    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

  Magnification=the ratio of an object’s image size to its real size Resolution=a measure of the clarity of the image

  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 Red Blood Cells Pollen grain

Ocular lens Objective lenses

2. Electron Microscope



Used to observe VERY small objects: viruses, DNA, parts of cells



Uses beams of electrons rather than light



Much more powerful

Above: Spider shown with a Scanning Electron Microscope     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

  

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

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

   Cells need to build proteins Cells need energy Cells need to make more cells

 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

   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!

Surface Area and Volume

  The surface area to volume ratio of a cell is critical. As the surface area increases by a factor of n 2 , the volume increases by a factor of n 3 Small cells have a greater surface area relative to volume Why is this important to cells? Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

10 m

The Size Range of Cells: http://learn.genetics.utah.edu/content/cells/

1 m 0.1 m

Most cells are between 1 and 100 micrometers in diameter (see light region of chart to the right .

1 cm 1 mm 100 µm 10 µm

Note: The scale is logarithmic, each reference mark is a tenfold increase in size from the bottom to top

1 µm 100 nm 10 nm 1 nm 0.1 nm Human height Length of some nerve and muscle cells Chicken egg Frog egg Most plant and animal cells Nucleus Most bacteria Mitochondrion Smallest bacteria Viruses Ribosomes Proteins Lipids Small molecules Atoms

   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

     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 A Typical Animal Cell:

ENDOPLASMIC RETICULUM ( ER) Rough ER Smooth ER Flagellum Centrosome Nuclear envelope Nucleolus Chromatin NUCLEUS Plasma membrane CYTOSKELETON: Microfilaments Intermediate filaments Microtubules Microvilli Peroxisome Mitochondrion Lysosome Golgi apparatus Ribosomes

Fig. 6-9b

NUCLEUS Nuclear envelope Nucleolus Chromatin Rough endoplasmic r eticulum

A Typical Plant Cell

Smooth endoplasmic reticulum Ribosomes Golgi apparatus Mitochondrion Peroxisome Plasma membrane Cell wall Wall of adjacent cell Central vacuole Microfilaments Intermediate filaments Microtubules CYTO SKELETON Plasmodesmata Chloroplast

 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



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

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)

  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 -)

 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 –  Thick layer  stains purple Polyalcohols called teichoic acids (negative charge)  Helps allow ions pass through   Gram Negative –  Thin layer   stains pink 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.

  Archaea – have walls containing specialized polysaccharides and proteins  NO peptidoglycan This absence is a reason they are classified as archaea and not bacteria

  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



Reproduction of Prokaryotic Cells

  All reproduce asexually Three main methods    Binary fission (most common) Snapping division Budding

Cell replicates its DNA.

Nucleoid The cytoplasmic membrane elongates, separating DNA molecules.

Cross wall forms; membrane invaginates.

Cross wall forms completely.

Daughter cells may separate.

Cell wall Cytoplasmic membrane Replicated DNA

MDufilho

Spores

DNA is replicated One daughter DNA molecule is moved into bud Young bud Daughter cell

    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.

  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.

    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 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)

 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.

      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

  “Endo”=inside Consists of: Nuclear Envelope, Endoplasmic Reticulum, Golgi Apparatus, Lysosomes, Vacuoles, and the Plasma Membrane

  “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 attached Rough ER=ribosomes attached

     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 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.

    “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”

   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

    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.

   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.

   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 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

   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.

  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

  Mitochondria and Chloroplasts change energy from one form to another. Mitochondria are the sites for cellular respiration; Chloroplasts are the sites for photosynthesis.

Mitochondrion Chloroplasts

   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.

  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 also have two membranes; the inner membranes form sacs that are stacked. In these membranes, chlorophyll (green pigment) traps sunlight energy.    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”

    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

   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.

   Organelles involved in organizing the cell so that it can divide are: Cytoskeleton Centrioles (in animal cells)

  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.

  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

ATP Vesicle Receptor for motor protein Motor protein ( ATP powered) Microtubule of cytoskeleton Microtubule Vesicles 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.

The cytoskeleton is composed of three main elements : 1.actin filaments (shown in

red

); also called microfilaments.

2.mictrotubules (

gold

) 3. intermediate filaments (

blue

) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

  Hollow tubes made of Tubulin Function: maintains cell shape, cell motility (as in cilia or flagella), chromosome movement in cell division, organelle movement.

Cilia Flagellum

  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)

  Made of fibrous proteins supercoiled into thicker cables Function: maintenance of cell shape, anchoring nucleus and certain organelles

  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 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.

   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.

  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 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.

 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