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2.1 CELL THEORY (BIOLOGY HL) 21/10/201012:31:00

Introduction to the Cell Theory:

Cells are the smallest unit of life and nothing smaller can survive

independently.

All living things consist of cells, although the smallest organisms mayconsist only of one cell.

All cells come from pre-existing cells, by division, and therefore new

cells cannot be constructed from non-living chemical substances.

Proof that All Living Things Consists of Cells

Since the time of Robert Hooke, numbers of tissue samples from

many different organisms have been examined using microscopes

and all consists of cells.

Proof that Nothing Smaller Than Cells Can Survive Independently

Cells have been burst open to examine various subunits and

organelles, yet the subunits of cells cannot survive long

independently.

Proof that All Cells derive from Pre-existing Cells

Experiments have been conducted and when all cells are dead, no

more cells are produced. Cells cannot derive from non-livingsubstances, only from pre-existing cells.

Unicellular Organisms

Nutrition- obtaining food, to provide energy and the materials

needed for growth.

Metabolism- chemical reactions inside the cell, including cell

respiration to release energy.

Growth- an irreversible increase in size.

Sensitivity- perceiving and responding to changes in the

environment.

Homeostasis- keeping conditions inside the organisms within

tolerable limits.

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Reproduction- producing offspring either sexually or asexually.

o The structure of single cells of unicellular organisms are

therefore more complex than most cells as they have to

perform all of the tasks listed above! Examples of single celled

organisms includeAmoeba and Paramecium.

Measurements

mm- millimeter, m- micrometer, nm- nanometer

Comparing measurements:

o 0.001 mm = 1 m = 1000 nm

Magnification Formula

Magnification= (size of image/size of specimen)

Sizes

Molecules 1 nm

Cell Membranes 10 nm

Virus 100 nm

Bacteria 1000 nm or 1

Eukaryotic Organelles 10,000 nm or 10 m

Eukaryotic Cells 100,000 nm or 100 m

Limiting Cell Size

All cells grow in size

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All cells have a maximum size to which they can grow to.

o They may divide to form two cells.

o They may stop growing.

o They may die.

Cells are limited by the need to get oxygen (O2) and nutrients to allparts of the cell, as well as to get rid of wastes from all parts of the

cell. Heat from chemical reaction must be released.

Some substances may be transported within the cell but many only

more by diffusion (eg. Oxygen and Carbon Dioxide diffusion

means to spread [concentration] evenly, from [high][low].

Diagram:

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Movement of these substances and also heat must be across the cell

membrane, by passive means (diffusion of particles; conduction,

connection, radiation of heat).

The cell surface membrane must have enough surface area to servicethe volume of the cell.

*the key factors regulating cell size limit is the ratio of the surface

area to the volume of the cell (surface area : volume)

Formula to Calculate the Surface Area, Volume and Ratio of Cells

Surface Area 4r2

Volume 4/(3r3)

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Ratio (4r2)/( 4/(3r3))

Multicellular Organisms

Some multicellular organisms live together in colonies (for example:

a type of algae called Volvox aureus). Multicellular Organisms: Organisms consisting of a single mass of

cells fused together.

Multicellular organisms differentiate to carry out specialized functions

by expressing some of their genes but not others.

Differentiation

The development of cells in different ways to perform different

functions. (More than one type of cell).

This involves each cell type using some of the genes in it nucleus,

but not others. When a gene is being used in a cell, we say that the

gene is being expressed.

Expressed : To activate or show, in this case activating or switching

on the gene of the cell to function.

In other words, the gene is expressed and the information in it is

used to make a protein or other gene products.

Stem Cells Definition: Cells that have the capacity to self- renew and

differentiate (develop into many different cell types in the body

during early life and growth).

At an early stage (3-5 days) the whole of the human embryo consists

of stem cells, but gradually the stem cells in the embryo become

committed to differentiating n a particular way. Once committed, a

cell may divide about six more times, though now the differentiate in

the same way (only producing one type of cell), therefore no longer

being a stem cell.

Found in the blastocyst of the embryo during a young age. In adults,

they are usually found in tissues.

Stems Cell retain the capacity to divide and have the ability to

differentiate along different pathways.

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In addition, in many tissues they serve as a sort of internal repair

system, dividing essentially without limit to replenish other cells as

long as the person or animal is still alive.

When a stem cell divides, each new cell has the potential either to

remain a stem cell or become another type of cell with a morespecialized function, such as a muscle cell, a red blood cell, or a brain

cell.

Therapeutic Use of Stem Cells

First, they are unspecialized cells capable of renewing themselves

through cell division, sometimes after long periods of inactivity.

Second, under certain physiologic or experimental conditions, they

can be induced to become tissue- or organ-specific cells with special

functions. In some organs, such as the gut and bone marrow, stem

cells regularly divide to repair and replace worn out or damaged

tissues. In other organs, however, such as the pancreas and the

heart, stem cells only divide under special conditions.

Example: Parkinsons disease is caused by the loss of neutrons or

other cells in the nervous system. Stem cells can replace the lost

cells.

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2.2 PROKARYOTIC CELLS (BIOLOGY HL) 21/10/201012:31:00

Diagram of Escherichia Coli (E. Coli)

A- Flagella B- Plasmid C- Ribosome D- Pili E- Nucleoid (circular

DNA) F- Capsule G- Cell Wall H- Plasma Membrane I- Cytoplasm J-

Nucleus

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Flagella

Structure protruding from cell wall with a corkscrew shape

Base is embedded in the cell wall

Using energy, flagella can be rotated to propel the cell from one areato another

Unlike eukaryotic flagella, they are solid and inflexible

Ribosomes

Synthesizes proteins, and are very small and great in number

Pili

Protein filaments protruding from the cell wall

Can be pulled in or out by a ratchet mechanism

Used for cell to cell adhesion

Used when bacteria stick together to form aggregations of cells

Used when two cells are exchanging DNA during a process called

conjugation

Nucleoid

Region of cytoplasm containing the genetic material (usually one

molecule of DNA)

DNA molecule is circular and naked (not associated with protein)

Total amount of DNA is smaller than Eukaryotes

Due to less concentration of protein and ribosomes, the nucleoid isstained less densely than the rest of the cytoplasm

Cell Wall

Always present, protects the cell, maintains its shape and prevents

the cell from bursting

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Composed of peptidoglycan

Plasma Membrane

A Thin layer composed of phospholipids, pushed up against the inside

of the cell wall in healthy cells

Partially Permeable, allowing and controlling entry and exit ofsubstances

Can also pump substances in or out by active transport

Produces ATP by aerobic cell respiration

Cytoplasm

Fluid (composed of water with many dissolved substances) filling the

space inside the plasma membrane

Contains many enzymes and ribosomes

Does not contain any membrane- bound organelles

Carries out the chemical reactions of metabolism

BE FAMILIAR WITH ULTRASTUCTURE OF E. COLI. DRAW DIAGRAM:

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Watch to understand Binary Fission

http://www.youtube.com/watch?v=6Zv5YYbLPnk&feature=related

Binary Fission (only occurs in Prokaryotic cells) asexual

behavior Prokaryotic cells divide by binary fission

Steps in Binary Fission

o 1st: The nucleoid replicates itself while still being attached to

the old mesosome.

o 2nd: The cell membrane grows between the two, still attached,

necleoids, pushing them to opposite sides.

o 3rd: Cytoplasm constricts in between the two mesosomes or

nucleoids to form two new daughter protoplasts each having a

nuclear body. (This simple type of cell division is called

amitosis).

o 4th: A double wall is created in between the funnel connecting

the two daughter protoplasts diving the original sex into two

separate identical cells.

During binary fission, the single DNA molecule replicates and both

copies attach to the cell membrane. Next, the cell membrane

extends between the two DNA molecules. Once the bacterium just

about doubles its original size, the cell membrane begins to pinchinward. A cell wall then forms between the two DNA molecules

dividing the original cell into two identical cells.

http://www.youtube.com/watch?v=6Zv5YYbLPnk&feature=relatedhttp://www.youtube.com/watch?v=6Zv5YYbLPnk&feature=related

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2.3 EUKARYOTIC CELLS (BIOLOGY HL) 21/10/201012:31:00

Diagram Liver Cell

Functions

Nucleus:

o Where almost all of the genetic material is stored.

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o Where DNA is replicated and transcribed.

o Where mRNA is modified before export to the cytoplasm.

o The nuclear membrane is double and has pores through it.

Uncoiled chromosomes are spread throughout the nucleus and

are called chromatin.o Chromatin are often densely stained areas around the edge of

the nucleus.

Rough Endoplasmic Reticulum:

o Consists of flat membrane sacs called cisternae.

o Membrane- bound ribosomes are attached to the outside of

these cisternae.

o Main function: To synthesize protein for secretion from the cell.

o Protein synthesized by the ribosomes of the rER passes into

the cisternae and is then carried by vesicles, which buds off

and are moved to the Golgi Apparatus.

Golgi Apparatus:

o Consists of flat membrane sacs called cisternae without any

ribosomes attached, not as long or curved and do not have

many vesicles nearby.

o Main function: Processes the protein brought in vesicles from

the rER.

o Most of these proteins are then carried in vesicles to theplasma membrane for secretion.

Lysosomes:

o Approximately spherical with a single membrane.

o Formed from Golgi Apparatus and contains high concentrations

of protein, making them highly densely stained in electron

micrographs.

o Contains enzymes that can break down ingested food in

vesicles or break down organelles in the cell or even the whole

cell.

Mitochondria:

o Double membrane surrounds it, with the inner of these

membranes invaginated to form structures called cristae.

o The fluid inside is called matrix.

o Shape is variable, but is usually: spherical or ovoid.

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o Function: produces ATP for the cell by aerobic cell respiration.

o Fat is digested here if it is being used as an energy source in

the cell.

Free Ribosomes:

o Appear as dark granules in cytoplasm and are not surroundedby a membrane.

o About 20 nm in diameter.

o Synthesize protein, releasing it to work in the cytoplasm, as

enzymes, or in other ways.

o Ribosomes are constructed in a region of the nucleus called the

nucleolus.

BE FAMILIAR WITH ULTRASTUCTURE OF LIVER CELL. DRAW DIAGRAM:

Differences in Prokaryotic and Eukaryotic Cells

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Prokaryotic Cells Eukaryotic Cells

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1. Naked DNA

2. DNA in Cytoplasm

3. No Mitochondria

4. 70S ribosomes

5. No internal membranes6. Golgi Apparatus NOT Present

7. No Lysosomes Present

8. One Circular strand of DNA/RNA

1) DNA associated with proteins

2) DNA enclosed in nuclear envelopme

3) Mitochondria available

4) 80 S ribosomes

5) Have internal membranes thatcompartmentalize their function

6) Golgi Apparatus Present

7) Contains Lysosomes

8) Many Chromosomes Present

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Differences Between Animal and Plant Cells

Animal Cells

o No Cell Walls Present, Only has Cell Membrane

o Lysosomes occur in cytoplasmo No Chloroplasts

o Round (irregular shape)

o No Plastids

Plant Cells

o Cell Wall and Cell Membrane Present

o Lysosomes usually are NOT evident

o Contains Chloroplasts (have to make their own food)

o Rectangular (fixed shape)

o Plastids available

Extracellular Components

Animal Cells secrete glycoproteins that form the extracellular matrix.

This functions in support, adhesion and movement. The matrix glues

the cells in animal tissues together, supports tissues and also helps

the move of, for example in tissues, tendon and ligaments.

The plant cell wall maintains cell shape, prevents excessive water

uptake, and holds the whole plant up against the force of gravity.

Definition: Components that pass through the membrane and formpart of the structure outside.

Extracellular components include cellulose, teeth, bone cartilage,

and connective tissue. To sum it up, extracellular components are

material outside the cell membrane.

Two basic roles: plant cell wall and glycoproteins.

Intracellular Components

Definition: Anything inside the plasma membrane.

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2.4 MEMBRANES (BIOLOGY HL) 21/10/201012:31:00

Fluid Mosaic Model of Membrane Structure

The membranes are not rigid. The are fluid in the molecules in it may move

around to a certain degree. Cholesterols function to increase the fluidity. Fluid

and moves around a lot.

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Maintaining Structure of Cell Membranes

All Cell membranes consist of Phospholipid Bilayer.

The heads (outer parts) are hydrophilic.

The tails (inner parts) are hydrophobic.

This maintains its structure as the heads will always face outwards inboth directions, as the tails with always face inwards in one direction.

Functions of Membrane Proteins (Integral or Peripheral

Proteins)

Membrane Channels channels for passive transport to allow

hydrophilic particles across by facilitated diffusion

Pumps pumps for active transport which uses ATP to move

particles across the membrane.

Hormone Binding Site also called hormone receptors.

Immobilizes Enzymes with the active site on the outside, for

example in the small intestines.

Cell to Cell Adhesion to form tight junctions between groups of

cells in tissues and organs.

Cell to Cell Communication For example, receptors for

neurotransmitters at synapses.

Diffusion All particles randomly vibrate.

In fluids (liquids + gases) these particles are free to move.

Therefore, particles in high concentration will move towards areas of

lower concentration.

o Diagram:

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Osmosis

A kind of diffusion (diffusion with water)

Random movement of water molecules across a membrane (i.e. a

semi- permeable membrane Not everything can pass through

membranes, but water can).

All cells are permeable to water, but not permeable to some other

substances. If it were permeable to everything, cells would be

useless as everything would mix.

o Diagram:

Hypertonic Overly Concentrated compared or to another solution.

Hypotonic Less/Not as concentrated compared or to anothersolution.

Isotonic Solution is evenly concentrated in all areas.

Water always diffuses across membranes towards the hypertonic

solution. Why? So that the cell increases in size and the particles are

EVENLY SPACED. This happens inside and outside of the cell.

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Passive Transport Movement of substances across a cell

membrane that requires no energy output from the cell.

Simple Diffusion

o Many small molecules can diffuse across membranes without

assistance (Oxygen, Carbon Dioxide, Water).o Always in the direction of the concentrated gradient ([high] to

[low]).

Facilitated Diffusion

o Integral proteins act as channels.

o They allow certain substances to pass through

o Particles must go from [high] to [low].

o Diagram Situation:

Active Transport Movement across the membranes that

require energy from the cell Usually ATP.

Pumps

o Integral membrane protein pump substances against theconcentration gradient.

o ATP is used. Diagram Below:

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Exocytosis

o Vesicles pinch off golgi apparatus.o Migrate to plasma membrane.

o Fuse with plasma membrane.

o Release contents outside cell.

This is how substances are secreted outside cell. E.g.:

Digestive Enzyme Hormone.

o Diagram the process (look at change in shape during

Exosytosis):

Endocytosiso Invigination of plasma membrane or extending of pseudopodia.

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o A Vesicle forms.

o The vesicle separates from the plasma membrane.

o Diagram Process (look at change in shape during Endocytosis):

BOTH USES ATP:

Phagocytosis Big, Solid Stuff Engulfed, Pinocytosis Only liquid

Engulfed.