Topic 2: Cells

Cell Theory 2.1.1 Outline the cell theory Cell theory has three main principles 1. All organisms are composed of one or

more cells 2. Cells are the smallest units of life 3. All cells come from preexisting cells

Scientist Contribution to Cell Theory

Robert Hooke First described cells in 1665 by observing cork under a homemade microscope.

Antonie van Leeuwenhoek Observed living cells and called them “little animals”.

Mathias Schleiden Stated that plants were made of “independent, separate beings” called cells.

Theodor Schwann Stated that animals were made of cells.

Evidence for Cell Theory 2.1.2 Discuss the evidence for the cell theory The presence of cells has been proven by the

microscope We have not yet found any organisms not made

of at least one cell Louis Pasteur proved that life does not

spontaneously appearSterilized chicken broth cannot give rise to life unless

exposed to pre-existing cells

1. Pasteur filled two swan-neck flasks with chicken broth. The broth was boiled to sterilize it.

2. Pasteur broke the neck off of one flask, exposing the chicken broth to the air.

3. After some time, the chicken broth exposed to the air had bacterial growth.

Functions of Life 2.1.3 State that unicellular organisms carry

out all the functions of life Metabolism is all the chemical reactions that

occur in an organism All organisms grow In reproduction, hereditary molecules are passed

to offspring Responding to the environment allows

organisms to survive

Homeostasis is maintaining a stable internal environment

Nutrition provides energy

Limiting Cell Size 2.1.6 Explain the importance of the surface area

to volume ratio as a factor in limiting cell size The surface area to volume ratio limits cell size The rate of heat and waste production and the

rate of resource consumption depend on volume Cells with more surface area per unit volume are

able to move more materials in and out of the cell

Large cells have less surface area available to bring in materials and remove wastes

Cells are limited to a size that allows them to function efficiently

Large cells have developed modifications that allow them to functionLong, thin shapes Infoldings and outfoldings to increase surface area

Emergent Properties 2.1.7 State that multicellular organisms show

emergent properties Cells work together to form tissues that perform

a specific function Emergent properties are the properties of the

tissue that could not have been predicted by looking at the individual cells

Cell Differentiation 2.1.8 Explain that cells in multicellular organism

differentiate to carry out specialized functions by expressing some of their genes but not others

Most cells have the ability to specialize into a specific type of cell

This specialization is called differentiation Results from the expression of certain genes but

not others

All cells contain all the genetic information of the whole organism but only express parts of it

Some cells (like nerve and muscle cells) lose the ability to reproduce after differentiation

Cells that are highly specialized require all their energy for their roles in the organismDo not expend valuable energy on division

Others (like skin cells) reproduce indefinitely

Stem Cells 2.1.9 State that stem cells retain the capacity

to divide and have the ability to differentiate along different pathways

Pluripotent stem cells retain the ability to divide and differentiate into any cell type in the organismAlso called embryonic stem cells

Stem cells allow for a continual production of a particular type of tissue

Stem cells can only be identified by their behavior, not appearance

Plants contain stem cells in their meristematic tissue near roots and stem tips

Meristematic tissue contains rapidly reproducing cells that can become different tissue types in the roots and stem

Stem Cell Research 2.1.10 Outline one therapeutic use of stem cells Therapeutic cloning uses stem cells to replace

differentiated cells that were lost to illness or injury

Brain cells could be replaced in Parkinson’s and Alzheimer’s patients

Pancreas cells could be replaced to cure diabetes

Currently, embryonic stem cell research is done in mice

Tissue-specific stem cell research is occurring in humans

Tissue-specific stem cells are found in particular tissues and only produce cells for that tissue

Bone marrow transplants for leukemia patients replace the blood stem cells that have been damaged by cancer

Embryonic stem cell research is controversial because those stem cells come from embryos in IVF labsEmbryo is destroyed during the harvest

Membrane Structure: Phospholipids The plasma membrane is a bilayer composed

largely of phospholipids Made of glycerol (3-C compound)

2 C’s have attached fatty acids3rd C is attached to a polar organic alcohol that bonds

to a phosphate group “like dissolves like” Fatty acids are not water soluble because they

are nonpolar (hydrophobic tails) The phosphate group is polar and water soluble

(hydrophilic heads)

Membrane Diagram 2.4.1 Draw and label a diagram to show the

structure of membranes

Phospholipid

Polar (hydrophilic) head

Nonpolar (hydrophobic) tail

glycoproteinperipheral protein

bilayer

cholesterol

integral protein

Phospholipid Bilayer 2.4.2 Explain how the hydrophobic and

hydrophilic properties of phospholipids help to maintain the structure of cell membranes

The hydrophobic and hydrophilic regions align as a bilayer

The hydrophobic tails are on the inside The hydrophilic heads are on the outside The fatty acid tails do not attract each other

strongly, so the membrane remains fluid or flexible

Flexibility allows for animal cells to:have many shapesPerform exocytosis

The overall structure of the membrane is maintained by water’s ability to form hydrogen bonds

Cholesterol and Proteins Membranes must remain fluid to function

properly Cholesterol molecules are embedded in the

hydrophobic regions Cholesterol helps maintain membrane fluidity

during temperature changes Integral proteins have both hydrophobic and

hydrophilic regions and can span the membrane Peripheral proteins are bound to the membrane

surface

Membrane Proteins 2.4.3 List the functions of membrane proteins Hormone binding sites

Proteins have specific shapes exposed that fit specific hormones

Attachment causes a shape change in the protein, which relays a message to the cell

Enzymatic action These proteins are often grouped to perform a

sequence of metabolic reactions (pathway)

Cell adhesionProteins hook together to make temporary or

permanent connections called junctions Cell-to-cell communication

Involve proteins with attached carbohydrates (glycoproteins)

Serve as labels Channels for passive transport

Materials move through the channel from areas of high concentration to areas of low concentration

Pumps for active transportShuttle substances by changing shape and using ATP

Hormone receptor

Enzymatic pathway

Protein channel (passive transport)

ATPADP + Pi

Protein channel (active transport)

Diffusion and Osmosis 2.4.4 Define diffusion and osmosis. Diffusion: the movement of a substance from

areas of high concentration to low concentration Type of passive transport (no ATP)

Osmosis: the movement of water particles across a partially permeable membrane from high to low concentration

Type of passive transport The concentration gradient in osmosis is based

on the solute concentration

A hyperosmotic solution has a high concentration of solutes and a low concentration of water

A hypo-osmotic solution has a low concentration of solutes and a high concentration of water

Water flows via osmosis from a hypo-osmotic solution to a hyperosmotic solution

Osmosis occurs until the solutions on both sides of the membrane are equal (iso-osmotic)

Passive Transport 2.4.5 Explain passive transport across

membranes by simple diffusion and facilitated diffusion

In simple diffusion, substances move along a concentration gradient

Substances other than water move between phospholipids or through protein channels

In facilitated diffusion, a non-channel protein carrier changes shape to allow a substance other than water to move along a concentration gradient

Passive transport is influenced by the size and charge of the substances

Small and nonpolar move across membranes easily

Active Transport 2.4.6 Explain the role of protein pumps and ATP

in active transport across membranes In active transport, ATP is required Substances move against a concentration

gradient Requires carrier proteins that are specific for the

particles being transported Seen best in the sodium-potassium pump

The concentration of sodium is greatest outside the cell, whereas potassium is greatest inside

Sodium is pumped out of the cell and potassium is pumped in

1. Three sodium ions are bound to a membrane protein

2. The binding of sodium causes ATP to change the shape of the protein through phosphorylation

3. The shape change forces the sodium out of the cell

4. Two potassium ions bind to a different site on the same protein

5. Dephosphorylation causes the protein to change shape again, forcing the potassium into the cell

Endo- and Exocytosis 2.4.7 Explain how vesicles are used to transport

materials within a cell between the rough ER, Golgi, and plasma membrane

2.4.8 Describe how the fluidity of the membrane allows it to change shape, break and re-form during endocytosis and exocytosis

Endocytosis allows macromolecules to enter the cell

Exocytosis allows macromolecules to leave the cell

Both depend on the fluidity of the membrane In endocytosis, the plasma membrane is pinched

off to enclose the macromoleculeThe membrane changes shape to make a vesicle,

which brings the substance into the cellPhagocytosis if the molecule is solidPinocytosis if the molecule is liquid

The ends of the membrane reattach because of its hydrophobic and hydrophilic properties

Exocytosis begins in the ribosomes on the rough ER

1. Protein made by the ribosome enters the lumen of the ER

2. Protein exits the ER in a vesicle and enters the cis side of the Golgi apparatus

3. The protein is modified in the Golgi and exits the trans side in a vesicle

4. The vesicle fuses with the plasma membrane and secretes its contents

- - - - Cell membrane

Rough endoplasmic reticulum

Secretory vesicle

Tr a sportves1c e / - - - - - - - Golgi

apparatus

ttp:/lwvvw.fredonia .edu/bio241/imagesl5 .19_ER_and_Golgi .jpg