Cells are

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Transcript Cells are

Cell Structure and Function
Cells
• Smallest living unit
• (plants and animals
are composed of
cells)
• Most are microscopic
Discovery of Cells
• Robert Hooke (mid-1600s)
– Observed sliver of cork
– Saw “row of empty boxes”
– Coined the term cell
Cell theory
• (1839)Theodor Schwann & Matthias Schleiden
“ all living things are made of cells”
• (50 yrs. Later) Louis Pasteur
“all cells come from cells”
Principles of Cell Theory
• All living things are made of cells
• The smallest living unit of structure
and function of all organisms is the
cell
• Cells carry out the functions needed
to support life.
• All cells arise from preexisting cells
(this principle discarded the idea of
spontaneous generation)
Why study cells?
• Cells  Tissues  Organs  Bodies
– bodies are made up of cells
– cells do all the work of life!
The Work of Life
• What jobs do cells have to do for an organism to live…
– “breathe”
• gas exchange: O2 in vs. CO2 out
– eat
• take in & digest food
– make energy
• ATP
ATP
– build molecules
• proteins, carbohydrates, fats, nucleic acids
– remove wastes
– control internal conditions
• homeostasis
– respond to external environment
– build more cells
• growth, repair, reproduction & development
• Cells provide structure and form to the
body.
• They appear in a variety of shapes;
round, concave,
rectangular, tapered,
spherical, and other.
• Cell shape seems to
be related to
specialized function.
Cell Size (Varies)
Cells are:
• Unit of Function: Each cell is a living unit.
A cell performs many metabolic functions
to sustain life. Each cell is a biochemical
factory using food molecules for energy;
repair of tissues, growth and ultimately
reproduction.
• Unit of Growth: Each living organism
begins as a single cell. Some organisms
such as a protist, remain unicellular. For a
multicellular organism, as the number of
cells increases in the body of a plant or
animal, so too does its size.
• Unit of heredity: New cells only arise from
preexisting cells. A cell grows to optimum
size and then divides, producing either two
cells identical to itself OR four cells not
identical.
• Cells carry hereditary information from one
generation to the next. This information is
coded in molecules of DNA
(deoxyribonucleic acid).
Characteristics of All Cells
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Have a surrounding membrane
Cytoplasm – cell contents in thick fluid
Organelles – structures for cell function
Control center with DNA
Cell Types
• Prokaryotic
• Eukaryotic
Two Types of Cells
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Prokaryotes
First cells to evolve
No nucleus
Hereditary info is
contained within
cytoplasm
• Ex. Bacteria
• Eukaryotes
• Evolved from
Prokaryotes
• Have a nucleus
• Hereditary Info is
contained within
the nucleus
• Ex. Plants,
Animals, Fungi
Prokaryotic Cells
• First cell type on earth
• Cell type of Bacteria and Archaea
Prokaryotic Cells
• No membrane bound nucleus
• Nucleoid = region of DNA concentration
• Organelles not bound by membranes
Bacterium Shapes
Eukaryotic Cells
• Nucleus bound by membrane
• Include fungi, protists, plant,
and animal cells
• Possess many organelles
Protozoan
Representative Animal Cell
Representative Plant Cell
Organelles
• Cellular machinery
Cell Walls
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•
•
•
•
Found in plants, fungi, & many protists
Surrounds plasma membrane
Made of cellulose
Is rigid
Provides support and
protection for the cell
Cell Wall Differences
• Plants – mostly cellulose
• Fungi – contain chitin
Cell membrane
• Surrounds all cells
• In a plant cell, it lies beneath the cell wall
• – In animal cells, it is the outer boundary (made of
cholesterol)
• Lipid bilayer with embedded proteins
• Provides cell with – Protection
• Isolates the cell’s contents from external environment
• Regulates the flow of materials into and out of the cell
(i.e. selectively permeable )
• Allows interaction among cells
• Support
Cytoplasm
• Viscous fluid containing organelles
• components of cytoplasm
– Interconnected filaments & fibers
– Fluid = cytosol
• Found in both plant and animal cells
• Located beneath cell membrane
• Supports and protects cell organelles
Organelles
• Functional components within cytoplasm
Nucleus
• Function
– control center of cell
– protects DNA
• instructions for building proteins
• Structure
– nuclear membrane
– nucleolus
• ribosome factory
– chromosomes
• DNA
DNA
• Hereditary material
• Chromosomes
Nucleic Acid
• Deoxyribonucleic acid (DNA) has two
functions:
• DNA controls protein synthesis in the cell
• DNA is replicated and passed on to
progeny cells during reproduction
Nucleolus
• Most cells have 2 or more
• Directs synthesis of RNA
• Forms ribosomes
Endoplasmic Reticulum
• Helps move substances within cells
• Network of interconnected tubes
• Two types
– Rough endoplasmic reticulum
– Smooth endoplasmic reticulum
Rough Endoplasmic Reticulum
• Ribosomes attached to surface
– Manufacture proteins
– Not all ribosomes attached to rough ER
Smooth Endoplasmic Reticulum
• No attached ribosomes
• Has enzymes that help build molecules
– Carbohydrates
– Lipids
Endo-membrane System
Golgi Apparatus
• Function
– finishes, sorts, labels & ships proteins
• like UPS headquarters
– shipping & receiving department
– ships proteins in vesicles
• “UPS trucks”
vesicles
carrying proteins
• Structure
– membrane sacs
transport vesicles
Lysosomes
• Found only in animal cells
• Contain digestive enzymes
• Functions
– Aid in cell renewal
– Break down old cell parts
– Digests invaders
Lysosome
Peroxisome
• Similar to lysosome
• Membrane-bound vesicle that contains
enzymes
• Enzymes are used to breakdown toxic
substances to hydrogen peroxide
• Hydrogen peroxide is broken down by
catalase to produce water and oxygen
Vacuoles
• Membrane bound storage sacs
• More common in plants than animals
• Contents
– Water
– Food
– wastes
Mitochondria
• Have their own DNA
• Bound by double membrane
• Has inner foldings (Cristae) that
increase the internal surface area
Mitochondria
• Break down fuel molecules (cellular respiration)
– Glucose
– Fatty acids
• Release energy
– ATP
• Function
Mitochondria
– make ATP energy from cellular respiration
• sugar + O2  ATP
• fuels the work of life
in both animal &
plant cells
ATP
•
Plants make energy two
ways!
ATP
Mitochondria
– make energy from sugar + O2
• cellular respiration
• sugar + O2  ATP
• Chloroplasts
– make energy + sugar from sunlight
• photosynthesis
• sunlight + CO2  ATP & sugar
– ATP = active energy
– sugar = stored energy
» build leaves & roots & fruit
out of the sugars
sugar
ATP
Chloroplasts
• Solar energy capturing organelle
Photosynthesis
• Takes place in the chloroplast
• Makes cellular food – glucose
Mitochondria are in both
cells!!
animal cells
plant cells
mitochondria
chloroplast
Cells need workers = proteins!
• Making proteins
– to run daily life & growth, the cell must…
• read genes (DNA)
• build proteins
– structural proteins (muscle fibers, hair, skin, claws)
– enzymes (speed up chemical reactions)
– signals (hormones) & receptors
– organelles that do this work…
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•
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nucleus
ribosomes
endoplasmic reticulum (ER)
Golgi apparatus
endoplasmic
reticulum
nucleus
protein
on its way!
DNA
RNA
vesicle
TO:
TO:
TO:
vesicle
ribosomes
TO:
finished
protein
protein
Golgi
apparatus
Making Proteins
Cells need to make more
cells!
• Making more cells
– to replace, repair & grow,
the cell must…
• copy their DNA
• make extra organelles
• divide the new DNA & new
organelles between 2 new
“daughter” cells
– organelles that do this work…
• nucleus
• centrioles
Centrioles
• Function
– help coordinate cell division
• only in animal cells
• Structure
– one pair in each cell
Cell Summary
• Cells have 3 main jobs
– make energy
• need food + O2
• cellular respiration & photosynthesis
• need to remove wastes
– make proteins
Our organelles
do all those
jobs!
• need instructions from DNA
• need to chain together amino acids & “finish”
& “ship” the protein
– make more cells
• need to copy DNA & divide it up to daughter cells
Plasma Membrane
• Contains cell contents
• Double layer of phospholipids & proteins
Phospholipids
• Polar
– Hydrophylic head
– Hydrophobic tail
• Interacts with water
Movement Across the Plasma Membrane
• A few molecules move freely
– Water, Carbon dioxide, Ammonia, Oxygen
• Carrier proteins transport some molecules
– Proteins embedded in lipid bilayer
– Fluid mosaic model – describes fluid nature of
a lipid bilayer with proteins
Molecule Movement & Cells
• Passive Transport
• Active Transport
• Endocytosis
(phagocytosis & pinocytosis)
• Exocytosis
Passive Transport
• No energy required
• Move due to gradient
– differences in concentration, pressure, charge
• Move to equalize gradient
– High moves toward low
Types of Passive Transport
1. Diffusion
2. Osmosis
3. Facilitated diffusion
Diffusion
• Molecules move to equalize concentration
Osmosis
• Special form of diffusion
• Fluid flows from lower solute concentration
• Often involves movement of water
– Into cell
– Out of cell
Solution Differences & Cells
• solvent + solute = solution
• Hypotonic
– Solutes in cell more than outside
– Outside solvent will flow into cell
• Isotonic
– Solutes equal inside & out of cell
• Hypertonic
– Solutes greater outside cell
– Fluid will flow out of cell
Facilitated Diffusion
• Differentially permeable membrane
• Channels (are specific) help molecule
or ions enter or leave the cell
• Channels usually are transport proteins
(aquaporins facilitate the movement of
water)
• No energy is used
Process of Facilitated Transport
• Protein binds with molecule
• Shape of protein changes
• Molecule moves across membrane
Active Transport
• Molecular movement
• Requires energy (against gradient)
• Example is sodium-potassium pump
Endocytosis
• Movement of large material
– Particles
– Organisms
– Large molecules
• Movement is into cells
• Types of endocytosis
– bulk-phase (nonspecific)
– receptor-mediated (specific)
Process of Endocytosis
• Plasma membrane surrounds material
• Edges of membrane meet
• Membranes fuse to form vesicle
Forms of Endocytosis
• Phagocytosis – cell eating
• Pinocytosis – cell drinking
Exocytosis
• Reverse of endocytosis
• Cell discharges material
Exocytosis
• Vesicle moves to cell surface
• Membrane of vesicle fuses
• Materials expelled
Membrane Proteins
1. Channels or transporters
– Move molecules in one direction
2. Receptors
– Recognize certain chemicals
Membrane Proteins
3. Glycoproteins
– Identify cell type
4. Enzymes
– Catalyze production of substances
Review of Eukaryotic Cells
Review of Eukaryotic Cells