1-1 Unit 2: Cell Biology Outcomes A and G Chapters 3, 4, and parts of 7 Prepared by: Wendy Vermillion Columbus State Community College Reformatted for.

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Unit 2: Cell BiologyOutcomes A and G

Chapters 3, 4, and parts of 7

Prepared by: Wendy VermillionColumbus State Community College

Reformatted for use at G.P. Vanier by Ilene Yeomans

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A. Cellular Level of Organization

1. Cells are the smallest unit of life– Exhibit all characteristics of life– Are highly organized– Many become specialized for complex functions

2. Cell theory– All living things are composed of cells– Cells are the functional and structural units of organisms– All cells are derived from previously existing cells

3. Discovery of cellsa) Antonie van Leeuwenhoek- invented the light microscopeb) Robert Hooke- first observed cells in cork (actually saw the cell

walls of dead cells)c) Schleiden and Schwann-proposed cell theory

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Cellular level of organization, cont’d.

4. Cell size– Most cells are smaller than 1 mm in diameter– Surface area/volume ratio determines cell size:

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Cell Size, cont’d. determining surface area to volume

ratios

Cell Dimensions

Surface Area

Volume SA/Vol SA:Vol

1 cm x 1 cm

2 cm X 2 cm

6 cm x 6 cm

Let L be the length of one side

= L x L x 6

= L x L x L

6 1 6 6:1

24 8 3 3:1

216 216 1 1:1

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Cell Size continued

• As the cell size increases, the volume increases faster than the surface area does

• Therefore small cells have a greater surface area to volume ratio than larger cells

• Nutrients from the environment must cross the surface of the cell to enter

• Cells must be small in order for the surface area to be adequate to supply nutrients

• This is one reason why we are made up of lots of cells instead of just one big one

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Cellular level of organization, cont’d.

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B. Eukaryotic cells

• Eukaryotic cells have a membrane-bound nucleus

• Cell Membrane (or Plasma Membrane)

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Eukaryotic cells, cont’d.

• Organelles– Subcellular structures which perform specific

life functions for the cell– Many organelles are found in both animal and

plant cells– Some are found exclusively in plants or

animals• Plants

– chloroplasts, large central vacuole, cell wall

• Animals– centrioles

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Animal cell anatomy

• Fig. 3.2

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Eukaryotic Cells cont’d

• Nucleus– Contains the genetic material (DNA)– Nucleoplasm -semifluid within nucleus– Chromatin -threadlike DNA which has a grainy

appearance– Nucleoli (Nucleolus) -dark regions of

chromatin • These produce rRNA which makes up the two

subunits of ribosomes when combined with protein

– Nuclear membrane - double layered, surrounds nucleus and has large pores

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The Nucleus and Nuclear Envelope

• Fig 3.4

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C. Animal Cell Organelles1. Ribosomes-

– Site of protein assembly (“Protein Synthesis”)– Composed of rRNA and protein subunits– Exist either as free ribosomes (in groups

called polysomes) or bound to endoplasmic reticulum (ER)

• Polysomes produce multiple copies of the same protein for use inside the cell

• Proteins produced at the ER’s ribosomes are destined for export from the cell

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Organelles, cont’d.

2. Rough endoplasmic reticulum (RER)• Complex system of sacs and channels• Has attached ribosomes• Serves as site of assembly of proteins for export• Assembled proteins enter channels for processing

– e.g. addition of sugar chains to form glycoproteins

• Released in vesicles

3. Smooth endoplasmic reticulum (SER)• No ribosomes• Synthesizes lipid products such as phospholipids and

steroids AND is used to detoxify• Product released in vesicles

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The Endoplasmic Reticulum

• Fig 3.5

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Organelles, cont’d.

4. Golgi Apparatus (or Golgi Body)– Packaging and processing center for cell products– Receives the vesicles from ER– Vesicles fuse with Golgi and products are released

inside– Further modification of proteins occurs– Products are packaged into secretory vesicles and

released to travel to the cell membrane– Golgi also produces lysosomes– Easier to remember the functions with MRS Golgi =

» M (modify), R (repackage), S (sort)

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The Endomembrane System

• Fig 3.6

Rough ERSmooth ER

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Organelles, cont’d.

5. Lysosomes– Contain hydrolytic enzymes (very powerful enzymes)– Three functions of lysosomes:

• Intracellular Digestion – lysosome fuses with a vesicle and digests its

contents• Autodigestion

– lysosomes fuse with worn out organelles or cell components and digest them

(e.g. mitochondria)• Autolysis

– lysosomes sometimes called “suicide sacs” because they release their enzymes into the cell causing cell death

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The Endomembrane System

• Fig 3.6

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6. Mitochondria– Site of aerobic cellular respiration

= production of ATP (energy)– Uses oxygen we breathe and food that we eat

to produce energy for every action in and of our body

Up to 38 ATP are made per glucose molecule

Organelles, cont’d.

•6 O2 + C6H12O6 6 CO2 + 6 H2O

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Mitochondrion Structure

• Fig. 3.9

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Organelles, cont’d….

7. Peroxisomes– Specialized vesicles– Smaller than lysosomes– Contain powerful oxidative enzymes

• Use oxygen to strip H’s from certain molecules

• Produce peroxide (H2O2), hence the name

– Role is detoxification• Found in large numbers in liver cells

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Organelles, continued

8. Vaults– Serve as cellular transport vehicles (we

think)– Discovered in the early 1990s (do not show

up with normal staining techniques)– Shaped like octagonal barrels, hollow, 3X size

of ribosomes• Intriguingly, vaults are the same size and shape as

nuclear pores• Research supports vaults’ role in transport from

the nucleus to the cytoplasm• Unknown cargo, BUT are the right size to

accommodate the two ribosomal subunits!

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D. Cytoskeleton• The Cytoskeleton

– Maintains cell shape– Allows cells to move or allows organelles

to move within cells – Made of protein– Components include microfilaments and microtubules:

• Microfilaments are slender fibers that often occur in bundles

e.g. ACTIN which works to contract muscles

• Microtubules protrude from the centrosome and form centrioles, cilia, and flagella

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Eukaryotic cells, cont’d.

• Centrioles see p60

– Short tubules with 9+0 pattern of microtubule triplets

– In animal cells, centrosome is composed of 2 centrioles

– Believed to be involved in microtubule formation including mitotic spindle

• Basal Bodies– Found at the bases of both cilia and flagella – Organize the microtubules in the cilium or

flagellum– Have a 9+0 arrangement of microtubules.

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Centrioles

• Fig. 3.14

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E. Cellular Movement

• Cilia and Flagella– Cilia are generally multiple and hair-like

• Move mucus (phlegm) up the trachea• Move the egg (or zygote) along the oviduct

– Flagella occur single or double and are whip-like

• Propel the sperm

– BOTH have a 9+2 pattern of microtubules

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Structure of Cilia and Flagella

• Fig. 3.15

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The Cell Membrane

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F. Cell (Plasma) Membrane 1. Membrane Structure

– Fluid-Mosaic Membrane Model (FMMM)

– Phospholipid bilayer• Hydrophilic heads face surfaces• Hydrophobic tails face inward

– Proteins • Integral proteins- embedded• Peripheral proteins- surface

– Glycoproteins and Glycolipids• Cell markers (antigens)

– Cholesterol• Changes fluidity of the membrane

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Fluid-Mosaic Model of Membrane Structure

• Fig. 4.1

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Cell Membrane cont’d

• Functions of the Cell Membrane– Functions as a barrier between the cell and its

environment– Regulates what enters or exits the cell

(Regulates transport of substances into and out of the cell)

– Contains receptors that determine how a cell will respond to stimuli in the environment

– Contains proteins that are important in immune responses

– It is a very dynamic, fluid structure

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membrane protein diversity

• Fig 4.2

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G. Permeability of Cell Membrane• Cell membrane is selectively permeable

– Some substances pass through the membrane freely while others do not

• Crossing depends on factors like:i. size and shape of molecule, ii. molecule’s chemical nature (e.g. lipid soluble?)iii. temperatureiv. number of passages (channel proteins, carrier proteins, etc.)

• Rate depends on:i. concentration gradient of substanceii. permeability of membrane to substanceiii. surface area of membraneiv. molecular weight of substancev. distance travelled (thickness of membrane)

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H. Passive Movement

• Passive Mechanisms (of crossing the cell membrane) = no cellular energy required– Kinetic energy drives passive mechanisms– Movement is always from high concentration

to low concentration( = DOWN a concentration gradient)

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Passive mechanisms….

– For instance:

1. Diffusion– The movement of substances from an area of

high concentration to an area of low concentration» Drink crystals in water» Perfume in a room

– The movement of lipid-soluble substances directly through the phospholipid bilayer from an area of high concentration to an area of low concentration» Gases (oxygen and carbon dioxide)» Alcohol

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Process of Diffusion

• Fig. 4.4

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Passive mechanisms….

2. Facilitated Transport– The movement of small, lipid-insoluble

substances such as simple sugars and amino acids across a cell membrane

– Uses a carrier protein – Movement is down a concentration gradient

High

Low

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Facilitated Transport

• Fig. 4.8

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Movement of Molecules Across Cell Membranes

• Table 4.1

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Passive Mechanisms Cont’d

3. Osmosis-– A special case of diffusion = movement of

WATER from an area of low solute concentration to an area of high solute concentration.

» The water moves to an area of high ‘saltiness’ in order to dilute the area

– Water moves through protein-lined pores (“aquaporins”) in the cell membrane.

– Osmotic pressure- force that causes water to move in a direction

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Tonicity

– Isotonic solutions-no change

– Hypotonic solutions-cause cells to swell and burst

– Hypertonic solutions-cause cells to shrink, or crenate

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Osmosis demonstration

• Fig. 4.6

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Osmosis in animal and plant cells

• Fig 4.7

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Permeability of plasma membrane, cont’d.

I. Active Mechanisms= require ATP

1. Active Transport• Uses ATP• Requires a carrier protein• Transports molecules from an area of low

concentration to an area of high concentration= (UP or AGAINST a concentration gradient)

– Example: » sodium/potassium pump in nerve cells» Iodine accumulation in the thyroid gland

Low

High

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Active Transport

• Fig. 4.9

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The Sodium-Potassium Pump

• Fig 4.10

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Active Mechanisms, cont’d.

2. Exocytosis• Requires ATP • Vesicle used• Transports cell products and wastes (big

stuff) out of the cell by vesicle formation– Vesicles fuse with plasma membrane– Products are released – Vesicle membrane becomes part of the

plasma membrane

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Exocytosis

• Fig 4.11

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Active Mechanisms, cont’d

3. Endocytosis• Requires ATP• Vesicle used• Transports substances (big stuff) into the

cell by vesicle formation –membrane invaginates and surrounds a

substance, then pinches off to form a vesicle

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Endocytosis, cont’d

a) Pinocytosis-”cell drinking”

material is liquid or small – Receptor-mediated endocytosis is a specific type

of pinocytosis which occurs in response to receptor stimulation

b) Phagocytosis-”cell eating”

material taken in is large like bacteria or cell debris

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Endocytosis

• Fig 4.12

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POINTS TO PONDER

1. The stomach has two different types of secretory cells. The chief cells secrete pepsinogen (the inactive form of the enzyme pepsin), while the parietal cells secrete hydrochloric acid. Both of these cell types have lots of mitochondria to make ATP. The chief cells use ATP to make pepsinogen. Parietal cells use ATP to actively transport H+ and Cl- from the blood into the cells. Only one of these cell types also has extensive RER and Golgi. Which one and why?

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POINTS TO PONDER

2. One type of the affliction epidermolysis bullosa is caused by a genetic defect that results in production of abnormally weak keratin. Based on your knowledge of the role of keratin, what part of the body do you think would be affected by this condition?

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POINTS TO PONDER

3. Colostrum, the first milk a mother produces, contains an abundance of antibodies (infection-fighting proteins). By what means would you suggest these Ab’s are transported across the cells of a newborn’s digestive tract into his or her bloodstream?

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Clinical-1

Kevin J and his wife have been trying to have a baby for the past three years. On seeking the help of a fertility specialist, Kevin learned that he has a hereditary form of male sterility involving non-motile sperm. His condition can be traced to defects in the cytoskeletal components of the sperm’s flagella. Based on this finding, the physician suspected that Kevin also has a long history of recurrent respiratory tract disease. Kevin confirmed that he has had colds, bronchitis and influenza more frequently than his friends. Why would the physician suspect this?

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Clinical-2

When William H was helping victims in an earthquake-ravaged region, he developed severe diarrhea. He was diagnosed as having cholera, a disease transmitted through unsanitary water supplies that is spread by fecal contamination. The toxin produced by the cholera bacteria leads to the opening of Cl- channels in the lining of the intestine. Cl- then floods into the intestine. How does this account for the diarrhea that is severe enough to kill many who have cholera?