all organisms are made of cells the cell is the simplest collection of matter that can live cell...
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CELLS
Overview: The Fundamental Units of Life
All organisms are made of cells The cell is the simplest collection of matter
that can live Cell structure is correlated to cellular
function Cells come from other cells
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
To Study Cells, Biologists use Microscopes
Magnification=the ratio of an object’s image size to its real size
Resolution=a measure of the clarity of the image
1. Compound/Light Microscope
cannot resolve detail finer than 200 nm, the size of a small bacterium—that’s about 1,000 times the size of the object.
Advantage: Light Microscopes can observe living organisms
Pollen grain
Red Blood Cells
Ocular lens
Objective lenses
Types of Microscopes
2. Electron MicroscopeUsed to observe VERY small objects: viruses, DNA, parts of cells
Uses beams of electrons rather than light
Much more powerful
Electron Microscopes
Electron Microscopes were first invented in the 1950s.
They focus a beam of electrons through a specimen or onto its surface.
They have a resolution 100 X better than a light microscope.
Disadvantage: Only nonliving material can be studied
Above: Spider shown with a Scanning Electron Microscope
Types of Microscopes
3. Transmission Electron Microscope (TEM) electrons pass through thin sections of a
specimen denser regions in specimen, scatter more
electrons and appear darker Can magnify up to 250,000x
Types of Microscopes
4. Scanning Electron Microscope (SEM) uses electrons to create image produces a 3-dimensional image of
specimen’s surface features Can magnify up to 100,000x
What Do Cells Need to Do Every Day?
Cells need to build proteins Cells need energy Cells need to make more cells
Cells Need to Make Proteins
Proteins are macromolecules that are used by organisms for many different things: Building cell structures Transporting nutrients such as oxygen Enzymes speed up chemical reactions Hormones regulate functions of systems Defensive proteins guard against infection Responsive proteins communicate with other
cells
Cell Sizes
Size is a general aspect of cell structure that relates to function
Limits to cell size are due to the logistics of carrying out cell functions
Having organelles to move materials around allows eukaryotic cells to be larger than prokaryotic cells.
Elephants don’t have larger cells than other organisms—they just have more cells!
The surface area to volume ratio of a cell is critical. As the surface area increases by a factor of n2, the volume increases by a factor of n3
Small cells have a greater surface area relative to volume
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Surface Area and Volume
Why is this important to cells?
10 m
1 m
0.1 m
1 cm
1 mm
100 µm
10 µm
1 µm
100 nm
10 nm
1 nm
0.1 nm Atoms
Small molecules
Lipids
Proteins
Ribosomes
Viruses
Smallest bacteria
Mitochondrion
Nucleus
Most bacteria
Most plant and animal cells
Frog egg
Chicken egg
Length of some nerve and muscle cells
Human height
Un
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eye
Lig
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mic
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Ele
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mic
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The Size Range of Cells:
Most cells are between 1 and 100 micrometers in diameter (see light region of chart to the right .
Note:The scale is logarithmic, each reference mark is a tenfold increase in size from the bottom to top
http://learn.genetics.utah.edu/content/cells/
Comparing Cells
All cells have a plasma/cell membrane surrounding the cytosol (a semifluid, jellylike substance in which organelles are found)
All cells contain chromosomes and ribosomes
Variations in other components can be found between cells
Viruses
Eukaryotic Cells
have DNA enclosed by a membrane in the nucleus.
“Eu”= True In addition, they have
other membrane-bound organelles in the cytoplasm
Generally, much larger than prokaryotic cells
All organisms except bacteria have eukaryotic cells
Fig. 6-9a
ENDOPLASMIC RETICULUM (ER)
Smooth ER
Rough ERFlagellu
m
Centrosome
CYTOSKELETON:
MicrofilamentsIntermediate
filamentsMicrotubules
Microvilli
Peroxisome
Mitochondrion Lysosom
e
Golgiapparatus
Ribosomes
Plasma membrane
Nuclearenvelope
NucleolusChromatin
NUCLEUS
A Typical Animal Cell:
Fig. 6-9b
NUCLEUS
Nuclear envelopeNucleolusChromatin
Rough endoplasmic reticulum
Smooth endoplasmic reticulumRibosomes
Central vacuole
MicrofilamentsIntermediate filaments
Microtubules
CYTO-SKELETON
Chloroplast
PlasmodesmataWall of adjacent
cell
Cell wall
Plasma membrane
Peroxisome
Mitochondrion
Golgiapparatus
A Typical Plant Cell
Prokaryotic Cells
Prokaryotic cells are characterized by having No nucleus DNA in an unbound
region called the nucleoid
No membrane-bound organelles
“Pro”=before “karyo”=kernel/nucleus Bacteria are
Prokaryotic
General Characteristics of Prokaryotic Organisms
Prokaryotes Most diverse group of cellular microbes Habitats
From Antarctic glaciers to thermal hot springs From colons of animals to cytoplasm of other
prokaryotes From distilled water to supersaturated brine From disinfectant solutions to basalt rocks
Only a few capable of colonizing humans and causing disease
Prokaryotes
External Structures Glycocalyces – gelatinous, sticky
substance that surrounds outside of cell Polysaccharides, polypeptide Form capsule or slime layer (loose, water
soluble) that protects cells from drying Cause disease
Slime on teeth Similar to substances found in the body (cause
pneumonia)
Prokaryotic Cell Walls
Most composed of peptidoglycan (complex polysaccharide)
From the peptidoglycan inwards all bacteria are very similar the bacterial world divides into two major
classes (Gram + and Gram -)
Peptidoglycan huge polymer of interlocking chains of alternating monomers
Provides rigid support while permeable to solutes
Backbone of peptidoglycan molecule composed of two amino sugar derivatives of glucose. The “glycan” part of peptidoglycan:
- N-acetylglucosamine (NAG) - N-acetlymuramic acid (NAM)
NAG / NAM strands are connected by interlocking peptide bridges. The “peptid” part of peptidoglycan.
Gram positive – stains purple Thick layer Polyalcohols called teichoic acids (negative
charge) Helps allow ions pass through
Gram Negative – stains pink Thin layer Outer layer – composed of lipopolysachharide
(LPS) Proteins called porins form channels
Dead cell releases Lipid A Trigger fever, vasodilation, inflammation,
shock, blood clotting Outer membrane may inhibit penicillin
Why are these differences important?
Gram-negative bacteria: fewer interpeptide bridges but have an outer membrane made of lipopolysaccharides (LPS), part of that molecule, Lipid-A, is a toxin.
Penicillins and cephalosporins interfere with linking of interpeptides, but can’t easily get to in gram - bacteria
Cell walls without enough of these intact cross-links are structurally weak, and disintegrate when cells divide.
Since the eukaryotic cells of humans do not have cell walls, our cells are not damaged by these drugs.
Microorganisms that do not contain peptidoglycan are not susceptible to these drugs.
Bacteria without cell walls
Archaea – have walls containing specialized polysaccharides and proteins NO peptidoglycan
This absence is a reason they are classified as archaea and not bacteria
Cytoplasm of Prokaryotes
Inclusions Reserves of nutrients Store as glycogen or lipid polymer poly –β-
hydroxybutric acid (PHB) Used as a plastic that are biodegradable
Endospores Peptidoglycan and spore coat form around
DNA and some cytoplasm Defensive strategy against hostile or
unfavorable conditions
General Characteristics of Prokaryotic Organisms
Reproduction of Prokaryotic Cells All reproduce asexually Three main methods
Binary fission (most common) Snapping division Budding
FIGURE 11.2 BINARY FISSIONCell replicates its DNA.
Nucleoid
Cell wallCytoplasmicmembraneReplicatedDNA
The cytoplasmicmembrane elongates,separating DNAmolecules.
Cross wall forms;membraneinvaginates.
Cross wall formscompletely.
Daughter cellsmay separate.
FIGURE 11.3 SNAPPING DIVISION-OVERVIEW
MDufilho
FIGURE 11.4 ACTINOMYCETES SPORES
Spores
FIGURE 11.5 BUDDING
DNA is replicated
One daughter DNAmolecule is movedinto bud
Young bud
Daughter cell
The Nucleus: Information Central
The nucleus contains most of the genes in the eukaryotic cell
It is generally the most conspicuous organelle in a eukaryotic cell
The Nuclear Envelope encloses the nucleus
Chromatin contains the DNA of the cell—it is organized into individual chromosomes.
The nuclear envelope is a double membrane. It is perforated with pore structures. An intricate protein structure called a pore complex surrounds each pore.
How does the Nucleus Control the Cell’s Activities?
The Nucleus is like the “brain” of the cell—controlling most of the activities of the cell. How does it do this? By controlling what proteins are made.
Proteins are the workhorse molecules of the cell—they are made by ribosomes.
To Control the Production of Proteins:
The nucleus contains the following organelles that are needed for protein synthesis:
Nucleolus—builds rRNA and Ribosomes
Chromosomes/Chromatin—contains strands of DNA
Nuclear Membrane—has pores to allow mRNA to leave nucleus and go to ribosomes
Ribosomes
Ribosomes are particles made of ribosomal RNA and protein
Ribosomes carry out protein synthesis in two locations: In the cytosol (free
ribosomes) On the outside of the
endoplasmic reticulum or the nuclear envelope (bound ribosomes)
The Central Dogma of Molecular Biology
DNA Controls the production of proteins in a series of steps that begins in the nucleus and ends at ribosomes.
Remember: Proteins do the work of the cell.
DNA directs which proteins are made.
Ribosomes build the proteins.
Cells Need Energy
Take in nutrients Take in oxygen Build cell structures Remove wastes Make ATP Cells use many
organelles to obtain, store, and release energy: plasma membrane, ER, Golgi Apparatus, Lysosomes, Mitochondria and Chloroplasts
ATP
The Endomembrane System
“Endo”=inside Consists of: Nuclear Envelope,
Endoplasmic Reticulum, Golgi Apparatus, Lysosomes, Vacuoles, and the Plasma Membrane
Endoplasmic Reticulum
“Endo”=inside; “plasm”=liquid; “reticula”=intricate network
ER is an intricate network of membranes that start at the nuclear membrane and continue throughout the cell to the plasma membrane.
Smooth ER=no ribosomes attachedRough ER=ribosomes attached
Smooth vs. Rough ER
Smooth ER: Makes lipids Metabolizes
carbohydrates Detoxifies poisons Stores calcium
Rough ER: Because ribosomes
are attached, many proteins are made here, especially glyco-proteins. (what are these?)
Distributes proteins in vesicles (little membrane-bound bundles of proteins)
Makes membranes for the cell
Golgi Apparatus
Golgi Apparatus is a complex of flattened sacs of membranes (called cisternae).
Function: Modifies products of
the ER Manufactures certain
macromolecules Sorts and packages
materials into transport vesicles
The Golgi is like the UPS store: It is the packaging and shipping center of the cell.
Lysosomes
“lysis”=to split Lysosomes are sacs
of enzymes that can digest large molecules
These enzymes can digest proteins, fats, polysaccharides, and nucleic acids—basically anything that enters the cell!
They can even digest organelles in the cell
Lysosomes may be called the “Stomach” of the cell; or even “The Suicide Sac”
How Do Lysosomes Work?
Some types of cell can engulf another cell by phagocytosis; this forms a food vacuole
A lysosome fuses with the food vacuole and digests the molecules
Autophagy: The lysosome can also digest damaged organelles
Lysosomal Enzymes
These enzymes work best at pH 5
The lysosome makes its own enzymes
The pH inside the lysosome stays at ph 5 because the transport proteins in the membrane pump in H+ ions.
These enzymes don’t work well in the pH of the rest of the cell. Why? (so it won’t digest the cell if it leaks)
White Blood Cells such as this one contain many lysosomes. They engulf bacteria and digest them.
When Things Go Bad…
Lysosome diseases are often fatal.
The enzymes in the lysosome may be defective…if so, when the lysosome takes in macromolecules, they may not get digested properly
Undigested material builds up and lysosome gets larger & larger, eventually disrupting cells and organs.
Tay-Sachs disease is a genetic disease that causes fat molecules to build up in the brain. Affected children usually die before age 3.
But sometimes, cells need to die….
Lysosomes can be used to kill cells when they are supposed to be destroyed
Some cells have to die for proper development in an organism
Apoptosis= “auto-destruct” process; lysosomes break open & kill the cell. Why?
Tadpoles lose their tails as they mature
Fingers are fused in the human embryo
Vacuoles—Storage Organelles
Vacuoles are membrane-bound organelles whose functions vary—but most are used for storage of needed materials
Food vacuoles: formed by phagocytosis, then store food to be broken down by lysosomes
Central Vacuoles of Plants The central vacuole of
mature plant cells develops from smaller vacuoles that come from the ER and Golgi apparatus.
This organelle in plants stores proteins, sugars, ions and water. Some may contain pigments to give color to flowers.
They may contain poisonous substances that keep the plant from being eaten.
The membrane around the central vacuoles is called the tonoplast.
Contractile Vacuoles of Protists
Protists are fresh-water single-celled organisms. They live in an environment that causes water to constantly diffuse into their body. This could cause swelling and death.
Contractile Vacuoles act like water pumps, continually pumping water out of the cell. Contractile Vacuoles in a
Paramecium
Cells Need Energy—How do they get it?
Mitochondria and Chloroplasts change energy from one form to another.
Mitochondria are the sites for cellular respiration; Chloroplasts are the sites for photosynthesis.
MitochondrionChloroplasts
Mitochondria
Mitochondria –where cellular respiration occurs.
Where the chemical energy stored in sugars such as glucose is converted to ATP—a molecule that stores cellular energy.
The “Powerhouse” of the cell
Mitochondria have 2 membranes; the inner one is folded to increase the surface area. Enzymes attached to the membranes do the work of the mitochondria.
Mitochondria
Almost all eukaryotic cells have mitochondria—either one very large mitochondrion, or thousands of smaller ones.
Which types of cells would have lots of mitochondria? Hint: Which cells need a lot of energy?
Chloroplasts
Chloroplasts, found in plants and algae are where photosynthesis occurs
They convert the energy from sunlight into organic compounds such as glucose.
“Little Green Sugar Factories”
Chloroplasts also have two membranes; the inner membranes form sacs that are stacked. In these membranes, chlorophyll (green pigment) traps sunlight energy.
Mitochondria and Chloroplasts—It’s Important to See Similarities Both transform
energy from one kind to another
Both make ATP Both have double
membranes Both are semi-
autonomous organelles—they can move, change shape, and divide
Both have their own DNA and ribosomes—almost like independent cells-within-a-cell
Peroxisomes
A peroxisome is a specialized metabolic compartment.
Peroxisomes contain special enzymes that remove hydrogen from various substrates to form H2O2 (hydrogen peroxide).
This process may detoxify poisons, or break down fuel for energy.
Peroxisomes produce H2O2 as a by-product of many of the reactions in a cell.
H2O2 is toxic, so the peroxisome has an enzyme, catalase, that breaks down H2O2.
Cells Need to Make More Cells
Organelles involved in organizing the cell so that it can divide are:
Cytoskeleton Centrioles (in
animal cells)
Cytoskeleton
The cytoskeleton is a network of fibers that organizes structures and activities in the cell.
It gives the cell shape and support, much like the framework of a building holds it up and divides it into rooms.
Cytoskeleton Functions
Besides giving shape to the cell, the cytoskeleton anchors the other organelles.
It can be quickly dismantled in one part of the cell, then reassembled in a new location, changing the shape of the cell!
The cytoskeleton consists of three types of structures:Microtubules, Microfilaments, and Intermediate filaments
VesicleATP Receptor for
motor protein
Microtubuleof cytoskeleton
Motor protein (ATP powered)
MicrotubuleVesicles 0.25 µm
By interacting with motor proteins, the cytoskeleton can move whole cells or just move parts of the cell around. Inside the cell, vesicles can travel to their destinations along “monorails” provided by the cytoskeleton.
Components of the Cytoskeleton
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
The cytoskeleton is composed of three main elements : 1.actin filaments (shown in red); also called microfilaments.2.mictrotubules (gold) 3. intermediate filaments (blue)
Microtubules
Hollow tubes made of Tubulin Function: maintains cell shape, cell
motility (as in cilia or flagella), chromosome movement in cell division, organelle movement.
CiliaFlagellum
Microfilaments
Tiny thread-like fibers made of 2 intertwined strands of actin
Function: Maintains cell shape, changes in cell shape, muscle contraction, cytoplasmic streaming, cell motility (as in pseudopodia), and cell division (cleavage furrow formation)
Intermediate Filaments
Made of fibrous proteins supercoiled into thicker cables
Function: maintenance of cell shape, anchoring nucleus and certain organelles
Centrosomes & Centrioles
In animal cells, microtubules grow out from a centrosome which is located near the nucleus.
Within the centrosome is a pair of centrioles, each made of 9 sets of triplet microtubules. Centrioles in
animal cells are essential for cell division.
They are not found in plant cells.
Cilia and Flagella
Cilia are hairlike extensions of certain cells that enable the cell to move or move fluid across the surface of the cell.
Flagellum are singular long, tail-like extensions that also enable certaincells to move.
Both cilia and flagella are made of microtubules.
Plant Cell Walls
The cell wall is found outside the plant cell.
Cell walls protect the plant cell, maintains its shape, and prevents excessive uptake of water.
Cell walls are made mostly of microfibrils of cellulose.
Plant Cell Walls
A young plant first secretes a relatively thin and flexible cell wall called the primary cell wall.
Between primary cell walls of adjacent cells is the middle lamela, a thin layer rich in sticky polysaccharides called pectin.
Some cells will add a secondary cell wall outside the primary cell wall. Wood is primarily secondary cell walls
Plant Cell Walls are held together with Pectin
Plant cellulose cell walls from the ragweed plant anther (Ambrosia psilostachya).
The rigid cell wall of plants is made of fibrils of cellulose embedded in a matrix of several other kinds of polymers such as pectin and lignin.
Although each cell appears encased within a box, in fact primary cell walls are perforated permitting plasmodesmata to connect adjacent cells.
The Extracellular Matrix
Animal cells do not have cell walls, but they do have an elaborate extracellular matrix. The main ingredients are glycoproteins (the most abundant is collagen). Proteoglycans are
proteins with many carbohydrate chains attached.Integrins are proteins embedded in the cell membrane that attach to the extracellular matrix.The main functions of the ECM: adhesion, support, regulation