topic 2: cells. cell theory 2.1.1 outline the cell theory cell theory has three main principles...
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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
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