Lecture 6 Flashcards
All cells (prokaryotic or eukaryotic) have …
- Surrounded by a selective barrier: plasma membrane
- Filled with cytoplasm
- Have a cytoskeleton
- Have ribosomes (they are not organelles)
- Contain chromosome(s): DNA + protein
Cytoplasm
everything inside the cell, except for the nucleus.
Does not include the plasma membrane.
The cytoplasm is where the chemical reactions of a cell take place.
Cytosol
fluid part of the cytoplasm
PROKARYOTIC organisms
characteristics
No organelles: ex DNA not in a nucleus
Genomic DNA: (1) circular chromosome
All are unicellular (single-celled), but some can stick together to form colonies
EUKARYOTIC organisms
Organelles, including a nucleus, are present
Genomic DNA: multiple linear chromosomes
Some are unicellular, others are multicellular
2 types of cell membranes
Separation between internal & external environments must exist: Allows the internal environment to be different from the external environment.
1) The cell membrane that forms the boundary between the inside & outside of the cell is called a plasma membrane.
2) The cell membranes that are part of organelles are simply called cell membranes
Where are the cell membranes for prokaryotes and eukaryotes
Prokaryotes: only the plasma membrane.
Eukaryotes: plasma membrane & as part of organelles
Fluid Mosaic Model
Liquid at body temp.: like olive oil
Mostly phospholipid
Also contains sterol (lipid) & some carbs
Proteins, lipids can move within the membrane
Microvilli
Microvilli: cell extensions that contain cytoskeleton, fluid, and enzymes for digestion.
Covered by plasma membrane
Function: Increase the surface area of the cell exposed to the lumen to enhance absorption and secretion
Functions of plasma membrane
2-5 require proteins
- Keeps each cell intact: boundary
- Cell-to-cell contact: needed to form tissues
- Cell-to-cell recognition: one cell recognizes another based on proteins present on the cell surface (ex immune response)
- Cell signaling (communication): one cell releases chemicals that bind to receptors in the plasma membrane of another cell. Ex receptors for hormones, neurotransmitters
- Movement of molecules into/out of cell
Selectively permeable
Plasma membrane
boundary between inside & outside of ALL cells
Selectively permeable: how the membrane “decides”
Chemical properties determine what enters directly:
Small molecules pass through.
Membrane mostly lipid, so lipid-soluble molecules can pass.
Transporters are specialized proteins: channels or carriers are present for certain but not all molecules.
Bulk transport mechanisms: endocytosis, exocytosis
Everything else is excluded
Exchange with the environment
Into cell
Nutrients: sugars, aa, fa, O2, ions, vitamins…
Some hormones
Out of cell
Metabolic wastes like CO2
Hormones, enzymes, neurotransmitters, ions…
Molecules are continually moving into & out of organelles as well
Functions of The cytoskeleton in eukaryotes
- Mechanical support & maintains cell shape
- Cell motility
Move entire cell (ex wbc) or parts of a cell ex organelles on “train tracks”, plasma membrane during phagocytosis) - Anchor organelles & enzymes
- Cell division
Cell extensions
Eukaryotic flagella, cilia, & microvilli are extensions of the plasma membrane (covered by the plasma membrane).
Contain proteins of the cytoskeleton & other proteins (ex transport proteins, enzymes).
Microvilli: folds of plasma membrane that serve to increase surface area of cell: for absorption or secretion.
Movement:
Cilia & Flagella contain complex set of proteins that cause the cilia & flagella to move
Cilia: move molecules over surface, ex in respiratory tract, or move entire cell, ex paramecium
Flagella: move entire cell, less numerous than cilia.
Cell wall in
All fungi (most multicellular, some unicellular) All plants (multicellular) Some protists (some unicellular, others multicellular) Most bacteria (unicellular)
In multicellular or colonial organisms (whether they have a cell wall or not):
Intercellular junctions
Extracellular matrix (molecules that provide support & influence gene expression) & fluid
Cell walls functions
- Protects the cell
- Maintains its shape
- Prevents excessive uptake of water
Between animal cells
Intercellular junctions:
Adhere
Communicate
Cell adhesion molecules-some act like Velcro, while others form a more permanent bond
Between plant cells
Plasmodesmata are tiny channels that lie between the cell walls of plant cells. They allow molecules, nutrients, and water to move between cells – known as intercellular communication
Extracellular matrix
Extracellular matrix (ECM)=
Fluids +
Nutrients (Proteins, minerals…) +
Signaling molecules
Provide support, nutrients, & can affect gene expression
