Cytology: Cell Structure, Function and the Cell Theory

• Cytology is the study of cells.

Cell structure and function specialization

• The structure of cells is related to their specific functions.
• For example, skeletal muscle cells specialize in contraction.
• Nerve cells specialize in impulse carrying.

Modern Cell Theory

• Robert Hook first studied cork cells under a primitive microscope in 1665.
• He named the units "cells" from the Latin "cellula."
• Antonie van Leeuwenhoek handcrafted the first light microscope in 1674.
• Schleiden (botanist) and Schwann (zoologist) formulated the cell theory in 1838.
• Living organisms consist of cells and cell products, therefore the cell is the basic unit of life.
• Purkinje introduced 'protoplasm' in 1839 as the living substance of all cells.
• Virchow introduced biogenesis in 1858.
• All cells arise from pre-existing cells, i.e., life comes from life.
• All organisms are composed of cells as stated in the Modern Cell Doctrine.

Modern Cell Theory Statements

• Life occurs only in cells, making cells the basic unit for obtaining, converting, storing, and utilizing matter and energy.
• Cells are self-producing.
• Continuity of life relies on cellular components, like genes and chromosomes within the nucleus.
• Cells originate from the reproduction of previously existing cells.
• Structure is related to function.
• The structure of any cell is organized to execute its specific function(s).

Cell Definition

• A cell is the smallest structural and functional unit containing all structures and molecules essential for life.

Functions of Living Cells

• Responsiveness/Irritability, all living cells are able to react to a suitable stimulus.
• Conduction, the ability to conduct a stimulus along the surface of a cell, which develops highly in nerve cells.
• Respiration, is the oxidation of energy-rich molecules to release useful energy.
• Water and CO2 are by-products of respiration with O2 usually required.
• Anaerobic organisms are an exception that doesn't need energy.
• Contractility, ability of cells to change form after stimulation.
• Contractility develops highly in muscle cells to shorten the cell.
• Absorption, the ability to take up substances from surroundings to extract energy and synthesize molecules.
• Metabolism, the chemical processes in the body.
• It is subdivided into anabolism (building larger molecules) and catabolism (breaking down molecules).
• Secretion/Excretion, the release of essential or waste substances from the cell.
• Growth and reproduction, occurs by an increase in protoplasm or cell number after division.
• Cell size reaches a maximum, and further growth occurs via cell division.
• Cells are metabolically active units.

Metabolism

• It includes the synthesis of anabolism and the breakdown of catabolism chemical activities in a living cell.
• Foodstuff must be absorbed for to be metabolized.

Feeding

• Organisms assimilate materials for growth, maintenance, and energy
• Nutrients, inorganic (directly from the environment) or organic (carbohydrates, fats, proteins)

Organic Nutrients

• Autotrophic nutrition, like plants, synthesize organic food using inorganic compounds and sunlight (photosynthesis) or chemosynthesis.
• Heterotrophic nutrition is when organisms which includes animals, feed to degrading the organic molecules in other plants or animals

Respiration

• Oxidation of organic molecules to CO2 and H2O to gain energy.
• Organisms use absorbed food and worn-out body particles as 'fuel'.

Synthesis

• Complex cell building blocks synthesized from organic compounds.
• These reactions are usually reduction reactions, requiring energy.

Cell size

• Most falls between 10-100 μm in diameter, it is studied with a light microscope.
• Notable exceptions exist, such as egg cells from frogs or birds.

Minimum Cell Size

• The smallest cells, Mycoplasmas (obligate parasites), are about 0.1 μm in diameter.
• These are observed using an electron microscope.
• A minimum size is required for all necessary proteins to function.
• About 200 different proteins for the elementary form of life will not fit into a Mycoplasm.

Maximum Cell Size

• Multicellularity answers why large organisms don't consist of one huge cell.
• Biological communication is the advantage of smaller cells over large.
• Multicellular organisms have many small cells that function more effectively.

Surface/Volume Ratio

• Cells absorb substances and excrete products through the cell surface membrane (plasmalemma).
• A cell's surface should be large enough to accommodate the volume it contains.
• Volume increases at a rate faster than it's surface area which causes problems in nutrient uptake and waste excretion.
• The volume of the nucleus relates to the volume of the cytoplasm which limits protein synthesis that the nucleus can do.
• Substances move further by diffusion in large cells so small cells have a greater ratio of the surface area of the cell to the volume.
• Smaller cells have far greater surface area relative to their volume.
• Cells can increase only to a maximum size, with surface area enough to meet the needs of its volume.
• To grow further, cells divide into two smaller parts.

Specialization of Cells

• Multicellular organisms develop cell specialization to optimize metabolism in the cell.
• Special function examples, large plant cells, i) large vacuoles, vacuole's watery content (no participation in metabolism).
• ii) cytoplasmic streaming where organelles and fluids flow together through the cell.
• Eggs of birds, contain large amounts of food reserves and are not metabolically active cells.
• Skeletal muscle cells, more than one nucleus, are extremely long cells (fibres) for protein synthesis.
• Nerve cells, long narrow cylinders with all cytoplasm near the cell surface Micovilli, cytoplasmic projections from epithelial cells increasing surface area of the membrane without increasing the cell's volume.
• Microvilli are in epithelial cells of both the small intestine and kidney cells.

Methods of Studying Cells

• Microscopy is an important instrument in health sciences.
• Anything is studied with the help of a microscope (light, stereo, fluorescent, confocal, electron, etc.).

Light Microscope

• Cell structures were identified early in the 20th century.
• The microscope uses system of (glass) lenses to enlarge a mounted object.
• The resolving power is a microscope's ability to distinguish close points.
• For microscopes, the higher the resolving power makes it harder to see two nearby objects as one.
• Cell components, such as mitochondria and chloroplasts, are smaller than the resolving power of a good microscope.
• Cell components will show up as dots under a light microscope where there is no visible structure.
• To study cells with fine structure (ultrastructure), it is essential to use a microscope with a smaller resolving power, i.e., an electron microscope (EM).
• Electron microscopes use electron waves (instead of light waves) through magnetic lenses.
• Electron waves increase magnification ±250 000x and resolving power to 0.2 nm.
• This resolving power shows internal structure of cell components.

Transmission Electron Microscope (TEM)

• TEM focuses a beam of electrons on a specimen where some are absorbed and others are transmitted.
• Transmitted electrons build an image of the specimen on a television screen.
• Photographs taken of ultrastructures are known as electron micrographs.
• The fine structure of a mitochondrion is observed means of an electron microscope.
• Transmission-electron microscope takes electron micrographs showing a two-dimensional cross-section of the cell, magnified thousands of times.

Scanning Electron Microscope (SEM)

• SEM bombards the surface of a solid (massive) specimen with electrons.
• Reflected electrons are absorbed and yield a three dimensional image of the specimen (length, breadth and height).
• SEM studies bulky specimens because it has a high focus depth such as cancer cells.

Cell Fractioning

• Cell fractioning is a physical and chemical method to separate cell components.
• Differential centrifuging separates cell components.
• Clear suspensions of mitochondria separated and their biochemical activity is determined.
• Tissue is pulverized with a high-speed mixer and buffer medium to rupture the cells.
• Cell component contents (nuclei, organelles, enzymes) are separated in the buffer solution.
• The homogenate which contains all cell components is centrifuged at increasing speeds to separate and precipitate the various components.
• Components in the homogenate experiences greater centrifuge power due to higher speeds.
• Therefore larger cell components precipitate at lower speeds and smaller components precipitate at higher speeds.
• Fractions are studied to determine chemical composition, enzymes, and the different reactions associated with the cell.
• This process determined that mitochondria contain 52 enzymes involved in cellular respiration.
• As well, chloroplasts execute the complete process of photosynthesis.

Structural Organization of Cells

• All living organisms can be divided into the domains and kingdoms.

Domains and Kingdoms

• The domains include: Archaea, Bacteria, and Eucarya.
• The kingdoms include: Archaebacteria, Eubacteria, Protista, Fungi, Plantae, and Animalia.
• Cytology, cells divide into prokaryotes and eukaryotes, accordng to internal organization (nucleus).

Prokaryotic cells

• Typical of the Archaea and Bacteria kingdoms.
• Prokaryotic cells are primitive and small (0.5-3 µm) with a chromatin body (nucleus area) without a nuclear membrane.
• Therefore the nucleus of the cell is not delimited as a unit. There is, therefore, no true nucleus.
• The chromatin body includes a network of filaments, about 4.5 nm in diameter.
• DNA exists in the form of a circular DNA thread (without any histones or proteins).
• The chromosome occurs free in the cell at nucleoid.
• Some bacteria have small amounts of “extra” DNA in plasmids that are separated from the main chromosome.
• Plasmids are used in plant cells for genetic manipulation.
• A desired gene (e.g. for resistance against a herbicide) can be transferred to the plasmid.
• The plasmid is transferred to a plant cell and incorporated into its DNA.
• Desired gene can be expressed by the plant cell, therefore resistance against the herbicide.
• The cytoplasm has a membrane which is the plasmalemma along with a cell wall.
• Mycoplasms lack cells walls, being the parasites within plants and animals.
• These cells don't have any membrane-bound organelles like mitochondria or endoplasmic reticulum, but there are ribosomes.
• The only membranes within prokaryotes are a system of concentric membranes called a mesosome.
• It originates as invaginations of the plasmalemma, and is connected to the chromatin body.

Mesosome functions

• Enlarges the plasmalemma and increases surface area for respiration because respiratory enzymes are on the membranes.
• It is mostly concerned with the division of the DNA molecules after replication.
• Prokaryote cell walls are strong and have unique chemical compostion.
• The cell wall is a polymer compound called peptidoglycan (mucopeptide), along with other polymers like proteins, polysaccharides and lipids arranged to form one or more cell wall layers, 10 – 50 nm thick.
• Chemical composition of the cell walls between different bacteria groups differs.

Gram-positive vs Gram-negative bacteria

• Gram-positive bacteria are very thick walls with peptidoglycans.
• Gram-negative bacteria contain thinner walls with peptidoglycans.
• The walls are more complex comprising more than one layer.
• The inner layer mainly consists of peptidoglycans.
• The outer layer is composed of proteins, phospholipids, lipopolysaccharides (LPS).
• Chemical composition of the cell walls plays a role in susceptibility of bacteria to antibiotics.
• Penicillin inhibits the synthesis of peptidoglycans against Gram-positive bacteria.
• Penicillin is ineffective against Gram-negative bacteria because the outer layer with LPS blocks the antibiotic.
• Gram-classification determines therapy methods against different bacteria which includes what drugs to use.
• Staining Gram-positive, rinse with iodine solution and rinsing with alcohol/acetone, bacteria will stain.
• Stain on Gram-negative bacteria removed when alcohol/acetone is rinsed.
• Further coverings like slime (biofilm) or a capsule (polysaccharides and proteins) serves as a protective layer.
• Strains of streptococcus pneumoniae causing pneumonia without a capsule is engulfed if there is slime or capsules.
• Some prokaryotes have flagella (organsisms through surrounding fluid) or pili (surfaces and reproduction).

Similarities between Prokaryotes and Eukaryotes

• Both have DNA and use the same genetic code.
• Both synthesise proteins through RNA with ribosomes.
• Both use ATP as an energy source.
• Co-enzymes, e.g. NAD, KoASH execute identical functions in both with similar metabolism.
• Pro- and Eukaryotes originated from a common ancestor because of these fundamental similarities.

Eukaryotic Cells

• Except for Archaea and Eubacteria, all organisms are consisted of Eukaryotic cells type has a clearly demarcated nucleus surrounded by a nuclear membrane.
• Eukaryotic cells presents a definite evolutionary step after prokaryotes, there is more complexity and bigger.

Cellular components Definition

• Protoplasm is Basis of the living of the call and makes up the inside of a cell.
• Protoplasm composed of the cytoplasm and nucleoplasm.
• There are three things, Cytosol, organelles and inclusions, that makes up cytoplasm organelle which The translucent semi-gel fluid in which the organelles are suspended, Nucleus, ribosomes, the membrane-bound organelles as well as the cytoskeleton.
• Inclusions include a colloidal composed of proteins, lipids, carbohydrates, gasses and mineral ions
• Cell surface (cell wall and plasmalemma) are excluded from the cytoplasm

Definition of Cell organelle

• A cell organelle is a permanent structure within a cell.
• All organelles are surrounded by membranes, with the exception of ribosomes.
• Because of this, they represent separated compartments with unique contents and activity.
• The membranes of the nucleus and ER are continuous with the plasmalemma which originates through invaginations of the latter.
• Cytoskeleton, Eukaryotic cells possess a number of non-membranous structures that are not composed of membranes.

The Cell Organelles: STRUCTURE AND FUNCTION

• Some prokaryotes and eukaryotes have cell walls surrounding the plasmalemma.
• Structure differs to organisms, the plant cell walls are made of cellulose, the fungal cell walls of chitin, and bacteria cell walls are peptidoglycans and LPS.
• Function allows for protection, support and shape to the organism with being permeable to any substances.

The plasmalemma (cell membrane)

• The plasmalemma surrounds all living cells and it is the cell's most important organelle.
• The membranes surrounding the other the nucleus such as ER are almost identical to the cell membrane.
• Phospholipids form thin, flexible that has proteins that "float" in the phospholipid sheet.
• carbohydrates extend from the proteins.
• It is too thin to be seen under a light microscope
• Electron microscopy displays three-layers, Trilaminare - which Consists of two parallel dark, electron-dense lines, separated by a clear zone.
• The lipid is important and has fats, proteins and carbohydrates.

Lipids Structure and Function

• Phospholipids is the most abundant lipid in any membranes.
• A double layer of phospholipids contains less glycolipid and cholesterol.
• Consists of a polar part (phosphate) and a non-polar part (carbon chain).
• The polar part is hydrophilic (water-loving") and non polar is hydrophobic ("afraid of" therefore bind water and water can't bound to it).
• The function transports substances.

Cholesterol

• 50% of animal cell membranes contains cholesterol.
• It keeps the membrane fluid functioning.
• Membrane proteins float in a “sea” of membrane lipids.
• Ratio differs per membrane for each kind of protein and it ranges from 1:4 to 4:1.

Integral Proteins

• They stretch the proteins right through the membrane that interacts with both phospholipid tails.
• Integral protein functions provide Transport of substances, Act an for chemical reactions, for chemical signals from elsewhere
• Proteins on the inside surface of cell membranes interacts with cytoskeleton to cell's movement.
• Peripheral proteins: Attached either to the inside or outside surface of the membrane, or may be partially embedded.
• It interacts with the phospholipid heads only.
• Peripheral proteins are NOT within the membrane, therefore perform functions

Glycoproteins

• Polysaccharide chains (carbohydrate-component) the outer surface of integral, they are called Glyoproteins.
• Abundant glycoproteins is called a glycocalyx".

Carbohydrates

• Chains of oligosaccharides with phospholipids & proteins where various carbohydrates(polysaccharides) links to components in the membrane .
• Glycolipid is linked to lipids, whereas glycoprotein is linked to protein.
• Their function is the same such as Mediate between cells and Identifying markers.
• Serving as ID badges for the body to recognize transplanted tissue's carbohydrates is why transplants can be rejected .

Blood Type

• Blood type or blood group" is classified based on the presence or absence of substances on the surface of red blood cells.
• Antigens may be a combination depending on the blood group.
• General functions of the plasmalemma is the boundary between the cell and its environment.
• To maintain a selective barrier, regulate what comes, and also apply energy to force compounds with high activity in transport processes.

Communication

• External signals acts its as molecules by binding to signal and cause cascade of changes.
• The Molecules in acting as hormone receptors in that recognize bind with receptors in it by activates a second usually cyclic AMP, inbinds to initiate a change. in mix.
• Different kinds of cells recognise each other in this process.
• Intercellular interaction for communication provides attachment with other things.
• Animal cells forms the outer with extracellular materials such as cementing substances, There are excreted for calcium compounds.

Function

• Cellular communication via surface molecules forming molecules on the surface of membrane.

The Nucleus

• It Is the most obvious and largest structure exceptions are mature red blood.
• Function includes, Contains for entire organism (chromosomes), when the cell will produce any proteins and controls genes because froms the control center.
• Nuclear surface or membrane enclosed with double with smooth inside, that contains small that transport molecules and granular with liquid like substance.

Nuclear Membrane

• Prevents the entry of unwanted elements or molecule and ensure that the process like translation takes place .
• Chromosomes are long ,thin threads cell .
• DNA, histone proteins found through and duplicates where new cells obtain the DNA.
• Function occurs in nucleus: transfer of genetic material or information into parts can then through pores in the cell with mRNA acts is produced in transcription to translate parts in the translation process.
• Nucleoi - nuclear structures - produces sites for ribosomes as their proteins move the nucleoid to form units that come together with nucleus.

Ribosomes

• Small particles bounded to ER or nucleus.
• Ribosomes are also RND and Proteins like subunits of the proteins with constant amounts or values with the structure of density levels, size,and the protein they bound to.

Endoplamic reticulum

• Cytoplamic cell except red contains spaces - various tubules, sacs shape to partion the comp.
• Similar membranes has connections though smaller.
• Main function is to cells.

GER -Granular endoplasmic reticulum

• Structures with numbers called on the membrane is protein in amount , they can create protein or what it is.

Localization of Germinal vesicle

• Localization is what protein for the destination might: Synthesis with proteins. containment for protein for that.

• The ER membrane surface is smooth, with amount of for cell varies as the amount of it that may also have store elements where GER is located to produce elements.

SER- steroid

• It testorterone the production in ovaries, cortex muscle cells regulate.
• glycogen storage and reserve of the body.

Polysacheride

• Synthesis is detoxification - alcohol barituates in a liver.
• Liver enzymes produce the to detooxy certain chemicals to help cope or make or any damages that may become form damage.

The Golgi-complex

• Close proximity where close and around with that surrounded membranes shaped like a circle.
• It is to look like faces or in the middle.
• Membrane with secrertions.

Functions

• It where new , membrane can contain .
• Product is with exo,cy.
• Transport vesicle, in the cell process ,that proteins ,proteins accumulates, moves for its body that fuses and secrets content.
• lysosome stores cell - inter cellular.

Peroxisomes

• Structure with bodies or lysosmes surrounded membrane with some enzmes.

Function

• Synthesis de oxidation of molecules to help metabolize.
• Liver cells the alchohol to maintain and syntesihzize bile .

Mitochondria

• Only with cells for cells where shaped by that where the amount .

Double structure

• Layer with internal that contain which increase volume with other elements.
• The space area.

Functions:

• They can release their parts .

System

• All organelles membranes with functions and elements with segments by it with is similar by .

membrane flow Concept

• With membrane transfer and is
  The structure like from cell the is and the elements with by can that has support also.

Concept

• Few elements are rare in the that structures cell the and.
• Structures are nuclear with and with a support.
• Cyto is areas.

Skelteon

• A area or filaments .

• Micro: thin involved.

• Intermediate:

• Micro:

• Cell membrane with elements can .