understanding homeostasis at the cellular level

Understanding Homeostasis at the Cellular Level

CELL THEORY AND STRUCTURE

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What are the 3 parts of the Cell Theory?

1. All living things are made of cells2. Cells are the basic unit of structure and

function in an organism (basic unit of life)3. Cells come from the reproduction of

existing cells (cell division)

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History of Cells & the Cell Theory

In 1665,Hooke is responsible for naming cells

In 1673, Leeuwenhoek was first to view living organisms in pond water

In 1838, Schleiden concluded that all plants were made of cells

In 1839, Schwann concluded that all animals were made of cells

In 1855, Virchow observed, under the microscope, cells dividing and reasoned that all cells come from other pre-existing cells by cell division

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Remember Endosymbiotic Theory

In 1970,Lynn Margulis, provided evidence that some organelles within cells were at one time free living cells themselves – this is called Endosymbiotic Theory

Chloroplasts and mitochondria were the organelles she pointed to as evidence of this theory

Chloroplast and Mitochondria have their own DNA which is different from the DNA of the cell

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Number of Cells

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• Unicellular – composed of one cell

Ex: bacteria, yeast

• Multicellular - composed of many cells that may organize

Ex: butterfly, flower

Prokaryotes

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• Have a nucleoid region contains the DNA (no nucleus)

• Have a cell membrane & cell wall

• Contain ribosomes to make proteins in their cytoplasm

Eukaryotic Cell

Contain 3 basic cell structures:

Nucleus (containing DNA)

Cell Membrane Cytoplasm with

organelles Organelles have

specific functions 7

Two Main Types of Eukaryotic Cells

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Plant CellAnimal Cell

Lysosome

Contain digestive enzymes

Use Active Transport to trap and break down food an worn out cell parts

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Nucleolus

Inside nucleus

Produces the ribosomes that make proteins

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Smooth & Rough Endoplasmic Reticulum

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• Smooth ER - lacks ribosomes & detoxifies poisons and synthesizes lipids

• Rough ER - has ribosomes on its surface & makes proteins to EXPORT

Mitochondria

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• Site of Cellular respiration – the capturing of energy from food

• Breaks down glucose to produce energy ATP

Plant Cell Organelles

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• Process called photosynthesis occurs here

Chloroplas

t

Plant Cell

• Made of cellulose

• Found in plant cells

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Cell wall

Plant Cell Organelles

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Have a large central vacuole

Vacuole

Animal Cell Organelles

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glycogen granule

• Glycogen is stored in the cytoplasm of animal cells for food energy

Animal Cell Organelles

Near the nucleus in an animal cell

Help cell divide17

Differences between plant cells and animal cells

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Animal cells Plant cells

Relatively small in size

Irregular shape

No cell wall

Relatively large in size

Regular shape

Cell wall present

Differences between Plant Cells and Animal Cells

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Animal cells Plant cells

Vacuole small or absent

Glycogen as food storage

Nucleus at the center

Large central vacuole

Starch as food storage

Nucleus near cell wall

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The Cell Membrane

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Cell or Plasma Membrane

Composed of double layer of phospholipids and proteins

Controls what enters or leaves the cell Surrounds outside of ALL cellsOutsideof cell

Insideof cell(cytoplasm)

Cellmembrane

Proteins

Proteinchannel Lipid bilayer

Carbohydratechains

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Semipermeable Membrane

The cell membranes of all cells are selectively permeable

This means that some materials can pass easily through the membrane

Examples: H20, CO2 and O2

This also means that some materials cannot pass easily through the membrane

Examples: glucose and salts

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Cell Membrane Proteins

Proteins help move large molecules or aid in cell recognition

Peripheral proteins are attached on the surface (inner or outer)

Integral proteins are embedded completely through the membrane

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Other Functions of Plasma Membrane

Provide a binding site for enzymes

Interlocking surfaces bind cells together (junctions)

Contains the cytoplasm (fluid in cell)

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Phospholipids

Phospholipid bilayer makes up the cell membrane

Contains a polar head (attracts H2O) and 2 non-polar fatty acid tails (repels H2O)

How is a phospholipid different from a triglyceride?

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Fluid-Mosaic Model of the Cell

Fluid: individual phospholipids and proteins can move side-to-side within the layer, like a

liquid.

Mosaic: the pattern produced by the scattered proteins on the surface of the cell when the

membrane is viewed from above.

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Solubility of the Membrane

Materials that are soluble in lipids can pass through the cell membrane easily

Ex: Oxygen, carbon dioxide, and water

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Cell Transport Mechanisms

Passive Transport Does not

require cellular energy

Types:1. Simple

Diffusion2. Osmosis3. Facilitated

Diffusion

Active Transport Does require

cellular energy

Types:1. Membrane

Pumps2. Endocytosis3. Exocytosis

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Passive Transport

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Simple Diffusion Movement of materials from a region of

high concentration to a region of low concentration

Materials are moving down/with their concentration gradient

Example:

Oxygen diffusing into a cell and carbon dioxide diffusing out using kinetic energy

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Simple Diffusion

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Osmosis Osmosis is the passive transport (diffusion) of

water across a membrane Moves from a region of HIGH water potential

(low solute) to a region of LOW water potential (high solute)

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Osmosis The purpose of osmosis is to

balance out the concentration of materials between the environment inside of the cell and the environment outside the cell

Water moves because the other materials cannot

This allows the cell to be in equilibrium - balance

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Types of Solutions a Cell May be Found In

Solution - a liquid mixture in which the minor component (the solute) is uniformly distributed within the major component (the solvent).

Examples – salt water or glucose solutions; solutes are salt or glucose, solvent is water

Types of solutions:1. Isotonic2. Hypotonic3. Hypertonic

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Isotonic Solution10% NaCL90% H2O

ENVIRONMENT

CELL

10% NaCL

90% H2O

Q: What is the direction of water movement in an

isotonic solution?

A: No net movement (water molecules moving equally back

and forth)

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Hypotonic Solution

ENVIRONMENT10% NaCL90% H2O

20% NaCL

80% H2O

CELL

Q: What is the direction of water

movement in a hypotonic solution?

A: Water moves into

the cell

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Hypertonic Solution

ENVIRONMENT

CELL

15% NaCL85% H2O

5% NaCL95% H2O

Q: What is the direction of water

movement in a hypertonic solution?

A: Water moves out of the cell.

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Hypertonic or Hypotonic?

Hypotonic solution will result in cytolysis – cell bursts from build up of water inside cell

Hypertonic solution will result in plasmolysis – cell membrane pulls away from the cell wall in plant, fungal or bacterial cells

Plant cells prefer a hypotonic environment

Animal cells prefer an isotonic environment

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Label the pictures: hypotonic, hypertonic, isotonic

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Facilitated Diffusion Uses transport

proteins to move materials from high to low concentration

Examples: Glucose or amino acids moving from blood stream into a cell.

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Active Transport

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Proteins and Cell Membrane Function

Types of Membrane Proteins:

1. Structural2. Cell recognition3. Communication4. Transport:

a. Channel proteins are embedded in the cell membrane & have a pore for materials to cross

b. Carrier proteins can change shape to move material from one side of the membrane to the other

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Channel Proteins

Channel proteins actas bridges to

allow materials to pass across

the membrane

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Carrier Proteins

Some Carrier proteins do not extend through the membrane.

They bond and drag molecules

through the lipid bilayer

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Protein Pumps Cells need a steady supply of sodium (Na+),

potassium (K+), calcium (Ca2+) and hydrogen (H+) in order to function correctly

Protein pumps that span the cell membrane are powered by ATP and supply these materials to the cell on demand

This requires a steady supply of ATP Materials are moving from and area of low

concentration to an area of high concentration

They are moving up/against their concentration gradient

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Sodium Potassium Pump

3 Na+ pumped out for every 2 K+ pumped in

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Types of Active Transport using

Vesicles Q: What is a vesicle? A: A small bubble within a cell surrounded

in its own lipid bilayer. Q: What is the function of a vesicle? A: Vesicles are involved in:

• Metabolism• Transport of materials• Enzyme storage

Types of active transport using vesicles:• Exocytosis• Endocytosis

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Exocytosis

Exocytosis -using a vesicle to move big stuff out of the cell

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Exocytosis How it works:1. Vesicle is formed around some sort of material

made by the cell (like proteins or hormones)2. Vesicle is released and travels toward cell

membrane3. Vesicle fuses with cell membrane4. Vesicle expels materials to the outside of the cell

membrane

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Endocytosis

Large amount of materials move into the cell by one of two forms of endocytosis:

Pinocytosis - Materials dissolve in water to be brought into cell Called “Cell Drinking”

Phagocytosis - Used to engulf large particles such as food, bacteria, etc. into vesicles. Called “Cell Eating” White blood cells eat foreign substances in your

body this way

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Endocytosis

Pinocytosis