Unit 2: Cells

Prokaryotes vs Eukaryotes

Prokaryotic Cells
- bacterial cells
- lack membrane-bound organelles and nucleus
- small and unicellular (single cells)
- relatively basic cells and have very little cellular organization
- single, circular chromosome of naked DNA
- have a cell wall, but different to cell walls that some eukaryotes have
Eukaryotic Cells
- have membrane-bound organelles and nucleus
- plant cells, animal cells, fungal cells, and protists
- large and may exist as a single cell or as part of a multicellular organism
- multiple linear chromosomes consisting of DNA and associated proteins
- more complex than prokaryotic cells (more structure and internal organization)

Osmosis

What is osmosis?
osmosis is the diffusion of water through a selectively permeable membrane
*a selectively permeable membrane lets some, but not all molecules pass through, example: plasma membrane
- osmosis is a passive process (requires no energy to occur)
- the water moves from high to low concentrations
- the water moves freely through pores (ex: water moved into the dialysis bag)
- the solute is too large to move across (ex: glucose stayed in the dialysis bag)
What are the effects of osmosis?
water is so small and there is so much of it that the cell can’t control its movement through the cell membrane
Isotonic Solution
isotonic is when concentration of solutes in the solution is equal to the concentration of solutes inside the cell
this results in the water moving equally in both directions and the cell remains the same size (dynamic equilibrium)
Hypotonic Solution
hypotonic is when the solution has a lower concentration of solutes and a higher concentration of water than inside the cell (low solute; high water)
this results in the water moving from the solution to inside the cell and the cell swells and bursts open (cytolysis)
Hypertonic Solution
hypertonic is when the solution has a higher concentration of solutes and a lower concentration of water than inside the cell (high solute; low water)
this results in the water moving from inside the cell into the solution and the cell shrinks (plasmolysis)

Diffusion

diffusion is the random movement of particles from an area of high concentration to an area of low concentration
- diffusion continues until all molecules are evenly spaced (equilibrium is reached)
note: molecules will continue to move around but stay spread out
- passive transport, no need for energy to occur
Facilitated diffusion
facilitated diffusion is the diffusion of specific particles through transport proteins found in the membrane
- transport proteins are specific: they “select” only certain molecules to cross the membrane
- transports larger or charged molecules
- passive transport

Endocytosis

endocytosis is taking in bulky materials into a cell
- uses energy (active transport)
- cell membrane in-folds around food particle - “cell eating”
Steps
1. materials that are to be collected and brought into the cell are engulfed by an invagination of the plasma membrane
*invagination - being turned inside out or folded back on itself
2. vesicle buds off from the plasma membrane
3. the vesicle carries molecules into the cell, the contents may then be digested by enzymes delivered to the vacuole by lysosomes
Two main types: phagocytosis and pinocytosis
phagocytosis describes the engulfment and transport of solid particles into the cell
pinocytosis describes the engulfment of liquids or fine liquid suspensions into the cell

Exocytosis

exocytosis forces material out of the cell in bulk
- cell changes shape - requires energy (active transport)
- hormones or wastes released from cell
Steps
1. vesicles carrying molecules for export move to the perimeter of the cell
2. vesicle fuses with the plasma membrane
3. the contents of the vesicle are expelled into the inter-cellular space (which may be into the blood stream)  

Plasmolysis
Plasmolysis is when the cell shrinks as a result of a loss of water from a cell

Active transport 

in active transport, cells use energy (ATP)
- actively moves molecules to where they are needed
- movement from an area of low concentration to an area of high concentration (low → high)
- some are protein pumps, endocytosis (phagocytosis/minocytosis), and exocytosis
*protein pumps transport proteins that require energy to do work (the proteins change shape to move molecules which require energy)

Golgi Apparatus
 
description: Flattened, disc-shaped sacs of the Golgi are stacked one on top of each other, very near, and sometimes connected to the ER
made of: closely stacked, flattened sacs (membranes)
function: vesicles bud off from the Golgi and transport protein products away
- the Golgi apparatus is the packaging department of the cell
- associated with the process of secretion
→ it produces secretory vesicles (small membrane-bound sacs) that are used to store useful chemicals, prepare substances for movement out of the cell (ex: hormones, proteins), or to package digestive enzymes
- produces lysosomes and compartmentalizes the modification
simplified description: packages and modifies substances made in ER to be stored in cells or excreted from cell - spit off vesicles
plants or animal cells: they occur in both
location: in the cytoplasm

Lysosomes

function: membrane-bound lysosomes contain enzymes for the destruction of wastes and foreign material
- peroxisomes are the site for destruction of the toxic and reactive molecule, hydrogen peroxide (formed as a result of some cellular reactions)
simplified: stores digestive enzymes for breaking down food or cell particles
made of: membrane-bound sac containing enzymes
associated with the process of autolysis
→ lysosomes contain powerful digestive enzymes that destroy unwanted cell organelles and foreign objects brought into the cell
plants or animal cells: in animal cells, typically; not widely observed in plants
location: throughout cell, attached to food vesicles (small, temporary vacuoles) or injured cell parts

Endoplasmic Reticulum  
Rough ER
description: have ribosomes attached to the surface
function: protein is synthesized directly into the space within the ER membranes
- also involved in membrane synthesis, growing in place by adding proteins and phospholipids
- chemically modify (help forms structure, add other macromolecule components) proteins made on ER surface that are exported or are part of membrane proteins
simplified: proteins are made here
made of: folding membranes
- has ribosomes attached to surface to give “rough” appearance
associated with the process of protein synthesis
plants or animal cells: both plant and animal cells
location: surrounds nucleus, throughout cell

Smooth ER
description:
function: transport system and involved in cell metabolism
- synthesizes lipids and biological membranes
associated with the process of lipid and steroid synthesis
simplified: makes lipids and phospholipids
made of: folding membranes
contains: enzymes that aid in functions and detoxification
plants or animal cells: both plant and animal cells
location: throughout cell

Plasma membrane 
the membrane surrounding a cell is called the plasma membrane
- it forms the boundary that separates the living cell from its non-living surroundings
It is responsible for 6 main functions:
1. to isolate and protect the cell’s cytoplasm from the external environment
2. to regulate the exchange of essential substances between the cytoplasm and external environment
3. to receive chemical messages and relay the messages to the inside of the cell
4.to facilitate communication between cells, allowing for coordination of cellular activities and responses to stimuli
5. to provide structural support and maintain the shape of the cell
6. to act as a barrier to harmful substances while permitting the passage of nutrients and waste products

Hooke  
- devised the compound microscope in 1665
- was the first to coin the name “cell” after he observed the angular spaces that he saw in a thin section of a cork

Schleiden
- all plants are made of cells

Schwann
- all animals are made of cells

Antoine van Leeuwenhoek
- designed and built the single lens microscope which provided a magnification of 270 times
- bacteria, protozoa, human blood cells, and sperm atozoa were discovered using them

Virchow
all cells come from pre-existing cells

Phospholipids

 Fluid Mosaic Model

Ion Pump  

Microscope usage 

Bubble Lab - significance