Chapter 3: Cells: The Living Units Flashcards
Cells
Structural units of all living things
Describe Cell Theory
1) A cell is the BASIC structural and functional UNIT OF LIVING ORGANISMS
2) The ACTIVITY of an organism depends on both the individual and combined activities of its cells
3) BIOCHEMICAL ACTIVITIES of cells are dictated by their SHAPES or forms and the relative number of the sub cellular structures they contain
4) Cells come from OTHER CELLS
Generalized/ Composits Cell
All cells have the same basic parts and some common functions
What are the 3 main parts of a cell?
1) Plasma Membrane
2) Cytoplasm
3) Nucleus
Extracellular materials
Substances contributing to body mass that are found outside the cells
What are the classes of Extracellular materials?
- Body fluids
- Cellular secretions
- Extracellular matrix
Body Fluids (also called extracellular fluids)
Important transport and dissolving media
• Interstitial Fluid
• Blood Plasma
• Cerebrospinal Fluid
Interstitial Fluid
The fluid in tissues that bathes all of our cells and has major and endless roles to play
• Rich, nutritious “soup” (ingredients: amino acids, sugars, fatty acids, regulatory substances and wastes)
• Each cell must extract from this to stay healthy
Cellular Secretion
Substances that aid in digestion and some act as lubricants (saliva, mucus…)
Extracellular Matrix
• Most abundant extracellular material
• Universal Cell “glue”- holds body cells together
1) Body cells are in contact with proteins and polysaccharides (secreted by cells)
2) Molecules self-assemble into organized mesh
Describe the cell membrane
- Lipid Bilayer
* Protein molecules
What are the lipids of the membrane?
1) Phospholipids
2) Glycolipids
3) Cholesterol
Describe the phospholipids
- Polar head is charged and hydrophilic
* Non Polar tail has 2 fatty acid chains and is hydrophobic
Describe the movement of Phospholipids
Move freely side to side
Glycolipids
Lipids with attached sugar groups
- 5% of total membrane lipids
Cholesterol
- 20% of membrane
- Polar region: Hydroxyl
- Non polar: Fused ring system
• Stabilizes membrane
• Decreases mobility of phospholipids and fluids
Membrane Proteins Functions
• Allows cell to communicate w/ environment
- 1/2 plasma mass
• Specialized membrane functions
What are the 2 distinct populations of proteins?
1) Integral
2) Peripheral
Integral Proteins
- Firmly inserted in membrane
- Some protrude one side, Most protrude both (transmembrane proteins)
• Have Hydrophilic and Hydrophobic regions - Can interact with Non-Polar lipid tails and water in/out of cell
Transmembrane Proteins
• Protrude both sides of membrane
- Some transport and provide channels: Water-soluble molecules or ions pass
- Some carry: bind to substance and move through membrane
- Enzymes
- Receptors for hormones
Signal transduction
A process where chemical messengers relay messages to the cell interior
Peripheral Proteins
- Not embedded in membrane
- Attach loosely to integral proteins and can be easily removed
Glycocalyx
Consists of glycoproteins and glycolipids that form a fuzzy, sticky, carbohydrate-rich area at the cell surface
- enriched by glycolipids and glycoproteins secreted by the cell
- *Provides highly specific biological markers by which approaching cells recognize each other; Ex: Sperm recognizes an ovum
What 3 factors act to bind cells together?
1) Glycoproteins in the glyocalyx act an adhesive
2) Wavy contours of the membranes of adjacent cells fit together in a tongue-and-groove fashion
3) Special cell junction form
What 3 junctions are important for factors in securing cells together?
1) Tight Junction
2) Desmosomes
3) Gap Junctions
Tight Junctions
A series of integral protein molecules in the plasma membrane of adjacent cells fuse together, forming an impermeable junction that encircles the cell
- Prevents molecules from passing through the extracellular space between adjacent cells
Desmosomes
Anchoring junctions that bind adjacent cells together act like molecular “Velcro” and also help form an internal tension-reducing network of fibers
- Plaque: is on the face of each plasma membrane
- Cadherins: Protein filaments that hold together adjacent cells that extend from the plaques
- Keratin: the extend from the cytoplasmic side if the plaque to anchor to the plaque on the cells opposite side
Distributes tension throughout a cellular sheet and reduces the chance of tear when under pulling force
- Ex: Skin, Heart muscle
Gap Junctions
Communicating junctions that allow ions and small molecules to pass are particularly important for communication in heart cells and embryonic cells
- adjacent plasma membranes are close connected by hollow cylinders (connezons), which are composed of transmembrane proteins
- Present in electrically excitable tissues where ion passage from cell to cell helps synchronize their electrical activity and contraction
Passive Processes
Substances cross the membrane without any energy input from the cell
Active Processes
The cell provides the metabolic energy (usually ATP) needed to move substances across the membrane
What are the 2 main types of Passive Transport?
1) Diffusion
2) Filtration/ Facilitated
Diffusion
The tendency of molecules or ions to move from an area where they are in higher concentration to an area where they in lower concentration (on the concentration gradient)
Describe the barrier of the plasma membrane?
It allows some substances to pass while excluding others
It allows nutrients to enter to cell, but keeps many undesirable substances out
- Keeps valuable cell proteins in
- Allows waste to exit
What molecules or ions are allowed to through the membrane?
1) Lipid soluble
2) Small enough to pass through membrane channels, or
3) Assisted by a carrier molecule