Cell Membrane Function

Cell Structure and Function

• The cell is the fundamental structural and functional unit of all living organisms.
• Cells are diverse, ranging from filamentous fungi and bacteria to blood cells, radiolarians, protozoa, gametes, intestinal cells, xylem, and retinal neurons.

History of Cell Biology

• Genetics, biological chemistry, and cytology have merged to form cell biology basis of all biology and applied biologies.
• Cellular biology underlies various fields, including agriculture, environmental sciences, nutrition, and medicine.

Cell Theory

• All organisms are composed of one or more cells.
• The cell is the basic unit of life.
• New cells arise from pre-existing cells.
• Before cell theory, spontaneous generation from rotting organic matter was a common belief.

Cell Behaviors

• Cell behavior is key to biology, encompassing cell-cell communication, shape changes, movement, proliferation, and cell death (apoptosis).
• Resolution in microscopy is the ability to distinguish closely spaced objects.
• Microscopy has been crucial for advancing cell biology.
• Light Microscopy (LM) resolving power is 200-350 nm.
• Various LM techniques exist, including bright field, fluorescence, phase contrast, differential interference contrast, and confocal microscopy.
• Transmission Electron Microscopy (TEM) has a resolving power of 0.1-0.2 nm.
• Scanning electron microscopy and transmission electron microscopy are types of EM.

Model Organisms

• Specific organisms are selected for intense study; examples include E. coli, S. cerevisiae, Drosophila melanogaster, C. elegans, Mus musculus, and Arabidopsis.

Hierarchical Nature of Cellular Structure

• Small organic molecules are the first level of biological structure.
• Macromolecules form the second tier.
• Progression continues through supramolecular structures.
• Afterwards: organelles and subcellular structures.
• Lastly, the cell.

Chemistry of the Cell

• Organic chemistry initially focused on biological compounds.
• Now, it is distinct due to synthesis of non-biological compounds.
• Biological chemistry (biochemistry) is a part of modern cell biology.
• Carbon's valence of four enables it to form stable molecules and four chemical bonds.
• Carbon readily forms molecules with hydrogen, oxygen, and nitrogen, and can create double and triple bonds.
• Tetrahedral structure causes carbon atoms with four different bonded atoms or groups to have stereoisomers.

Water

• Universal solvent in biology, water molecules are polar causing unequal electron/charge distribution.
• Due to polarity, water molecules are cohesive and form hydrogen bonds.
• High surface tension, boiling point, and heat of vaporization stem from water's properties.
• Water efficiently dissolves sodium chloride and is an excellent solvent.
• Hydrophilic substances dissolve in water, while hydrophobic ones do not.

Selectively Permeable Membranes

• Membranes act as barriers to control cell content.
• Membrane lipids and proteins are amphipathic, having both hydrophilic and hydrophobic regions.
• Amphipathic phospholipids form the lipid bilayer, approximately (3 to 4 nm X 2) 7 to 8 nm thick.
• Membrane proteins are embedded and aid in various processes.
• Membranes are semi-permeable.

Synthesis by Polymerization

• Biological molecules are often linear polymers made of simple monomers; like proteins that are amino acids, DNA & that is RNA nucleotides and starch, glycogen and cellulose being simple sugars.
• Lipids are complex polymers.

Self-Assembly

• Many biological compounds, proteins especially, can undergo "self-assembly".
• Denatured proteins can return to their native form through renaturation, which goes through spontaneous protein/peptide folding.
• Molecular chaperones are proteins that temporarily bind to new or unfolded proteins to ensure proper folding.
• Weak non-covalent interactions are important in the formation of macromolecules.

Macromolecules of the Cell

• Macromolecules consist of approximately 30 small molecules.
• Proteins consist of amino acids and have about 60 amino acids in a cell.
• 20 amino acids are used in protein synthesis.
• Amino acids are represented with 1 and 3 letter codes with abbreviations.
• Amino acid subunits can be modified after proteins/peptides are created.
• Amino acids have a central alpha-carbon, an amino group, a carboxyl group, and an R group.
• Different R groups exist for each amino acid; hydrophobic versus hydrophilic.
• Proteins and peptides form linear amino acid polymers.
• Synthesis occurs in an "amino (N) to carboxyl (C)" direction.
• The N-terminal end begins while the C-terminal end concludes.
• Peptide bonds form during polymerization.
• Stabilization occurs through disulfide, hydrogen, and ionic bonds, and Van der Waals/hydrophobic interactions. Protein structures depend on amino acid sequence and interactions among the acids
• There are four levels of protein organization: primary, secondary, tertiary, and quaternary, building upon previous levels

Nucleic Acids

• Polymers of nucleotides.
• DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) differ in the 5’ carbon sugar part of the nucleotide (deoxyribose versus ribose).
• DNA stores "genetic information", while RNA uses the information.
• A nucleotide includes: nitrogenous base (purines or pyrimidines).
• Nucleotides also include: 5 prime carbon sugar and a phosphate group
• Nucleic acids are linearly arranged with nucleotides.
• Direction: made in "5 prime to 3 prime" direction.
• Linearly, "5 prime" begins and "3 prime" ends.
• "3 prime", "5 prime" phosphodiester bridges join nucleic acids.
• DNA has double helix structure.
• DNA held together by hydrogen bonds between A-T and G-C pairs on opposite strands.

Polysaccharides

• Polymers of simple sugars like glucose.
• Polysaccharides store and provide structure like starch & glycogen, and that is cellulose

Lipids

• Polymers of many monomers, like fatty acids.
• Heterogeneous group of hydrophobic macromolecules
• Energy store, membrane structure and specific biological functions are served.

Prokaryotes and Eukaryotes

• Great diversity exists between prokaryotes and eukaryotes.
• Prokaryotes are bacteria.
• Prokaryotes have: plasma membrane and circular DNA.
• Also have: ribosomes (70S) and go through binary fission.
• Eukaryotes are animal and plant cells
• Eukaryotes have an array that prokaryotes do not: plasma membrane and internal membrane-bound compartments / organelles
• Eukaryotes have: DNA plus proteins and linear chromosomes
• Also have: histones larger ribosomes (80S); mitosis & meiosis and cytoskeleton plus endocytosis & exocytosis

Evolution of the Eukaryotic Cell

• Encompasses the origin of chloroplasts and mitochondria.
• Notably, mitochondria and chloroplasts are "semi-autonomous organelles".

Theory 1) Autogenous

• Eukaryotic cells evolved from a single prokaryote ancestor.
• This occurs through compartmentalization of functions from invaginations of the prokaryotic plasma membrane, which forms organelles enclosed by a membrane
• The endoplasmic reticulum (ER), Golgi apparatus, and the the nuclear membrane are enclosed by a single membrane

Theory 2) Serial Endosymbiotic(SET)

• Mitochondria and chloroplasts evolved by compartmentalizing plasmids within vesicles from the plasma membrane.
• Prokaryotic cells engulf aerobic bacteria.
• Instead of digesting, symbionts aid the host by removing O2 and producing ATP.
• Growing interdependence transforms the bacterium becomes the mitochondrion.
• Some cells engulf blue-green algae, forming chloroplasts.

Evidence for SET and the Ancestry of Mitochondria and Chloroplasts

• Same size, similar appearance, and double membrane characteristics.
• Binary fission.
• Encompasses: common enzymes for respiration and photosynthesis.
• The genetic material used also influences the cell: Single circular DNA molecule with no histone proteins, few proteins, and continuous S phase.
• Common gene sequences like: rDNA, tDNA
• Similarity in ribosomes to eukaryotes also present, 70S ribosomes in organelles and prokaryotes (eukaryotes have 80S in the cytoplasm)
• Sensitive to a range of antibiotics and start codons used

Cell Structures and Organelles

• Cell Membranes: Define cell boundaries and selectively permeable internal compartments.
• Made of lipids and proteins
• Around ~8 nm in diameter
• Extracellular boundaries have other forms besides membranes: Contain plant cell walls, fungal cell walls, and the animal extracellular matrix (ECM).
• Ribosomes(30 nm) are sites of protein synthesis and translation.
• Free or associated with membranes (Rough endoplasmic reticulum: rER
• Nucleus: Compartmentalizes genetic material
• Site of DNA synthesis (S) & RNA synthesis (transcription).
• Enclosed by a double membrane with nuclear pores and consisting of chromatin and nucleolus.
• Endomembrane System has other elements as well: ER, Golgi apparatus & Vesicles
• Related Structurally and Functionally
• Responsible for: Synthesis as well as secretion
• Involved: Protein, Carb and Lipids

Organelles that Assist the Endomembrane System

• Lysosomes: Recycle material with hydrolases.
• Peroxisomes: Assist in processes of breaking down fat.
• Generate with hydrogen peroxide as a by-product

Energy Flow

• Chloroplasts: Photosynthesis occurs in these locations, used to create energy-rich fuel from sunlight
• Mitochondria: Creates ATP, fuel is made here
• Creates: ACR, Heat

Cytoskeleton

• 3D protein-based filament arrays.
• Microtubules, microfilaments, and intermediate filaments are the components.
• Cell shape, movement, signaling, endocytosis, and mitosis.

Bioenergetics: The Flow of Energy in the Cell

• Capacity to obtain, store and use energy.

Energy Requires 6 Processes:

• Synthetic work
• Mechanical work
• Concentration work
• Electrical work
• Heat generation
• Bioluminescence

Energy Source

• Phototrophs (light-feeders) or chemotrophs (chemical feeders)
• Oxidation and reduction, Energy flows constantly in Earth.
• Matter being material of Earth.

Law

• Energy conserved
• Reactions directed
• Entropy and potential energy

Steady

• Close to maintaining the current state.
• Steady state input for large energies.

Catalyst of Life

• Enzymes used for catalytic rxns without enzymes.

Stable

• Potential to get over energy to increase involved.

Binding Enzymes as Biological Catalysts

• Enzymes: Proteins that catalyze reactions.
• Active sites: Regions where substrates bind and catalysis occurs, exemplified by lysozyme with high substrate specificity.
• Enzymes Temperature Affects: Dependent upon temperature, pH, and presence of inhibitors/activators.
• Main Enzymes: These include oxidoreductases, transferases, hydrolases, lyases, isomerases, and ligases

Changes

• Molecule change like the enzyme change and the binding.
• Common like electron and the bond for reactions.
• Catalytic cycles reaction of an change.

Enzymes Display

• Michaelis-Menten Kinetics.
• Display and Regulated by the non-competitive

Part of Enzymes Reactions: Ribozymes

• Ribozymes are RNA,containing biology catalysts

Functions of Cell Membranes

• Defined boundaries barrier
• Unique functions

Regulations of Boundaries Functions:

• Solute transported
• Signal is detected for transport
• Communicate of cells

Membranes Structure contains:

• Lipid has bilayer
• Integral of protein

Model and Structure is Mosaic

• Fluid- Like mosaic is a universial model of cells and membranes-Lipidis are regulated and their structure may regulated by:
• The two proteins are functions and the fluidity are limited.
• Membranes are symmetrical

Main Classes of Membranes

• Three has three membrane is on a cell
• most prominently lipids
• polar- head of the lipid for fatty acids

Types of Sterols for Main Classes

• Rings- cholesterol.
• behave
• Little across is of the layer
• fluidity- rotation and lateral diffusion.
• Function membrane is effected by:
• Length with fatty acids
• the number of double functions
• Moderated is both direction, with up to 50%
• regulated by changes with number double.

Fluid and Freeze Microcopy:

• shows they floating layer or and floating layer is on a cell

Method membrane

• Have be removed to.

Transport Cell Across

• Some transport has diverse and is employed by diverse.
• Hyrdphobic layer and substances across- Important barrire
• allow in cell

Substances Across Cell include:

1. Simple diffusion : via lipins
2. Facilitated diffusion: proteins
3. Active transported : transport from the gradient

Non Selective

• Non polar in the cell membrane Facilitated Diffusion in Membranes:
  • Proteins for some in the cell

Protiens and Cell Membranes

• Very for certain
• Carrier are transported .
• Transmitter: Proteins in Glucose.
• Glucose - 5. 0 mm vs limited mm.

Transmiter in Exchange

• Anion the protein

Proteins channels

• channels for a few things.
• Regulated by : Stretching and Ligand that is bounded
• Indirect with ATP .
• Gradient substance for the cells constant
• the pump P Type events
• many ATp types exist.

Transports that are not in Active: Co and Port:

• Coupled gradient
• The Sympoter in Sodium = driven gradient on the intestine
• Protons light that drives protons

Energry Metabolism

• Energy Flow,Glycolysi and Resporation.