Unit 3: Biological Membranes & Cell Structure; LM 8-10

3 tenets of cell theory

3 tenets of cell theory

spontaneous generation, biogenesis, unified cell theory

Common features of all cells on Earth

simple molecular systems enclosed by a simple lipid membrane, use glycolysis to break down larger molecules to get energy and biogenic elements,

Conditions on early Earth

extremely hot, evaporating the liquid water into the atmosphere, with no free oxygen, and researchers believe the atmosphere had water vapor, carbon dioxide, carbon monoxide, hydrogen, nitrogen, ammonia, and methane.

1st requirements for life to evolve

Formation of small energy-rich molecules containing carbon and hydrogen

2nd requirements for life to evolve

Formation of self-replicating, information-containing molecules (RNA).

3rd requirements for life to evolve

Development of a membrane to compartmentalize the self-replicating molecules from their surroundings and facilitate metabolic activity.

Endosymbiosis

A symbiotic relationship where one organism lives inside the other

Origins of Eukaryotes

comprise their own domain and have much larger compartmentalized cells with more complex systems

3 Domains of Life

Archaea, the Bacteria, and the Eukarya.

Plant cells

are eukaryotes, multi-celled, and autotrophs

Animal cells

are eukaryotes and autotrophs

Role of organelles

found in all eukaryotic, carry out essential functions that are necessary for the survival of cells(harvesting energy, modifying proteins, getting rid of waste, etc.), some can harness and transform energy, synthesize and modify large macromolecules and digest and secrete macromolecules.

Mitochondria structure

made up of two membranes, outer membrane covers the organelle and the inner membrane folds over many times

Cristae

layered structures in the inner membrane, increase the surface area for reactions to occur

Matrix

The fluid contained in the mitochondria

Nucleus structure and function

main function is to control gene expression and mediate the replication of DNA during the cell cycle, its fully enclosed nuclear membrane, contains the majority of the cell's genetic material, except for the mtRNAs and cpRNAs, all RNA is synthesized and then processed to a functional state in the nucleus.  

Endomembrane system

a group of membranes and organelles in eukaryotic cells

Endomembrane function

work together to modify, package, and transport lipids and proteins, systems specialized for protein secretion and membrane insertion

7 members of endomembrane system

Nuclear membrane, Rough ER, Smooth ER, Vesicles and Vacuoles, Golgi Apparatus, Lysosomes, Plasma membrane

Cell biology

study of the structure, function, and evolution of cells

Biogenesis

proposed that life only arose from pre-existing life.

spontaneous generation

life arose from inanimate non-living matter (such as air and soil); consistent with the religious dogma at the time that species on the planet were divinely created.  

Germ Theory

states that microorganisms are responsible for disease

unified cell theory

states cells are the most basic fundamental unit of life that can do all the functions of life (reproduction, metabolism, growth, response, and homeostasis), all organisms are composed of cells, and all cells come from pre-existing cells.

False

Both bacteria and archaea have DNA and RNA

Nucleolus

portion of the cell responsible for ribosomal subunit production 

Nucleus

Houses chromatin and is the site of RNA and DNA synthesis 

Ribosomes

RNA and protein complexes that catalyze a peptide bond between amino acids.

Vesicle

small organelles that transport proteins between the members of the endomembrane system

 Rough ER

reticulum with ribosomes that translate mRNA to peptides 

Golgi Apparatus

modifies and packages proteins for shipment 

Cytoskeleton

the filaments that provide the structure and support of the cell 

Smooth ER

reticulum without ribosomes that creates lipids 

Mitochondria

organelle responsible for ATP production (mtDNA)

Lysosome

organelles that houses hydrolytic enzymes 

Cytoplasm

semi-fluid medium in the cell.

Centrioles

produces filaments that play an essential role in cell division

Plasma membrane

consists of two sheets or layers of phospholipids that reside side by side forming a bilayer.

3 main functions of the cell membrane

1. Membrane proteins allow the regulated passage of ions, nutrients and waste. 

2. The amphipathic nature of the phospholipid bilayer allows the passive diffusion of gases such as oxygen and carbon dioxide. 

3. The membrane is covered with short carbohydrate chains that allow the interior of cells to sense and interact with their external environment.

4 molecular components

Phospholipids, cholesterol, membrane carbohydrates, membrane proteins

Location of phospholipids

Main fabric of the membrane

Location of cholesterol

Tucked between the hydrophobic tails of the membrane phospholipids

Location of Membrane Carbohydrates

found on the cell membrane

Location of Membrane Proteins

embedded within the plasma membrane

Directionality of the phospholipids

oppositely oriented(their heads exposed to the liquid on both sides and with the tails directed into the membrane)

Directionality of Cholesterol

Due to the hydroxyl group located at carbon 3, cholesterol is an amphiphile. In the membrane, this tends to orient cholesterol with the hydroxyl group facing water and the polar regions of nearby phospholipids to maximize hydrogen-bonding interactions.

Directionality of Membrane Carbohydrates

short oligosaccharides covalently bound to proteins (glycoproteins) or lipids (glycolipids), interact with molecules on the outside of the cell and help the cell communicate with its external environment.

Directionality of Membrane Proteins

Functions of Phospholipid

provide barriers in cellular membranes to protect the cell, and they make barriers for the organelles within those cells, and work to provide pathways for various substances across membranes.

Functions of Cholesterol

It stabilizes the membrane by resisting changes in fluidity, breaks up hydrophobic interactions between fatty acids, and the ratio of cholesterol to saturated versus unsaturated lipids impacts membrane fluidity.

Functions of Membrane Carbohydrates

help the cell communicate with its external environment. 

Function of Membrane Proteins

Transporting molecules across the membrane, facilitating enzymatic activity, signal transduction between cells, cell-to-cell recognition and communication, intercellular joining, and serving as an attachment point for the cytoskeleton and extracellular matrix.

2 main categories of membrane transport

passive diffusion and active transport

Passive Transport

a type of membrane transport that does not require energy to move substances across cell membranes.

Simple diffusion

the net movement of molecules from an area of high concentration to an area of low concentration

Osmosis

the net movement of water molecules across a semi-permeable membrane

Tonicity

the ability of an extracellular solution to make water move into or out of a cell by osmosis.

Facilitated diffusion

the passive movement of molecules across the cell membrane facilitated by specialized transport proteins

Channel proteins

Transmembrane proteins form a channel in the membrane to allow rapid diffusion of particles.  

Channel proteins can always be open or open in response to a stimulus.  If the channel is gated, it can allow very specific entry/exit of molecules in response to 4 types of stimuli: ligands, voltage, mechanical motion, or light.

Carrier Proteins

Transmembrane proteins bind to a solute and change shape to translocate the solute across the membrane.

Types of Gated Ion

channels, ligand, voltage, mechanical, light

Gated Ion Channels

allow for the flow of ions to occur through the channel

Function of Gated Ion Channels

Helping to maintain an electrochemical gradient across a chemical membrane.

Opening in response to a stimulus to allow ion flow.

Closing to allow the electrochemical gradient to reform.

Ligand Gated Ion Channels

use small molecules to trigger the channel to open and allow for ions to pass.

Voltage Gated Ion Channels

open in response to a change in charge across the membrane.  These types of ion channels are common in neurons and muscle cells.

Mechanical Gated Ion Channels

open in response to a physical stimulus. 

One example is how sound waves bend small projections inside ear cells that open ion channels.

Light Gated Ion Channels

are sensitive to visible wavelengths of light.

Active Transport

lets cells generate a concentration gradient using ATP energy

Protein Pumps are

Active transport proteins embedded in the cell membrane

Electrochemical Gradients

determines the direction that ions will flow through an open ion channel and is a combination of two types of gradients: a concentration gradient and an electrical field gradient

Sodium-Potassium Pumps(Na+/K+ pump)

pump involves an embedded protein (integral) that exchanges 3 Na⁺ ions (moves out of the cell) with two K⁺ ions (moves into the cell).  Sodium-potassium pumps require ATP to move ions across the membrane.

  An ATP is hydrolyzed, releasing a phosphate group to the protein.

The protein changes shape and the sodium ion is moved across the membrane.

The change in the conformation of the protein exposes the binding sites for two K⁺ ions

The phosphate group is released which returns the protein to its original shape

The K⁺ ions are moved across the membrane, completing the exchange of ions.

Proton Pumps

also known as a pH difference are active transport proteins that generate a proton gradient (H⁺) across a cell membrane. Proton pumps are found in all domains of life and are thought to be one of the first electrogenic pumps (able to create an electrochemical gradient).

Endocytosis and exocytosis

used by all cells to transport molecules that cannot pass through the membrane passively.

Secondary Active Transport 

Creates a concentration gradient using ATP and then coupling the driving force of the gradient to move solutes into a cell is commonly found in biology.   

Bulk Transport

The movement of macromolecules such as proteins or polysaccharides into or out of the cell

Endocytosis

the process of bringing molecules into the cell

Exocytosis

the process by which a cell transports secretory products out of the cell; both processes occur via membrane-bound vesicle pouches. 

Pinocytosis

cells ingest fluid and dissolved molecules from the medium outside the cell by enfolding them into a vesicle formed from the plasma membrane and then pulling them inside the cell.

Cell communication

able to respond to their environment,  send and receive messages from neighboring cells, and recognize and destroy pathogens

Reception of the signal

Cells can receive a signal on the external membrane or at an intracellular receptor.

  Transduction of the signal

 A series of chemical reactions, often phosphorylation events, that activate the target molecule.

Cellular response

change metabolism, the charge across the membrane, and a change in gene expression

Ligands

can be proteins or steroids, and they can travel far distances in the circulatory system to the target cell.

Direct contact signaling

signaling across gap junctions

Autocrine signaling

produced when the signaling cell and the target cell are the same or a similar cell (self signaling)

Autocrine signaling regulates

1. organism to ensure that cells develop into the correct tissues and take on the proper functions.

2.   Pain sensation

3. Inflammatory responses

4. Programmed cell death

5. Cellular differentiation during development

Paracrine Signaling

Signals that act locally between cells that are close together

Paracrine Signals

1.  Move by diffusion through the extracellular matrix.

2.  Elicit quick responses that last only a short amount of time. 

3.  Ligands quickly degraded by enzymes or removed by neighboring cells. 

 

Endocrine Signaling

Long distance signaling

Gap junctions in animals and plasmodesmata in plants

are connections between the plasma membranes of neighboring cells

Genetic Material of Gap Junction and plasmodesmata

filled with cytoplasm which allows diffusion of small ligands and ions into neighboring cells

Molecular specificity of gap junctions and plasmodesmata

ensures that the cells remain independent while allowing signals to be transmitted easily and quickly

Neurotransmitters

chemical ligands

Hormones

ligands released in endocrine signaling

Hormones form of transport

hormones get diluted and are present in low concentrations when they act on their target cells.

Intracellular receptors

Small hydrophobic ligands that can diffuse through the plasma membrane and interact with receptors inside the cell

Steroid Hormones

cholesterol-based lipids made of hydrocarbon skeletons with different functional groups attached

Peptide Hormones 

polar, water-soluble ligands and therefore cannot pass through the plasma membrane unaided

bind to cell-surface receptors

G Protein-Coupled Receptor

the largest and most diverse group of membrane receptors in eukaryotes. These cell surface receptors act like an inbox for messages in the form of light energy, peptides, lipids, sugars, and proteins.

Receptor Tyrosine Kinase Proteins

a subclass of tyrosine kinases that are involved in mediating cell-to-cell communication and controlling a wide range of complex biological functions, including cell growth, motility, differentiation, and metabolism