Physio Exam 1 (copy)

Forms of cell attachments

Forms of cell attachments

transient and stable

Transient attachment

refers to temporary adhesion between immune system cells, guiding white blood cells to areas of tissue damage or inflammation. It involves weak bonds and interactions.

Stable cell attachment

involves long-lasting adhesion between cells or between cells and the extracellular matrix. It forms strong bonds that firmly hold cells together.

Types of cell attachments based on binding properties

heterophilic and homophilic

Heterophilic binding

this occurs when cells bind to other cells of a different type

Homophilic binding

this happens when cells bind to other cells of the same type

Different types of intercellular bridges

anchoring junctions, GAP junctions, and tight junctions

Anchoring junctions

include desmosomes, hemidesmosomes, and adherens junctions, help cells attach to each other and provide mechanical strength.

GAP junctions function

for direct chemical communication between neighboring cells' cytoplasm without contacting the extracellular fluid. They coordinate heart muscle contraction, facilitate brain signal transfers, and promote cell differentiation and proliferation in retinal/skin cells.

Tight junctions

These junctions form a barrier between cells, preventing the passage of molecules and ions, and helping to maintain tissue integrity

Intermediate filaments

a type of cytoskeletal structure that play a role in providing mechanical support and stability to cells. They indirectly contribute to cell attachment by connecting and interacting with other cell junctions.

Desmosomes

cell junctions that connect adjacent cells using intermediate filaments and Cadherin proteins. They provide strong cell-to-cell adhesion through homophilic interactions.

Hemidesmosomes

anchor cells to actin filaments, other cells, and the extracellular matrix. They come in different shapes and sizes, connecting cells as streaks, spots, or bands.

Band-type hemidesmosomes

encircle the cell with actin filaments

Spot-like hemidesmosomes

also known as focal adhesions and primarily attach to the ECM.

Building blocks of GAP junctions

Connexins are the proteins that form connexons. Connexons act as channels, allowing the passage of molecules between adjacent cells. The size and polarity of connexons can vary depending on the specific connexin proteins involved.

Tight junctions

act as barriers, controlling the passage of water and solutes between adjacent cells. They selectively regulate solute movement based on size, polarity, charge, and pH. They prevent the free flow of substances and maintain tissue integrity.

Molecules that are responsible for forming cell junctions

selectins, cadherins, integrins, and immunoglobulin superfamily

Selectins

involved in cell adhesion and play a crucial role in immune responses and inflammation. They mediate the initial interaction between immune cells and endothelial cells during inflammation.

Cadherins

are responsible for cell-cell adhesion and maintaining tissue integrity. They are essential for the formation and stability of adherens junctions

Integrins

play a role in cell-matrix adhesion, connecting cells to the ECM. They are involved in cell migration, signaling, and tissue development. Integrins are important components cell-matrix junctions.

Immunoglobulin superfamily

This diverse group of molecules plays a role in various cell-cell interactions, including immune responses and neuronal development.

Cytoplasmic components

organelles, cytoskeleton/microfilaments, nucleus, vacuoles/vesicles, and dissolved substances

The endoplasmic reticulum

a network of round or tubular structures called cisternae. It is connected to the nuclear membrane and is the largest membrane-bound component in the cell.

Cell theory

all living matter, from the simplest of unicellular organism to very complex higher plant and animals, is composed of smallest functional units called cells and that each cell can act independently, reproduce itself but also functions as an integral part of the organism

Major types of cells

prokaryotic and eukaryotic

General cell structure a biologic protoplasm that has two major components

the nucleoplasm and cytoplasm. These structures determine cellular dysfunctions

Prokaryotic cells

lack of a nuclear envelop. Generally smaller and simpler than eukaryotic cell with less complex genomes. Do not contain cytoplasmic organelles or a cytoskeleton.

Prokaryotic cells examples

archaebacteria and eubacteria

Eukaryotic cells

have genetic information in the nucleus, organized organelles, a cytoskeleton, large cell volume, complex protein transport, and are usually found in multicellular organisms.

The plasma membrane

the outermost covering of cells. It consists of a trilaminar lipid bilayer with hydrophilic outer and inner layers and a hydrophobic core.

Cell membrane composition

55% proteins, 25% phospholipids, 13% cholesterol, 4% lipids, and 3% carbohydrates

Intracellular fluid

fluid within the cell

Extracellular fluid

fluid outside of the cell

Phospholipids

molecules with a structure similar to triglycerides, where one fatty acid is replaced by a phosphate group. The polar head region of the phospholipid are hydrophilic, while the fatty acid tail is hydrophobic

Major type of membrane lipids

Phosphatidylserine, Phosphatidylethanolamine, Phosphatidylcholine, and Sphingomyelin

Minor type of membrane lipids

Phosphatidylinositol

Function of the lipid bilayer

is the backbone of the membrane, forming a stable selective permeability barrier. It also provides membrane plasticity, facilitates the transport of substances, serves as cell receptors, enables cell attachments, and facilitates cell signaling.

Integral membrane proteins

are embedded within the lipid bilayer of the cell membrane. They have two important functions, creating membrane pores and acting as carriers.

Glycoproteins

are proteins with attached carbohydrates. They are located on the outer layer of cells and contribute to determining the cell's vulnerability to pathogens. They carry a negative charge, and higher concentrations provide greater protection to the cell.

Glycolipids

are lipid molecules with attached carbohydrates found on the outer layer of cells. They contribute to the cell's susceptibility to pathogens and provide protection. Higher concentrations of them offer increased cell protection.

Cholesterol

an be found associated with the hydrocarbon chains or phospholipid heads in cell membranes. It plays a crucial role in maintaining the fluidity of the membrane.

Filaments of cytoskeleton

act to suspend the membrane

Types of membrane lipids

steroids, glycolipids, and phospholipids

The outer membrane monolayer is composed of

phosphatidylcholine and sphingomyelin

The inner membrane monolayer is composed

phosphatidylethanolamine and phosphatidylserine

Two of the major translocator proteins involved in the movement of phospholipids form one membrane monolayer to another

scramblases and flippases

Phosphatidylinositol

occurs small amount on the inner membrane monolayer

Two major second messengers produced by phosphatidylinositol

DAG and IP3

Hydrocarbon kinks in membrane lipids

create spaces between the molecules, resulting in increased membrane flexibility even in low tempreatures. Shorter fatty acids have weaker interactions and less packing, while longer fatty acids have stronger interactions and tighter packing.

Types of lipid rafts

cabeola and planar

Lipid rafts

regions in the plasma membrane with high levels of cholesterol and glycosphingolipids. They are thicker and less fluid than the surrounding membrane. Contain proteins involved in cell signaling and play a vital role in cell transduction

Caveolae rafts

are dense lipid raft regions in the cell membrane formed by caveolins. They create small indentations. Cells with more of these structures have faster endocytosis rates

Planar rafts

lipid rafts that do not result in a indent. The proteins associated are flotillins

Main types of membrane proteins

integral proteins and peripheral proteins

Most integral proteins are

glycoproteins, meaning they have carbohydrate molecules attached to them. These glycoproteins are typically exposed on the surface of the cell, extending from the internal monolayer of the membrane.

Nonpolar, hydrophobic amino acids of membrane proteins

Located within the membrane. Include Glycine, Alanine, Valine, Cysteine, Leucine, Isoleucine, Methionine, Phenylalanine, Tryptophan, and Proline. They serve as anchors, helping to embed the protein within the lipid bilayer of the membrane.

Polar, hydrophilic amino acids of membrane proteins

Located on the outer surface. Include Serine, Threonine, Tyrosine, Aspartic acid, and Glutamic acid. They extend into the extracellular space and the cytosol, contributing to the protein's interaction with its environment.

Peripheral proteins

are attached to the surface of the cell membrane and interact with integral proteins. They dissociate when exposed to polar reagents but do not affect the integrity of the phospholipid bilayer. Their stability relies on protein-protein interactions/ionic bonding.

Lateral movement of membrane lipids

Diffusion is restricted by their association with cytoskeleton. Very common

Vertical movement of membrane lipids

very rare

The fluid mosaic model

explains the flexibility and fluidity of the cell membrane. It consists of lipids and proteins in constant motion, resembling a fluid. The lipid bilayer behaves as a two-dimensional fluid, allowing free rotation and lateral movement of molecules.

Carbohydrate functions in membrane

Protection, insulation, provide binding sites for tissue and signaling

Major facilitators of cell attachment within the outer monolayer

Proteoglycans, cell adhesion molecules, glycolipids, and glycoproteins

Membrane lipids and membrane fluidity

Unsaturated fatty acids increase membrane fluidity, while cholesterol has dual effects on membrane rigidity and fluidity. When it interacts with phospholipid head groups and fatty acid chains it enhances rigidity, but when between fatty acid chains it promotes fluidity.

Hydrophilic portions of integral protein

are in the irregular coil configuration.

Hydrophobic portions of integral

are in the helical form and within the membrane.

The rough endoplasmic reticulum

characterized by cisternae, which are flattened, membrane-bound sacs. These cisternae have ribosomes or ribonucleoproteins attached to their cytoplasmic surface. The main functions include protein synthesis, membrane protein insertion, and protein folding.

Exocytosis

a cellular process where intracellular vesicles fuse with the plasma membrane and release their contents outside the cell.

N-linked

This is characterized by the binding of glycan (sugar) to the amino group of asparagines in the RER.

O-linked

This is characterized by the binding of monosaccharide glycan to the hydroxyl group of serine or threonine in the RER, Golgi, cytosol and the nucleus

Types of glycosylation

N-linked, O-linked, Glypiation, C-linked, and Phosphoglycosylation

Glypiation

Gycan core links a phospholipid and a protein

C-linked

Mannose binds to the indole ring of tryptophan.

Phosphoglycosylation

This is where glycan binds to serine via a phosphodiester bond.

Smooth Endoplasmic Reticulum (SER)

lacks ribosomes and is often called agranular reticulum. Its cisternae are tubular and branching. Is involved in the synthesis and transport of membrane lipids, drug biotransformation, iron transport, and the fragmentation of megakaryocytes.

Four functional compartments of the Golgi apparatus have been described

Cis Golgi network (convex end), Medial Golgi stack, Trans Golgi stack, and Trans Golgi network (concave end)

Golgi apparatus function

Membrane redistribution, the concentration of secretory products, and formation of the primary lysosome.

Primary lysosomes

organelles that contain inactive enzymes.

Secondary lysosomes

are formed when primary lysosomes fuse with vesicles or endocytic compartments containing foreign material

The Ubiquitin Proteasome Pathway (UPP)

is a cellular pathway that degrades unwanted or damaged proteins. It involves attaching ubiquitin molecules to target proteins, marking them for degradation by the proteasome.

Ubiquitin enzymes

E1 (activation enzymes), E2, (conjugating enzyme), E3 (ligase)

The proteasome

involved in protein degradation. It consists of the 20S proteasome, which has the degradation activity, and the 19S regulatory particle, which acts as a regulator and transporter. When combined they form the 26S proteasome.

Deubiquitination

is the removal of ubiquitin molecules from proteins. It is carried out by enzymes called deubiquitinases (DUBs) and helps regulate protein function and stability.

Mitochondria

Energy-generating organelles with their own DNA. Proteins required for their assembly are synthesized from nuclear genes and transported into the mitochondria as completed polypeptides. They play a crucial role in cellular energy production.

Structure of mitochondria

has a outer membrane (permeable), an inner membrane (less permeable), and contain enzymes for the citric acid cycle. They have cristae, an intermembrane space, and porins in the outer membrane.

Specialized translocases

contain Tom complex (on the outer membrane), tim complex (on the inner membrane), and chaperones help to facilitate the protein insertion on mitochondrial membrane.

Functions of Mitochondria

Providing the cell’s ATP, control of the level of calcium ions in the cytoplasmic matrix of the cell through the uptake of divalent cations, the initiation of apoptosis, and Beta-oxidation fatty acids

Lysosomes

Are polymorphic, intracellular digestive systems, containing various enzymes, and are optimally active at an acid pH. Produced by the Golgi apparatus.

Lysosomal Dysfunction

Lysosomal storage disease and Gaucher’s disease. Substances do not break down within the lysosomes and inhibits development.

Lysosomal Enzymes

Proteases, Ribonuclease, Deoxyribonuclease, Phosphatase, Glycosidase, Lipase, and Sulphatase.

Functions of the lysosome

Degradation of macromolecules/worn out organelles, removal of excess products, and can have a secretory function.

Phagosomes

formed when cells engulf solid particles through phagocytosis.

Phagolysosome

Result of the fusion between a phagosome and a lysosome, where ingested material undergoes degradation.

Autophagic vacuole

Double-membraned vesicle formed during autophagy to enclose and recycle cellular components.

Peroxisomes

are formed by pinching off from the endoplasmic reticulum. They contain oxidative enzymes like catalase, urate oxidase, and D-amino oxidase. They break down uric acids, amino acids, very-long-chain fatty acids, and branched-chain fatty acids. Are less versatile than lysosomes.

Detoxifies hydrogen peroxide by converting it to water and oxygen.

Peroxisomes is what preforms this action

Actin filaments

enable cell movement, shape changes, and the formation of cell protrusions. They contribute to cell motility and behavior. Can form bundles and networks, held together by actin-binding proteins.

Profilin

A protein that helps assemble actin filaments by promoting the addition of actin building blocks and encouraging their incorporation into growing filaments.

Cofilin

A protein that helps disassemble actin filaments by weakening the interactions between actin building blocks, leading to filament severing and depolymerization.