
  concentration

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Figure 3.8
Higher concentration
Lower concentration
Diffusion through the lipid layer. Lipid-soluble
molecules such as O2 and CO2 diffuse freely
through the plasma membrane.
Diffusion through channels. Some polar and
charged molecules diffuse through protein
Channels. Water is a typical example.
Facilitated transport. Certain molecules bind to
a protein, triggering a change in protein shape
that transports the molecule across the
membrane. Glucose typically enters cells by
this method.
https//www.youtube.com/watch?vprfMUwjobo8
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Active Transport Requires Energy

• Active transport moves substances from an area of
  lower concentration to an area of higher
  concentration
• Transported substance moves against the
  concentration gradient
• Requires ATP as energy
• Example sodium-potassium pump
• expels 3 Na ions
• imports 2 K ions
• uses ATP
• http//highered.mcgraw-hill.com/sites/0072495855/s
  tudent_view0/chapter2/animation__how_the_sodium_po
  tassium_pump_works.html

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Endocytosis and Exocytosis Move Materials in Bulk

• Used to move larger molecules
• Endocytosis brings substances into the cell
• As substance enters, it is surrounded by a
  membrane forming a membrane-bound vesicle
• Exocytosis expels substances from the cell
• Substance is contained within a membranous
  vesicle, which then fuses with the membrane,
  releasing the substance to the external
  environment

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Figure 3.10
Extracellular environment
Plasma membrane
Cytoplasm
Vesicle
Endocytosis. In endocytosis, material is
surrounded by the cell membrane and brought into
the cell.
Exocytosis. In exocytosis, a membranous vesicle
fuses with the plasma membrane, expelling its
contents outside the cell.
Photomicrograph showing various stages
of endocytosis.
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Tonicity Affects Cell Volume

• Tonicity comparison of the concentration of
  solutes in two different fluids or environments
• Q What happens to the cell in each case?

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Figure 3.14
Cytosol Semifluid gel material inside the cell
Nucleus Information center for the cell. Contains
DNA
Peroxisome Destroys cellular toxic waste
Centrioles Microtubular structures involved in
cell division
Cytoskeleton Structural framework of the cell
Smooth endoplasmic reticulum Primary site of
macro- molecule synthesis other than proteins
Rough endoplasmic reticulum Primary site of
protein synthesis by ribosomes
Golgi apparatus Refines, packages, and ships
macromolecular products
Secretory vesicle Membrane-bound shipping
container
Mitochondrion Produces energy for the cell
Ribosomes Site of protein synthesis
Plasma membrane Controls movement of materials
into and out of cell
Lysosome Digests damaged organelles and cellular
debris
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The Nucleus Controls the Cell

• Function
• Contains the genetic information of the cell
• Controls all of the activities of the cell
• Structural features
• Double-layered nuclear membrane
• Nuclear pores
• Chromosomes/chromatin
• Nucleolus

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Endoplasmic Reticulum (ER)

• Highly folded membranous network
• Two types of endoplasmic reticulum (ER)
• Rough ER
• Has ribosomes on surface- Protein manufacturing
• Smooth ER
• No ribosomes on surface- Lipid synthesis,
  including the synthesis of some hormones

Rough ER
Smooth ER
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• Ribosomes- site of protein synthesis
• Free floating in cytoplasm
• These ribosomes synthesize proteins for use in
  the cell
• Bound attached to endoplasmic reticulum
• These ribosomes synthesize proteins that will be
  exported from the cell

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Golgi Apparatus Refines, Packages, and Ships

• Protiens are modified packaged into vesicles
  and shipped to other locations

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Vesicles

• Peroxisomes
• Contain enzymes that detoxify wastes produced by
  the cell
• Lysosomes
• Contain digestive enzymes

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Mitochondria Provide Energy

• Power plant of the cell
• Surrounded by a double membrane
• Site of cellular respiration
• Utilizes O2
• Generates ATP

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Fat and Glycogen Sources of Energy

• Fat cells store
• Triglycerides
• Long-term energy storage
• Muscle and liver cells store glycogen
• Carbohydrate storage
• Short-term energy storage in animals

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Structures for support and movement

• Cytoskeleton
• Microtubules tiny hollow tubes of protein
• Microfilaments thin solid fibers of protein
• Microtubules and microfilaments form framework
  that supports the cell
• Centrioles
• Short rod-like structures near nucleus
• Play important role in cell division

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Structures for support and movement

• Cilia
• Short, many
• Found on cells lining airways
• Flagella
• Long, single
• Enable spermatozoa to swim
• Cilia and flagella have similar internal structure

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Cells Use and Transform Matter and Energy

• Metabolism sum of all chemical reactions in an
  organism
• Two types of metabolic pathways
• Anabolism
• Assembly of larger molecules from smaller ones
• Requires energy (ATP input)
• Catabolism
• Larger molecules are broken down
• Releases energy (ATP output)

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Glucose Provides the Cell with Energy

• Metabolic activities of a living cell require a
  lot of energy
• Energy in glucose is used to generate ATP
• One glucose molecule may yield 36 ATP
• In absence of glucose, fats, and protein can be
  catabolized to generate ATP

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Glucose Provides the Cell with Energy

• Cellular respiration the breakdown of glucose in
  the presence of oxygen to yield ATP
• Four stages of cellular respiration
• Glycolysis
• Preparatory step
• Citric acid cycle
• Electron transport system

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Cellular respiration

• Cellular respiration major catabolic pathway
  that provides energy (C6H12O6 6O2 ? 6H2O 6CO2
  energy)
• Glycolysis glucose (C6H12O6) split into two
  pyruvates
• Pyruvate converted to 2acetyl-Co A ( CO2
  released)
• Citric acid (Krebs) cycle acetyl-CoA broken into
  CO2
• H ions and electrons from glucose used in
  electron transport system to provide energy to
  make ATP

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Figure 3.29a
2 NADH
?2 ATP
to shuttle electrons from NADH in
cytosol to NADH within mitochondrion
Mitochondrion
2 FADH2
6 NADH
2 NADH
Electron transport chain and oxidative phosphoryla
tion
Glycolysis
Citric acid cycle
2 Acetyl CoA
Preparatory step
2 Pyruvate
Glucose
? 2 ATP
? about 34 ATP
?2 ATP
? 4 ATP
to initiate glycolysis
by oxidative phosphorylation
by substrate-level phosphorylation
About 36 ATP
Most of the ATP generated during cellular
respiration is synthesized in the electron
transport system.
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Fats and Proteins Are Additional Energy Sources

• Glycogen (storage form of glucose)
• Can be rapidly catabolized to glucose which then
  participates in cellular respiration
• 1 of total energy reserves
• Fats 78 of total energy reserves
• Triglycerides have twice the energy of
  carbohydrates
• Proteins 21 of total energy reserves
• Have the same amount of energy as carbohydrates

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Some Questions

• Compare and contrast prokaryotic and eukaryotic
  cells
• Why is the rough endoplasmic reticulum rough?
• What are lysosomes? Give their function.
• Which organelle converts the energy stored in
  food to ATP?
• Which cell part is important for transporting
  material maintaining homeostasis within the
  cell?
• What cells/tissue are most likely to store
  glycogen?
• What cells/tissue store triglycerides?
• What term describes the combination of all
  catabolic and anabolic reactions?