Chapter 3: Cells Flashcards
Cell Theory
- The cell is the smallest unit of life
- All organisms are made of one or cells
- Cells only arise from other cells (mitosis) with the exception of sperm and ovum cells which arise by meiosis
The principle of Complementarity of structure and function
The activities of cells are dictated by their shapes, and by the types and relative numbers of the subcellular structures they contain.
-A cells shape reflects its function
3 main parts to a human cell
- Plasma Membrane
- Cytoplasm
- The nucleus
Plasma membrane
- A main part to a human cell (1/3)
- The outer boundary of the cell, which acts as a selectively permeable barrier
Cytoplasm
- A main part to a human cell (2/3)
- The intracellular fluid packed with organelles
The Nucleus
- A main part to a human cell (3/3)
- An organelle that controls cellular activities
Extracellular Materials
Are substances contributing to body mass found outside the cells.
- This includes:
- Extracellular Fluid (ECF)–interstitial fluid; blood plasma; and cerebrospinal fluid
- Cellular Secretions
- Extracellular Matrix
Extracellular Fluid (ECF)
- ECF dissolves and transports substances in the body.
- Includes interstitial fluid and cerebrospinal fluid
Interstitial Fluid
- Is the fluid in tissues that bathes all of our cells, has endless major roles to play
- think about it like a nutritious soup, containing ingredients like: amino acids, sugars, fatty acids, regulatory substances, and wastes
Cellular Secretions
- Extracellular Materials
- These secretions include substances that aid in digestion (intestinal and gastric fluids) and some that act as lubricants (saliva, mucus, and serous fluids)
Extracellular Matrix
- The most abundant extracellular material
- Composed of proteins and polysaccharides (jelly-like substances)
- Secreted by the cells
- These molecules self assemble into an organized mesh in the extracellular space, where they serve as a universal “CELL GLUE” that helps bind body cells together
- Particularly abundant in connective tissues
Plasma Membrane
- Separates 2 of the body’s major fluid compartments:
- intracellular fluid within cells
- extracellular fluid outside cells
The Fluid Mosaic Model
- Depicts the PLASMA MEMBRANE as a very thin structure composed of a bilayer (double layer) of lipid molecules with protein molecules “plugged into” or dispersed in it.
- The proteins, many of which float in the fluid lipid bilayer, form a constantly changing mosaic pattern
Membrane Lipids
Constructed largely of phospholipids and smaller amounts of cholesterol
Phospholipids
- Membrane lipid
- the polar hydrophilic heads (includes phosphate group) of phospholipids are attracted to water. they lie on the inner and outer surfaces of the membrane
-the nonpolar hydrophobic tails (fatty acids) of phospholipids avoid water and line up in the center of the membrane
Cholesterol
- Membrane lipid
- Makes up 20% of membrane lipid
- Has a polar region (hydroxyl group) and a nonpolar region (its fused ring system)
- Wedges its platelike hydrocarbon rings between the phospholipid tails, which stiffens the membrane
- Increases membrane stability and fluidity
Membrane Proteins
-Proteins make up half of the plasma membrane by mass and are responsible for most of the specialized membrane functions Membrane proteins perform many tasks: -Transport -Receptors for signal transduction -enzymatic activity -cell-cell recognition -attachment to the cytoskeleton and extracellular matrix (ECM) -Cell to cell joining slide 12 in ppw
Lipid Rafts
- 20% of the outer membrane surface
- Contain phospholipids, sphingolipids, and cholesterol
- May function as stable platforms for cell-signaling molecules or receptors
Membrane Proteins- TRANSPORT
- A protein that spans the membrane may provide a hydrophilic channel across the membrane that is selective for a particular solute
- Some transport proteins hydrolyze ATP as an energy source to actively pump substances across the membrane
Membrane Proteins-Receptors for signal transduction
- A membrane protein exposed to the outside of the cell may have a binding site that fits the shape of a specific chemical messenger, such as a hormone
- when bound, the chemical messenger may cause a change in shape in the protein that initiates a chain of chemical reactions in the cell
Membrane Proteins-enzymatic activity
A membrane protein may be an enzyme with its active site exposed to substances in the adjacent solution
Membrane Proteins-cell-cell recognition
some glycoproteins (proteins bonded to short chains of sugars which help to make up the glycocalyx) serve as ID tags that are specifically recognized by other cells
Membrane Proteins-attachment to the cytoskeleton and extracellular matrix (ECM)
elements of the cytoskeleton (cell’s internal framework) and the extracellular matrix (fibers and other substances outside the cell) may anchor to membrane proteins
-helps maintain cell shape, fixes the location of certain membrane proteins, and plays a role in cell movement
Membrane Proteins-Cell to cell joining
membrane proteins of adjacent cells may be hooked tg in various kinds of intercellular junctions
-some membrane proteins (cell adhesion molecules or CAMS) of this group provide temporary binding sites that guide cell migration and other cell-to-cell interactions
Integral Proteins (membrane protein)
- firmly inserted into the lipid bilayer
- most are transmembrane proteins that span the entire membrane and protrude on both sides
- have both hydrophobic and hydrophilic regions
- some transmembrane proteins are involved in transport, form channels, or pores
- Functions as transport proteins (channels & carriers), enzymes or receptors
- small water soluble molecules or ions can move through these pores bypassing the lipid part of the membrane
- others act as carriers that bind to a substance and then moves it through the membrane
- some are enzymes
- others are receptors for hormones or other chemical messengers and relay messages to the cell interior– a process known as signal transduction
Peripheral Proteins (membrane protein)
- not embedded in lipid bilayer
- they either attach loosely to integral proteins or have a hydrophobic region that anchors them into the membrane
- includes a network of filaments that helps support the membrane from its cytoplasmic side
- some peripheral proteins are enzymes
- others are motor proteins involved in mechanical functions such as changing cell shape during cell division and muscle cell contraction
- Functions as enzymes, motor proteins, cell to cell links, provide support on intracellular surface & form part of glycocalyx
Glycolipids and glycoproteins
- Lipids and proteins with sugars attached
- glycolipids have 2 fatty acid tails (like phospholipids) but a carb replaces the phosphate head group
Glycocalyx
- “sugar covering”
- consists of the fuzzy, sticky, carbohydrate-rich area at the cell surface created by the sugars of glycoproteins and glycolipids
- cells are sugar-coated like breakfast cereal
- every cell type has a different pattern of sugars in its glycocalyx, the glycocalyx provides identity molecules - highly specific biological markers by which approaching cells recognize each other
- ex: immune system cells use these markers to determine which cells belong in the body and which are foreign
a carb
Tight Junctions
A series of integral protein molecules in the plasma membranes of adjacent cells fuse tg like a zipper of a ziploc bag.
This forms an impermeable junction that encircles the cell and separates one fluid compartment from another
helps prevent molecules from passing through the extracellular space between adjacent cells and restrict the movements of membrane proteins
ex: keeps digestive enzymes in the stomach
Desmosomes
- serve as anchoring junctions- mechanical couplings scattered like rivets along the sides of adjacent cells to prevent their seperation
- Desmosomes bind neighboring cells together into sheets and also contribute to a continuous internal network of strong fibers that act as “guy-wires”
- guy-wires distribute tension throughout a cellular sheet and reduces the chance of the sheet tearing when it is subjected to pulling forces
- desmosomes are abundant in tissues that are subjected to great mechanical stress such as skin and heart muscle
Gap Junction
- A communicating junction between adjacent cells
- at gap junctions the adjacent plasma membranes are very close , and the cells are connected by hollow cylinders (called connexons) composed of transmembrane proteins.
- different gap junctions are composed of different transmembrane proteins and they determine what can pass through them from one cell to another
- present in electrically excitable tissues such as the heart and smooth muscle
Passive Transport
- no added energy required (uses kinetic energy)
- substances move from high to low concentration (down their concentration gradient)
Active Transport
- Requires added energy (ATP)
- substances can move from low to high concentration (against their concentration gradient)
passive membrane transport processes: diffusion
- simple diffusion
- facilitated diffusion
- osmosis
simple diffusion
- Energy source: Kinetic
- Description: Net movement of molecules down their concentration gradient (from higher to lower)
- Membrane transport protein required?: NO
- Specific and saturable?: NO (passage depends only on small size and lipid solubility)
- examples; lipids, oxygen, carbon dioxide
fat soluble molecules diffuse through the phospholipid bilayer
facilitated diffusion
- Energy source: Kinetic
- Description: Same as simple diffusion, but the diffusing substance is attached to a membrane carrier protein or moves through a channel protein
- Membrane transport protein required?: YES
- Specific and saturable?: YES (specificity depends on shape inside transport protein)
- examples; glucose, Na+, K+
Osmosis
- Energy source: Kinetic
- Description: Diffusion of water through a selectively permeable membrane; can occur directly through the lipid bilayer or via membrane channels (aquaporins)
- Membrane transport protein required?: NO, except for movement through the aquaporins
- Specific and saturable?: NO, except for movement through the aquaporins
- examples; water
Who are the key players of the plasma membrane?
Lipids, carbs, proteins
Phospholipids
- Key player in the plasma membrane (1/3)
- forms the basic structure of the membrane
- hydrophobic tails prevent water-soluble substances from crossing, forming a boundary
Cholesterol:
-stiffens membrane further decreases water solubility of membrane
Proteins
- Key player in the plasma membrane (2/3)
- determines what functions the membrane can perform
- many roles: transport, communication (acting as receptors for signal molecules, and joining cells to each other and to the extracellular matrix
Carbohydrates
- Key player in the plasma membrane (3/3)
- act as identity molecules
- allows cells to recognize “who is who” , e.g during cell development so the cell sort themselves into tissues and organs
- allows immune cells to recognize our own
-are found on the outer surface of the membrane, like the sugar coating on breakfast cereal. this forms a coating called glycocalyx
Speed of diffusion is influenced by 3 factors:
- concentration
- molecular size (smaller molecules diffuse more rapidly)
- Temperature (higher temp, more kinetic energy, increases the speed of molecular movement.
What determines whether a given substance can cross the plasma membrane?
- Lipid solubility- the more lipid soluble, the more readily it will diffuse across
- Size- the smaller the molecule the more readily it will diffuse
A molecule can still cross the barrier if they lack these two things through the use of a carrier molecule such as an ion channel or transport protein
The unassisted diffusion of lipid-soluble or very small particles is called simple diffusion
true
Such substances are usually small non polar molecules that readily dissolve in lipids.
-These include gases such as oxygen and carbon dioxide, steroid hormones, and fatty acids
Assisted diffusion is known as facilitated diffusion
true
Carrier mediated facilitated diffusion
via protein carrier specific for one molecule
- binding of solute causes transport protein to change shape so that it first envelopes a molecule on one side of the plasma membrane, and then releases it on the other side allowing it to bypass the nonpolar regions of the membrane
- lipid-insoluble solutes such as sugars and amino acids can pass through this way
glucose moves down its concentration gradient (high to low), just as in simple diffusion. glucose is higher in concentration in the blood than in the cells. so glucose transport within the body is typically unidirectional, into the cells
-limited by the amount of protein carriers available. if all are being used it said to be saturated
Channel mediated facilitated diffusion through a channel protein
mostly ions selected on basis of size and charge
- Leakage channels: are always open and simply allow ions and water to move according to concentration gradients
- Gated channels: are controlled (open or closed), usually by chemical or electrical signals
- molecules move down the concentration gradient
- channels can become saturated and they tend to be specific
hydrostatic pressure
the backpressure exerted by water against the cell wall
osmotic pressure
the tendency of water to move into the cell by osmosis
-the higher the amount of non diffusible or nonpenetrating solutes in a cell, the higher the osmotic pressure and the greater the hydrostatic pressure must be to resist further net water entry
Tonicity
the ability of a solution to change the shape (or plasma membrane tension) of cells by altering the cells’ internal water volume
Isotonic Solutions
- “The same tonicity”
- cells exposed to isotonic solutions retain their normal shape and exhibit no net loss or gain of water.