Biology notes
The cell walls of those eukaryotes are ==chemically== and structurally different form the prokaryotic cell walls.
Plant cell walls are composed of ==cellulose==.
Fungi cell walls are composed of ==chitin==.
A young plant cell is composed of primary and secondary cell wall
The ^^middle lamella^^ is the space between the adjacent plant cells.
The middle lamella is rich of ^^pectins^^ which glues the adjacent cell together.
Mature cells strengthen there walls by secreting hardening substances into the primary wall, or by adding a secondary cell wall.
Wood is strong because its consist mainly of secondary walls
The extracellular matrix of animal cells compensate the absence of the cell walls.
ECM composed of fibrous proteins, glycoproteins and proteoglycan molecules.
Collagen and the elastin are abundant proteins in the ECM .
Fibronectin attaches some cells to the ECM.
The fibronetin and other proteins are attached to integrins .
integrins bind in the cytoplasmic side with microfilaments and sometimes intermediate filaments.
Neighbouring cells often adhere via sites of direct physical contact.
If there are gaps or holes in the nonliving cell wall , cell to cell junctions will exist.
The cell membrane of the closed cells are connected to each other through the holes in the cell wall.
Plasmodesmata is the cytoplasmic connection between the two cells.
The plasma membrane lines the central tubule. It contains the central tubule.
Central tubule is a connection between endoplasmic reticules of adjacent plant cells.
Plasmodesmata unify most of the plants into one living continuum , that allows water other materials to pass freely from one cell to the another.
The cells share the same internal chemical environment its a result of plasmodesmata.
There are three cell to cell interaction in the animal cells , tight junctions, desmosomes, cap junctions.
The three junctions are common in epithelial tissue.
Epithelial tissues covers the internal and the external surfaces of the body.
Tight junctions contain proteins called claudins that prevent the passing of materials between the cells.
We are watertight because of tight juctions.
Desmosomes, also called adhesive or anchoring junctions, attach the cytoskeletons for both cells with the extracellular matrix.
Desmosomes are found in muscles and skin epithelium because of they are mechanically active.
Cadherin is a transmembrane protein that extracellular domain that join the cells togther.
Intermediate filaments (keratin) fix the desmosomes in the cytoplasm.
Gap junctions which is the communicating junctions , provide cytoplasmic channels from one animal cell to another, its like the plasmodesmata in plant cells.
The channel is consist of six identical proteins and arranged in circle.
The channel doesn’t pass proteins but other molecules it may pass them.
The channel it is like a gate open and close depending on Ca2+ and H+.
When the cell is damaged , its gap junctions closed by the flow of Ca2+ , that prevents other cells from damage.
The sandwich model , is the first attempt to describe the position of membrane proteins within the lipid bilayer.
The sandwich model is consist of two globular proteins layer and the phospholipid bilayer lies between them.
Singer and Nicolson model is the correct cell membrane structure(The fluid mosaic model).
Most membrane proteins are amphipathic.
The globular proteins are inserted in the phospholipids , the polar part is out of the membrane but the non-polar portions are in contact with non-polar interior of the bilayer.
Polar portions of protein maximise the interaction with water in the cytosol and extracellular fluid.
According to the degree of the association of protein with the membrane, Integral and peripheral proteins.
The cell membrane consists of four groups, phospholipid bilayer, proteins, cholesterol, carbohydrates.
The peripheral proteins are attached to the hydrophilic part of the phospholipid or to the integral proteins.
The integral proteins it could be partially embedded or completely embedded .
Plant cells have other sterols , but little or no cholesterol.
The cell surface marker are glycolipids and clycoproteins.
Membranes are not static sheets, they are dynamic.
Membranes is held together by hydrophobic interactions.
Most lipids and some proteins shift about sideways (lateral motion)
Lipids may flip flop across the membrane.
Proteins are larger than lipids, so they are much slower when they move.
Many of membrane proteins seem to be immobile.
The solidification happens when the phospholipids are closely packed , When the temperature decreases.
The solidification depends on the type of membrane lipids.
If the membrane is rich in unsaturated phospholipids, the membrane will remains fluid because of the kinks that prevent the packing of the hydrophobic tails.
The cholesterol works as a buffer , when the temperature is high (human 37T) the membrane will be less fluid semi-sold( because when T is high the membrane will be fluid), but at lower it do the opposite.
Membrane are very selective .
Membrane are sensitive to chemical messages , which are detected by receptor proteins.
There are transport in and out of membrane bounded intracellular compartments.
Lipid bilayers are impermeable to most essential molecules and ions.
The lipid bilayer is permeable to water and small uncharged molecules like oxygen and carbon dioxide.
The impermeable ions needs special transport mechanism.
Diffusion is the random movement of molecules down their concentration gradient.
The diffused molecule is unaffected by the concentration gradients of other substances.
The diffusion increase the entropy by spreading out particles, and decreasing its energy by spreading the particles from regions of high to low potential energy.
Diffusion is passive process
When the molecules pass across the membrane its called transport not diffusion.
There are there types of transport, passive transport and facilitated transport, active transport.
if the molecules pass through the transport proteins, this phenomenon is called facilitated transport.
Transport are very specific.
Transport proteins could be either channel proteins or carrier proteins.
Channel proteins provide hydrophilic passageway to allow waters and small ions.
Aquaporins are channel proteins facilitate the passage of water.
Carrier proteins undergo distinctive change in shape.
In simple passive transport, when the concentration of substance increase the rate of transport increases.
The rate of transporting through carrier proteins increases as concentration increases until a max level of transporting.
The quiz content.
Pro and euk cells share , cell membrane , cytosol , genetic material or chromosomes, have ribosomes.
The major difference between pro and euk is the DNA location.
In euk , ^^most^^ of the DNA is in the nucleus.
In pro, the DNA is in a nucleoid region.
Euk cells have compartmentation.
The logistics of carrying out cellular metabolism limit the cell size.
The smallest cells are mycoplasmas type of Bactria, they do not have cell membrane
The surface area and the distance affects the rate of transport in the cells.
Larger cells have high metabolic rates, because they have more cell machinery and require more energy to sustain their functions.
Organism made of small cells, because they allows for more efficient exchange of nutrients and waste products with the environment, easy to move around within the organism, easy to be replicated.
If the cell size increases its volume increase faster than its surface area.
Microvilli are thin projections which increase the surface area without a noticeable change in volume.
Bigger is better when mor details are revealed.
Resolution refers to the minimum distance between two points at which they can still be distinguished as separate entities.
The resolution of a light microscope is determined by the wavelength of light used to image a specimen, the refractive index of the imaging medium, and the angular aperture of the objective lens.
Pro are very important in the ecology of living organisms
Pro can harvest light by photosynthesis , while other break down dead organisms and recycle their components, some cause disease or used for industrial purposes.
The whole prokaryote operates as single unit.
the cell wall and capsule of bacteria play important roles in protecting the cell, maintaining its shape and facilitating the growth of the bacteria.
Archaea have unique membrane lipids that are composed of glycerol linked to hydrocarbon chains by ether linkages, unlike the ester linkages found in bacteria and eukaryotes.
Their cell walls can be composed of various chemical compounds, including polysaccharides and proteins, and possibly inorganic materials.
The machinery for DNA replication and protein synthesis in archaea is more similar to eukaryotic systems than to bacterial systems.
Archaea are similar to bacteria in terms of their prokaryotic cellular structure, but differ in their plasma membrane structure, cell wall structure, DNA replication, and gene expression.
They are more closely related to eukaryotic on a ^^molecular basis^^
Flagella are long, threadlike structures that protrude from the surface of a cell and are used for locomotion.
They can be found in varying numbers depending on the species.
Bacteria use their flagella to swim at high speeds by rotating them like screws, powered by the transfer of protons across the plasma membrane through a process called proton-motive force.
This coupling of an electrochemical gradient to rotational work is a fascinating feature of the bacterial motor.
Eukaryotic cells are more complex than prokaryotic cells, with ^^compartments^^ and %%organelles%% that allow for multiple biochemical processes to occur simultaneously and independently.
These cells have a cytoskeleton for support, a central vacuole in plant cells, and a membrane-bound nucleus that contains the genetic information for protein synthesis.
The nucleus is typically spherical in shape and located in the center of the cell, and most eukaryotic cells have a single nucleus, although some may have multiple nuclei.
The nucleolus is a dark-staining zone within the nucleus that is involved in intensive synthesis of ribosomal Rna.
The outer membrane of the nuclear envelope is continuous with the endoplasmic reticulum.
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