Download Biology 1: Chap. 3 – Cell Structure Looking at Cells Objectives

Biology 1: Chap. 3 – Cell Structure
I. Looking at Cells
A. Objectives
1. Describe how scientists measure the length of objects
2. Relate magnification and resolution in the use of microscope
3. Analyze how light microscopes function
4. Compare light microscopes with electron microscopes
5. Describe the scanning tunneling microscope
B. Types of Microscopes
1. Compound Light: Light passes through 1 or more lenses to enlarge image
a. Uses a light to illuminate specimen
b. Total magnification= objective X eyepiece
c. Can magnify up to 2000x
d. Specimen can be alive or dead
2. Electron Microscopes – form an image using a beam of e- (not light); specimen must be in
vacuum (air would interfere with e- beam)
a. Can magnify up to 200,000x
b. Transmission e- microscope (TEM) - beam of e- pass through a thin sample stained with ions
i. Some parts absorb e- while other parts allow e- to pass through
ii. E- that pass through strike sensor and creates a black and white image
iii. This type of microscope is used to see the inside of cells
c. Scanning e- microscopes (SEM) - beam of e- travel over surface of specimen that has been
coated with a thin layer of metal
i. E- bounce off of specimen and create 3-d image
d. Scanning Tunneling Microscope – (aka scanning probe)
i. Needle like probe measures difference in voltage caused by e- that leak (or tunnel) from
the surface of the object being viewed
ii. Can see down to the atomic level — 10,000,000 x
iii. Computer helps create a 3-D image
iv. Can be used for living or non-living specimen
C. Properties of Microscopes
1. Pictures/Images are called micrographs
2. Magnification – making an image look bigger
3. Resolution – measure of the clarity of the image
a. Being able to distinguish 2 objects that are close together as 2 separate objects
b. Electron microscopes have better magnification and resolution than light microscopes
D. Parts of the Microscope
1. Objective – silver tube with different lenses
a. High – longest (40 X)
b. Medium (10 X)
c. Low – shortest (4 X)
2. Revolving nosepiece (Objective mount) – the piece that holds the objectives and allows them to
rotate; found at end of body tube
3. Eyepiece / ocular - what you look through
4. Body Tube – connects eyepiece & objective – holds the prism for bending image
5. Coarse adjustment – larger knob, moves body tube up & down, or moves the stage up and
down- adjusts the working distance between the bottom of the lens and the top of the
slide/stage
6.
Fine adjustment – the smaller knob – gets the details sharp – each person will have a different
level of fine focus
7. Stage – has an opening in it to allow light through– holds the slide
8. Stage Clips – holds the slide in place over the stage opening
9. Iris Diaphragm - a disc or lever under the stage that controls the amount of light coming up
through the stage
10. Light Source – light bulb
11. Field of View – the lighted circular area you see when you look through the eyepiece – the area
that you can see.
II. Cell Features
A. Objectives
1. List the parts of the cell theory
2. Determine why cells must be relatively small
3. Compare the structure of prokaryotic cells with that of eukaryotic cells
4. Describe the structure of cell membranes
B. Cell Theory
1. All living things are made of one or more cells
2. Cells are the basic units of structure and function in living things
3. All cells arise from existing cells
C. Important scientists:
1. Robert Hooke (1665) – coined term “cell,” to describe what he saw when looking at slices of
dead cork
2. Anton Van Leeuwenhoek (1675) – Dutch scientist; looked at pond water and called them
“animalcules,” things we now call protists
3. Schleiden (1838) – German botanist – said cells make up not only stems and roots but every
part of the plant
4. Schwann (1839) – German zoologist - said animals are made of cells
5. Rudolph Virchow (1858) – German physician – said cells come from other cells
D. Cell Size
1. Small cells are more efficient than large ones
a. All substances that enter/exit a cell must cross over the cell membrane
b. When a cell grows, the volume grows much faster than the surface area (area of
membrane)
c. Result: when cells get too large there are traffic jams with materials trying to get into/out of
the cells
E. Types of Cells
1. Prokaryotes – smallest, simplest, no true nucleus
a. Bacteria are the only living prokaryotes
b. DNA found in loops not bound to nucleus
c. Have a cell wall outside cell membrane
d. Some have a polysaccharide mucus like covering outside the cell wall called a capsule—this
lets them cling to surfaces
e. Some do not need oxygen
f. Some have a long tail called flagella for movement
2. Eukaryotes – cells with a true nucleus that keeps DNA separate from rest of cell
a. Have other organelles - structures that carry out specific functions in the cell
F. Organelles
1. Nucleus – Control Center
a. Holds the DNA (hereditary info)
2.
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i. Chromatin – clumpy/grainy, formless mass of DNA; during cell “rest” (not dividing)
ii. Chromosome – strands or stringy form of DNA; during cell division
b. Protected/kept separate from the rest of the cell by nuclear membrane/nuclear envelope
i. 2 layers thick ( 2 layers of fat/lipids)
ii. Has pores or channels for movement of RNA, proteins, ribosomes, etc., into and out of
nucleus
c. Nucleolus– round structure inside the nucleus that manufactures the ribosomes
Cytoplasm– aka cytosol
a. Made mostly of water (70%)
b. Gel like substance where rxns take place
c. Helps to hold other organelles in place
Cytoskeleton– network of protein fibers & filaments that anchor the other organelles in the
cytoplasm– keeps membrane from collapsing
3 types of cytoskeleton fibers
a. Long slender microfilaments made of a protein called actin
i. Connect to proteins in cell membrane
ii. Can contract to change the shape of the cell like tiny muscle fibers
b. Microtubules– long hollow protein tubes made of protein called tubulin
i. Highway system for transportation of info from nucleus to other parts of the cell
ii. “train tracks” guide movement of RNA during protein synthesis & chromosomes during
cell division
c. Thick ropes of protein called Intermediate fibers
i. Act like fences
ii. Helps keep ribosomes and enzymes in certain areas, so enzymes can be kept nearby for
metabolic rxns
Cell Membrane – aka plasma membrane
a. Holds cell contents but not rigid, it is flexible
b. Made up of lipids which makes it tough
c. Selectively permeable or semi-permeable – due to lipid structure and pores, certain things
can’t go into/out of cells
i. Main function is to regulate what enters and leaves the cell
ii. General rule – the membrane will allow small, non-charged, nonpolar molecules to pass
d. Made of 2 layers of phospholipids (lipid bilayer) with protein embedded
e. Phospholipid – lipids made of a phosphate (polar “head”) with 2 fatty acids (nonpolar “tail”)
f. Membrane proteins – some are polar, some are non-polar so they interact with the
phospholipids to stay in place or move around as needed
i. Marker proteins – advertise what type of cell it is (liver, heart, etc)
ii. Receptor proteins – bind to specific substrates outside the cell to let them in/out of cell
1. Lets cells receive messages from other cells to coordinate activity
2. Acts like a security guard
iii. Enzymes – they are embedded in the cell membrane for biochemical reactions inside
cell
iv. Transport proteins – Help move substances into/out of cell
1. Act like revolving doors or tunnels
2. Help movement of ions or polar molecules across membrane
3. Channels are specific for 1 type of ion or substance– this allows the membrane
to remain selectively permeable
Ribosomes – structures in cytoplasm or on ER where a.a. are linked to make proteins
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Endoplasmic Reticulum (ER) – System of membranes that move proteins and other substances
through the cell
a. Nicknamed “cellular highway”
b. Made of lipid bilayer
c. 2 Types
i. Rough ER– has ribosomes attached– bumpy surface– Proteins pass out of it from a
vesicle– these proteins are used outside the cell
ii. Smooth ER– Lacks ribosomes– has smooth surface– makes lipids and breaks down toxic
substances
Golgi Apparatus – aka Golgi body, golgi complex
a. They receive vesicles with newly made proteins from ER
b. Are the “packaging and distribution” center of the cell
c. Enzymes within the golgi apparatus modify proteins
d. Golgi packs the new proteins in vesicles
e. Vesicles merge with cell membrane to release the contents to the outside of the cell
Lysosomes – small spherical organelles that contain powerful digestive enzymes
a. Help package proteins for use
b. Also help break down unnecessary materials to be recycled
c. Protects cell because it destroys harmful substances
d. Nicknamed the “clean up crew”
Mitochondria – the “Powerhouse”
a. Harvests e- from organic compounds like glucose to make ATP (cellular fuel)
b. This requires oxygen & gives off carbon dioxide
c. Cells with high energy demands have a lot of mitochondria (100’s – 1000’s)
d. Has 2 membranes: outer (smooth) and inner which is folded to increase surface area
e. Has its own DNA
Vacuoles - storage center; stores anything needed by the cell
Centrioles – in animal cells only
a. Mark the opposite sides of cell (poles) during cell division so the chromosomes don’t get
lost while the nuclear membrane is gone and chromosomes are moving
b. Chromosomes are attached to microtubules
c. The microtubules are anchored down by the centrioles
Cell Wall – Plant Cells only
a. Thick boundary made of proteins and carbs (cellulose, polysaccharides)
b. Help support and maintain shape of cell
c. Helps protect cell from damage
d. Connects with adjacent cells
Chloroplasts – photosynthetic cells only (plants)
a. Organelles that use light energy to make carbs from carbon dioxide and water
b. Usually green because they contain green pigment called chlorophyll for photosynthesis
c. Surrounded by its own membrane and has its own DNA
Central Vacuole – cell plants only
a. Stores water, ions, nutrients, and wastes
b. When it is full, it makes the cell rigid due to turgor pressure