Cell Part 1 Flashcards
3 basic components of cells
Genetic material
Plasma membrane
Cytoplasm
Genetic material of prokaryotes is found in the
Nucleoid region
Genetic material of eukaryotes is found in the
Nucleus
Plasma membrane consists of
Lipids
Proteins
Carbohydrates
Lipids
Phospholipids
Cholesterol
= major constituents of membranes
Weighs how many percent
Proteins
50%
= proteins that are are incorporated directly within the lipid bilayer
Transmembrane or Integral
= proteins that are bound to one of the two membrane surfaces, particularly on the cytoplasmic side
Peripheral
The ___________ that envelops every eukaryotic cell consists of phospholipids, cholesterol, and proteins, with oligosaccharide chains covalently linked to many of the phospholipids and proteins.
plasma membrane (cell membrane or plasmalemma)
Functions as a selective barrier regulating the passage of materials into and out of the cell and facilitating the transport of specific molecules.
plasma membrane
also perform a number of specific recognition and signaling functions, playing a key role in the interactions of the cell with its environment
Membrane proteins
Functions of Plasma Membrane
Physical barrier
Selective permeability
Electrochemical gradients
Communication
Polar head group
Hydrophilic
Nonpolar tail (fatty acid chain)
Hydrophobic
= carbohydrate attached to a lipid
Glycolipid
= carbohydrate attached to a protein
Glycoprotein
True or False | phospholipids are amphipathic
True
True or False | Phospholipids are most stable when organized into a double layer (bilayer) with the hydrophobic fatty acid chains located in a middle region away from water and the hydrophilic polar head groups contacting the water
True
Is the amount of membrane cholesterol equal to the amount of the phospholipids?
• Yes. Membrane cholesterol is present in about the same amount as phospholipid.
- contain high concentration of cholesterol and saturated FA (fatty acid)
Lipid rafts
The __________ model of membrane structure emphasizes that the phospholipid bilayer of a membrane also contains proteins inserted in it or associated with its surface (peripheral proteins) and that many of these proteins move within the fluid lipid phase.
fluid mosaic model
Examples of integral proteins
Channels, transporters, pumps, receptors
= transports small, nonpolar molecules directly through the lipid bilayer. Lipophilic (fat-soluble) molecules diffuse through membranes readily, water very slowly.
Simple Diffusion - Passive
= are multipass proteins forming transmembrane pores through which ions or small molecules pass selectively. Cells open and close specific _____ for Na+, K+, Ca2+, and other ions in response to various physiological stimuli.
Channels
Water molecules usually cross the plasma membrane through channel proteins called______.
aquaporins
= are transmembrane proteins that bind small molecules and translocate them across the membrane via conformational changes
Carriers
Movement of substances down a concentration gradient due to the kinetic energy of the substance; no expenditure of cellular energy is required; continues until equilibrium is reached (if unopposed)
PASSIVE PROCESSES
Unassisted net movement of small. Nonpolar substances down the concentration gradient across a selectively permeable membrane
Exchange of oxygen and carbon dioxide between blood and body tissues
Simple diffusion
Movement of ions and small, polar molecules down their concentration gradient; assisted across a selectively permeable membrane by a transport
protein
Facilitated diffusion
Movement of ion down its concentration gradient through a protein channel
Na* moves through Na* channel into cell
Channel-mediated
Movement of small, polar molecule down its concentration gradient by a carrier protein
Transport of glucose into cells by glucose carrier
Carrier-mediated
Diffusion of water across a selectively permeable membrane
Direction is determined by relative solute concentrations: continues until equilibrium is reached
Solutes in blood in svstemic capillaries “pulls” fluid
from interstitial space back into the blood
Osmosis
= are enzymes engaged in active transport, utilizing energy from the hydrolysis of adenosine triphosphate (ATP) to move ions and other solutes across membranes, against often steep concentration gradients.
Membrane pumps
Because they consume ATP pumps, they are often referred to as____.
ATPases
Movement of substances requires expenditure of cellular energy
Active processes
Transport of ions or small molecules across the membrane against a concentration gradient by
transmembrane protein pumps
Active transport
Movement or substance up its concentration gradient: powered directly by ATP
Ca- pumos transport Ca- out of the cell Na/K
Pump moves Na out of the cell and K* into the cell
Primary
Movement of a substance up its concentration gradient powered by harnessing the movement of a second substance (eq, Na*) down its concentration gradient
Secondary
Movement of substance up its concentration
gradient in the same direction as Na+
Symport
Movement of substance up its concentration gradient in the opposite airection from Na’
Antiport
each bind a single solute and transport it across the lipid bilayer.
Carrier proteins
= Movement of substance up its concentration gradient; powered directly by ATP
Primary Active Transport
Transport by vesicles
Endocytosis
Exocytosis
= a general process wherein macromolecules normally enter cells by being enclosed within folds of plasma membrane which fuse and pinch off internally as spherical cytoplasmic vesicles (or vacuoles).
ENDOCYTOSIS
3 major types of endocytosis
Phagocytosis
Pinocytosis
Receptor mediated endocytosis
“Cell eating”
the ingestion of particles such as bacteria or dead cell remnants.
Phagocytosis
Ex: Blood derived cells, such as macrophages and neutrophils
Involves the extension from the cell of surface folds or pseudopodia which engulf particles such as bacteria, and then internalize this material into a cytoplasmic vacuole or phagosome.
Phagocytosis
= an intracellular vacuole where fusion of the membranous folds encloses the bacterium in; merges with a lysosome for degradation of its contents
Phagosome
“Cell drinking”
The cell membrane forms similar folds or invaginates (dimples inward) to create a pit containing a drop of extracellular fluid.
Pinocytosis
The pit pinches off inside the cell when the cell membrane fuses and forms a pinocytotic vesicle containing the fluid.
Pinocytosis
= pinocytosis - the latter process; accomplishes bulk transfer of dissolved substances across the cell.
Transcytosis
Includes membrane proteins called receptors that bind specific molecules (ligands).
Receptors for many substances, such as low-density lipoproteins and protein hormones, are integral membrane proteins at the cell surface.
When many such receptors are bound by their ligands, they aggregate in one membrane region, which then invaginates and pinches off to create a vesicle or endosome containing both the receptors and the bound ligands.
Receptor-mediated endocytosis
= a process that involves the movement of large molecules from inside to outside the cell
EXOCYTOSIS
Vesicle formed or lost as material is brought into a cell or released from a cell
Vesicular transport
Bulk movement of substance out of the cell by fusion of secretory vesicles with the plasma membrane
Exocytosis
Bulk movement of substances into the cell by vesicles forming at the plasma membrane
Endocytosis
Type of endocytosis in which vesicles are formed as particulate materials external to the cell are engulfed by pseudopodia
Phagocytosis
Type of endocytosis in which vesicles are formed as interstitial fluid is taken up by the cell
Pinocytosis
Type of endocytosis in which plasma membrane receptors first bind specific substances; receptor and bound substance then taken up by the cell
Receptor mediated Endocytosis
SIGNAL RECEPTION & TRANSDUCTION: DIRECT CONTACT
Gap Junctions
Juxtacrine Signaling
Where are Gap Junctions located?
found in the lateral part
CATEGORIES OF SIGNALING PROCESSES:
Endocrine Signaling
Paracrine Signaling
Synaptic Signaling
Autocrine Signaling
Juxtacrine Signaling
The signal molecules (here called hormones) are carried in the blood from their sources to target cells throughout the body
Endocrine Signaling
The chemical ligand diffuses in extracellular fluid but is rapidly metabolized so that its effect is only local on target cells near its source
Paracrine Signaling
A special kind of paracrine interaction
Neurotransmitters act on adjacent cells through special contact areas called synapses
Synaptic Signaling
Signals bind receptors on the same cells that produced the messenger molecule
Autocrine Signaling
Important in early embryonic tissue interactions, the signaling molecules are cell membrane-bound proteins, which bind surface receptors of the target cell when the two cells make direct physical contact.
Ligand is attached to the cell for cell-cell interaction
Juxtacrine Signaling
3 IMPORTANT FUNCTIONAL CLASSES OF RECEPTORS
Channel-linked Receptors
Enzymatic Receptors
G-protein–Coupled receptors
= open associated channels upon ligand binding to promote transfer of molecules or ions across the membrane
bind ligands such as neurotransmitters and open to allow influx of specific ions.
Channel-linked Receptors
= ligand binding induces catalytic activity in associated peripheral proteins.
Activates enzymes
usually protein kinases that are activated to phosphorylate (and usually activate) other proteins upon ligand binding.
Enzymatic Receptors
= upon ligand binding stimulate associated G-proteins which then bind the guanine nucleotide GTP and are released to activate other cytoplasmic proteins
bind ligand, changing the conformation of its G-protein subunit, allowing it to bind GTP, and activating and releasing this protein to in turn activate other proteins such as ion channels and adenyl cyclase.
G-protein–Coupled receptors
