Cell Structure and Function

Discovery of the Cell

• Robert Hooke discovered the dead cell in 1665.
• Anton Von Leeuwenhoek discovered the first living cell in 1674.
• Robert Brown discovered the nucleus in 1831.
• Purkinjee gave the term protoplasm
• T.H. Huxley described protoplasm as "physical basis of life" in 1868.
• Rudolf Virchow stated "omnis cellula e cellula."
• The German botanist, Matthias Jacob Schleiden (1838), and British zoologist, Theodore Schwann (1839) gave the cell theory
• Further formalized by German researcher, Rudolf Virchow, in 1855, the theorem in modern form has four basic parts: the cell is the basic structural and functional unit of life, all organisms originate from pre-existing cells, all chemical and physiological functions are carried out inside the cell.
• Electron microscopes were invented by Knoll and Ruska.
• Scanning electron microscopes can examine the external parts of various organisms while transmission electron microscopes view the internal structure of organelles.

Number and Shape of Cells

• Multicellular organisms consist of more than one cell.
• An organism with billions of cells begins life as a single cell which is the fertilized egg(zygote).
• Unicellular organisms are single-celled and perform all of the functions that multicellular organisms perform.
• Shapes of cells in bacteria are of 4 main types: rod shaped (Bacillus such as Bacillus Subtilis), spherical shaped (Coccus such as Streptococcus sp.), spiral shaped (Spirillum such as Azospirilum), and comma shaped.
• Pleomorphism is the ability of few cells to change its shape during their life cycle and is seen in many bacteria, fungi and plant cells
• The white blood corpuscle (WBC) is the only animal cell that can change its shape.
• Eukaryotic cells include squamous, cuboidal, and columnar shaped cells, elongated muscle cells, thread-like neurons with extentions, flexible biconcave red blood cells, and cylindrical green alga (Spirogyra, Zygnema); cells in fungi are mainly long, branched and filamentous

Size and Cell Volume

• Large size of an elephant is due to large cells
• Cannot determine a relationship between cell and body size.
• The smallest objects that the unaided human eye can see are about 0.1 mm long, such as Amoeba, Paramecium)
• Cells are measured in Microns (abbreviation as um) with one micron equaling one-thousandth of a millimeter.
• Prokaryotic cells range between 1-10 µm
• Mycoplasma are the smallest cells at 0.1 μm
• Eukaryotic cell ranges between 10-100 µm.
• The largest cell is an ostrich egg at 18 cm.
• Ovule of Cycas is the largest plant cell.
• The longest cell is a neuron, up to 1m
• Cells that are metabolically more active should have larger surface area per unit volume

Structure and Function of Cell

• Basic components of a cell are cell membrane, cytoplasm and nucleus.

Cell Membrane Structure & Function

• Acts as selectively permeable barrier, fencing the majority of organically produced chemicals inside the cell while allowing few molecules (uncharged polar molecules) across it
• The cytoplasm and nucleus are enclosed withing the cell membrane, which is also called the plasma membrane.
• It separates cells from one another, as well as separating the cell from its surrounding medium.
• The plasma membrane is porous and allows movement inwards and outwards.
• mainly composed of lipids and proteins (phospholipid membrane).
• Proteins and cholesterol are scattered, while carbohydrates are on the surface, recognizing other cells by their glycoproteins and glycolipids.
• Peripheral proteins attach loosely to the inner or outer surface of the plasma membrane, while integral proteins lie across extending from inside to outside.
• Fluid mosaic model: A variety of proteins are scattered somewhat like "icebergs floating in the ocean"
• The fluid mosaic model was given by Singer and Nicolson in 1972

Membrane Protein Functions

• Channel proteins provide passage for certain hydrophilic or water-soluble substances such as polar and charged molecules, using facilitated diffusion
• Transport proteins spend energy (ATP) to transfer materials across the membrane using active transport
• Recognition proteins distinguish the identity of neighboring cells with oligosaccharide or short polysaccharide chains
• Adhesion proteins attach cells to neighboring cells or provide anchors for internal filaments and tubules
• Receptor proteins: initiate specific cell responses once hormones or other trigger molecules bind to them
• Electron transfer proteins: move electrons from one molecule during chemical reactions

Transport Across Cell Membrane

• Molecules in fluids move in response to gradients
• Movement across membranes occurs by both passive and active transport

Passive Transport Across the Cell Membrane

• Describes the movement of substances down a concentration gradient and does not require energy
• Bulk flow is the collective movement of substances in the same direction.
• An example is blood moving through a vessel.
• Simple diffusion is the net movement of a substance from an area of higher concentration to an area of lower concentration.
• Facilitated diffusion is the diffusion of solutes through channel proteins in the plasma membrane, whereas water can pass freely with the aid of specialized proteins(Aquaporins).
• Osmosis is the diffusion of water molecules across a selectively permeable membrane.
• Dialysis is the diffusion of solutes across a selectively permeable membrane.

Active Transport Across the Cell Membrane

• Involves movement of solutes against a concentration gradient and requires expenditure of energy, achieved through mechanism

Protein Pumps

• Transport proteins transfer solutes including (Na+, K+, Cl, H⁺), amino acids, and monosaccharides.
• Also known as ion pumps
• Protein binds to a molecule of the substance to be transported on one side of the membrane, then it uses the released energy (ATP.)
• Protein pumps are specific, with a different pump for each molecule.
• Protein pumps are catalysts for the splitting of ATP to form ADP and phosphate, thus called ATPase enzymes.
• Cystic fibrosis is a genetic disorder resulting in a misshapen chloride ion pump, resulting in the resulting production of thick mucus.

Vesicular Transport & Cell Surfaces

• Vesicles in the cytoplasm move macromolecules or large particles across the plasma membrane using types of vesicular transport
• Exocytosis: Vesicles contents fuse with the plasma membrane, releasing them outside of the cell.
• Endocytosis: The plasma membrane merges, capturing substance outside to engulf it and bringing it to the cytoplasm in a vesicle

Kinds of Endocytosis

• Phagocytosis or cellular: Dissolved materials enter the cell eating and plasma membrane engulfs the solid material
• Pinocytosis or cellular drinking: Plasma membrane folds inward forming a channel for dissolved substances to enter.
• Receptor-mediated endocytosis occurs: Specific molecules bind to receptors in the plasma membrane, resulting in inward folding and forming of a vesicle.
• Desmosomes attach cells
• Tight junctions make cells leakproof
• Gap junctions and plasmodesmata allow for communication between cells

Cell Walls

• Some cells are supported by cell walls
• An outer thick layer in cells of plants.
• Cells in plants need protection against variations in temperature, high wind speed, atmospheric moisture, etc..
• In plants, is composed of cellulose.
• The outer covering of other than plant cell,cell walls are bacterial/ fungal cells.
• Bacterial cells have walls of peptidoglycan(murein), while fungal cells have walls of chitin

Parts to the Cell Wall

• A young plant cell has primary cell wall, which is thin and flexible
• Between primary walls of adjacent cells is the middle lamella, a thin layer of polysaccharide (Ca and Mg pectate), gluing adjacent cells together
• Plant cells mature, hardening their walls
• Other plant cells add a secondary cell wall between the plasma membrane and the primary wall, for strong, rigid protection

Cytoplasm Components

• It is the jelly-like substance between the cell membrane and the nucleus containing (mitochondria, golgi bodies, ribosomes)
• Protoplasm includes the cytoplasm and the nucleoplasm, and is called the living substance of the cell.

Cytoskeleton Elements

• Thread like proteins that make up the cytoskeleton continually reconstruct to adapt to the cells constantly changing needs and maintain shape, and allow cells and their contents to move.
  • In cells of neutrophils and macrophages , this enables amoeboid movements
• The network is composed of microtubules, microfilaments or actin filaments, and intermediate fibers. - Microtubules are long hollow cylinders composed of tubulin. Microtubules form mitotic spindles, which partition chromosomes between two cells in cell division - Microfilaments have an arrow-like appearance and are made of the protein actin and move cells. Notable in muscle cells and white blood cells
• Microtubules, intermediate filaments, and microfilaments are three protein fibers of decreasing diameter and establishing the shape or movements of the cytoskeleton.

Cell Orgenelles

• Are bodies embedded in the cytoplasm that serve to physically separate metabolic activities from other substances.

Endoplasmic Reticulum & Golgi Apparatus

• Endoplasmic Reticulum: Is an interconnected canal of membranes that accounts for half of the membranes within a typical animal cell. Its canal system is composed of rough endoplasmic reticulum and smooth endoplasmic reticulum. -Rough Endoplasmic Reticulum (RER) consists of cisternae with ribosomes that synthesize membrane and secretory proteins which enter the ER membrane. - Enzymes within the golgi body add short chains of sugar molecules to proteins, changing them into glycoproteins (protein + carbohydrate = glycoprotein.)
  • Golgi apparatus (Middle man of cell): modifies, sorts and packages proteins into secretory vesicles and lysosomes. In plants, golgi body is in form of vesicles, known as dictyosomes.

Ribosome (Engine of cell/Protein factory of cell)

• Ribosomes are non-membranous cell organelles that are spherical bodies composed of RNA and proteins and are the platform upon which amino acids are assembled into proteins.
• Several ribosomes called polyribosomes (or polysomes) follow one another down the same messenger RNA molecule during protein synthesis, and are in two places

Ribosomes Location in cells

• Free: Suspended in cytosol, synthesize proteins that will be used in the cell.
• Bound: Attached to the outer surface of the membranous Rough endoplasmic reticulum, nuclear envelope, which is an extension.
• Present inside mitochondria and chloroplasts
• Ribosomes are of two types: 70S ribosomes, 80S ribosomes

Lysosomes, Centrosomes, & Perioxisomes

• Lysosomes (Food processor/digestive bags/Suicidal bags) are hydrolytic enzymes, some which hydrolyze proteins, polysaccharides, fats, & nucleic acids.
• Work closely with food vacuoles that hold food products waiting
• Centrosome is located in the cytoplasm attached to the outside of the nucleus and consists of two centrioles organized at right angles to each other & embedded in a mass of centrospheres.
• The centrioles have +0 arrangement of microtubules
• Peroxisomes: semi-spherical in shape and contain enzymes that take hydrogen from various substrates, bind it to oxygen, and create the by-product hydrogen peroxide (H2O2).
• They detoxify alcohol in the liver. Although, hydrogen peroxide is toxic, peroxisomes convert it into water.

Glyoxisomes, Sphaerosomes, Vacuoles

• Glyoxisomes are found only in plant seeds.
• Their function is to convert fatty acids into acetyl CoA for the glyoxylate cycle where two acetyl-CoA molecules are converted to a 4-carbon dicarboxylic acid.
• Sphaerosomes They are small spherical membrane bound plant lysosomes containing lipids and proteins, help in synthesis and storage of lipids.
• Vacuoles in plant cells are large
• Vacuoles are storage bins of substances that determine function such as storage of organic compounds.
• Contractile vacuoles are common in protozoan, found in some algae.

Energy Producing Organelles

• Mitochondrion: Power house of the cell.
• Mitochondria have two membranes. Outer contains transport proteins and inner has folds called cristae
• Cytosol ribosomes and ribosomes within the mitochondria itself create the mitochondrion.
• Chloroplast ; Kitchen of the cell and Uses solar energy to form sugar from carbon dioxide and water
• Plastids can be family members, including Chloroplasts, leucoplasts, amyloplasts, chromoplasts

Plant Componets

• Pili: String-like appendages attached to the outer surface of some prokaryotic cells, allow the cell to attach itself to other surfaces or cells, and in some, transfer DNA via conjugation.
• Cilia and flagella: used for movement. Microtubules encased in plasma membrane, Set up in a circle of nine pairs of microtubules with two singular microtubules in the center (9 + 2 arrangement).
• Leucoplasts: Colourless, storage plastids of storage - Aleuroplast :protein - Elaioplast :fats,
  • Amyloplast :carbohydrate
• Chromoplasts: Coloured Plastids
  • color comes from water soluble pigment Anthocyanin.

Nucleus & DNA

• Nucleus: Important, generally spherical orgncllae of the living cell.
  • Contains thread-like chromatin to carry traits via genes.
  • During cell division the chromatin condenses, coils into chromosomes with constrictions called centromere.
  • Chromosomes are DNA(Deoxyribonucleic acid & histone

Structure of Chromatin

• Nucleoprotein is called chromatin. With structure like beads on a string.
• According to the nucleosome-solenoid model, the beaded string is made of repeating units called nucleosomes.
• The segments of DNA joining the 'beads' are called linker DNA, which each have an of a histone protein (H1)
• Deoxyribonucleic Acid (DNA) is a complex megabiomolecule that forms a long chain molecule of repeating units called nucleotides, consisting of two polynucleotide each other along their lengths
• highly complex DNA molecule in composed of the three components: (i) deoxyribose sugar, (ii) a phosphate, (iii) nitrogen containing organic bases.
• DNA contains four different bases: Adenine, Guanine, Cytosine, and Thymine are in DNA.

DNA & The Watson-Crick Model

• The double helix double forms by two antiparallel polynucleotide coiled around each other in a right-handed helix, and held by hydrogen bonds
• Two strands yield alternate maior and minor grooves

Cell Division Basics

• In asexual (vegetative) reproduction, the resulting offspring, called clones, are genetically identical. Advantageous for rapid, effective spread of an organism
• Sexual repro: New individual formed by a combination of two haploid sex cells in the process called Fertilization. Gametes for fertilization usually come from separate parents
  • New individual formed = zygote, with two sets of chromosomes (Diploid)
  • Meiosis is a process to convert a diploid cell to a haploid gamete and cause a change in genetic diversity in the offspring.
• Karyotype is a pictorial display of metaphase chromosomes from a mitotic cell.

Chromosomes

• Ploidy is the Number sets of chromosomes in a cell -Haploid (n) - one set
• Diploid (2n) - two sets
• CELL CYCLE: Cell cycle is the process where:
  • G1 stage, cell prepares for DNA replication
  • S stage DNA replication occurs
• G2 stage, cell is preparing for nuclear (karyokinesis separate)
• Mitosis (cytokinesis) divides cells to new (cytokinesis)

Regulation

• Cdk (cyclin dependent kinase, adds phosphate to a protein), along with cyclins, are major control switches
• MPF (Maturation Promoting Factor) includes the CdK and cyclins.

Proteins That Regulate Cell Cycle

• P53 is a protein that is functions to block cell and damage DNA (i) p53 levels are increased in damaged cells, DNA by blocking the cell cycle. (ii) A p53 mutation is the most frequent mutation leading to cancer.
• Cancer is a disease where regulation of the cell cycle does not take place
• p27 is a protein that binds to cyclin and cdk by blocking entry into S phase.

Mitosis: Types of Cell Division

Process produces two identical cells

• What is mitosis? The cell cycle divided in G1 and S & G2 stage and Mitosis name proposed by Flemming

• What is Interphase ? This prepatory stage also subdivided into G1, S & G2 stage.

• What are Mitosis Prophases? Chromatin is nucleus condenses and the nucleolus disappears

• What are Mitosis Prometaphases? The nuclear membrane dissolves

Mitosis Metaphase, Anaphase, Telophase

• In Metaphase: Spindle fibers aligin the chromosome
• In Anaphase: The chromosomes at kinetochores and move to opposite sides of the cell.
• Telophase: cytoblasters at opposite ends of the cell where new membranes form

Cytokinesis & Errors

• The spindle fibres disperse and partitioning of cell begin
• The cell has contracted and will divide in 2, containing 1 nucleus, requires a cell plate, requires the help of golgi vesicles
• Meitotic error: Nondisjunction- homologues don't separate --> results in aneuploidy which is usally embryo lethal Trisomy

Meiosis & Overview

• In meiosis, a diploid cell produces two haploid daughter cells producing two daughter cells.
• Interphase is subdivided into G1, S & G2 in subsequent events of karyokinesis. This, like

Meiosis Prophase, Prometaphase, Metaphase

-Prophase: Longest phase with DNA strand replication allowing homologous chromosomes to to connect, known as bivalents with apparent recombination and chromosomal condensation.
- Prometaphase: With nuclear membrane dissolves, each attached chromosomes will will connect to the spindle fibers and being to to move.

Meiotic

metaphase I: Bivalents, each composed of chromosomes align, The orientation is random, meiotic anaphase I: Chiasmata separate movement to opposite and telophase, nuclear envelopes can start meiotic telophase I: Two complete daughter cells form with NO "S" phase: meiotic telophase II: Separates the homologes

Comparing Meiosis and Mitosis

• Chromosome Homologous:
• mitosis, chromosomes independent - meiosis, Homologous are paired forming bivalents
• Chromosome # -> mitosis identitical

• Meisosis:

• Daughter cells ->Identifical : Mytosis -> Hapliod genetics
• Progency -> identical = mitosis

• New + Not Identical

Chromoplastes & Pili

:Coloured plastids, and due to color found from water soubble pigment

• Found on some prokaryotic cells. are string like
• These structures are used by the cell in locomotion.

Nucleus

• Spherical central to cell, and separated by cytoplasm
• Has porous outer membrane,
• has thread like chromatin, and carries
• Chromosomes that are structures with constricrictions
• According to the nucleosome-solenoid model beads called nucleosomes create chromosomes

Cholorphyll

• Has several other components

Size and Wavelenght of Photosythis pigments:

Feature Chlorophyll a. Chlorophyll b Colour Blue green Yellow green Empirical. formula C55H72O5N4 Mg C55H70O6N4 Mg Watelenghte. 430, 662 nm 430, 644 nm

• Carotenoids that transfer energy to chlorophyll for use in photosynthesis

Photoshnthesis details

-Absorption is the graph showing light wavelengths rate, while an An action spectrum show that it respnds to graph

Mechinisims of Photsonsyhesis

• Light Rxn: In thylakpods (ligth absorion)
• The pigments are made from (LHCs)
• PHOTOSYSTEM-I/PIGMENT SYSTEM-1
• The reaction centre is P700.
• PS-I lies on the outer surface of the thylakoids.
• PS-I is found in both grana and stroma lamellae.
• PHOTOSYSTEM-II/PIGMENT SYSTEM-11
• The reaction centre is P680.
• PS-II occurs on the inner surface of the thylakoids
• PS-II is found in grana lamellae only. Non-Cyclic, Cyclic Photophosphorylation:The center absorbs wavelenght. Non can cause . H2O by splitting done by split.s
• CHEMI-OSMOTIC HYPOTHESIS:
• H+ concentration,
• proton gradient,
• proton pump
• ATPase
• C4 cycle is common to all plants, C3 as well as C4 plants
• is less expensive to the C3
• C3 Plants: I. Light intensity : There is a linear relationship between the carbon fixation II. Light quality : The best is white, followeed by red than blue light

C4 has many more steps for fixiation -> so less water is used

Cellular Repiration and Types:

• Repiration is biological (C–C ), release of energy in ATP. So all have it!

• Respiration substrate: is respiratory called substrates.

• Floating. ( carbs and fat) Protoplasmic -> with protein

• Unlike animals, plants do this to each other due to stomata. -> Aerobic respiration by water and CO,

• Anaerobic respiration

Glycolysis and Aerobic Respiration

• In the liver, the processes known as glycolysis results in the breakdown of molecule peruvate (in 2) ATP in mitrochondria

• How does anaerobic resiration happens? It occurs in when oxidation is done. Oxidative decarboxylation: which requires a catalyist kreb cycle needs to requires enzymes for membrane in the matrix of the cells

Electron transport and respiration

• ETS and phosphorylations: Oxidation with reduced enzymes
• Requires ETS : NADH, FADH

Plant tissues

• Are organized based on structure and function and are classified - Meristematic tissue is growth, dividing tissue as the location of cell division. - This occurs in primary growth(apical meristem) secondary lateral Meristem
• Types Of Meristem
  • Apical meristem
• Lateral and vascular expansion(horizontal expansion -Vascular (internal growth) - Cork Camium (external growth) Intercalary are found in related to plants , and is used for increased girth
• Secondary lateral meristem and plant growth

Permanent and Simple

• Permanent Tissues are formed by a specific and function taken up division

  • Simple permanent: tissue same types of cells in origin functions of Classofing is is as Parenchyma, colienchyma, and sclerenchyma.

• PARANCHYMA:

• Most like primive has intermoreclar spaces made of of cellulose- Function: like assistnence

• COLENCHYMA:

• Gum like cells are thin when cells are

• SCLERENchyma

• Infusion

• Theories are developed in the shoot — Thunica for 2 zones. TUnica is cover while corpus is body mass -> Hostogen in stem

• Dermatogen rise of stems to the

• Periblem the layer of of the contex

• Plerome :Central meristic

Genetics

• Genetics study heridity and variations of the phenotype of genes
• Gregor Menedel: The father of genetics

Laws , terminology

• Allels or allermorphs: A gene with 2 forms which are are the morphs
• Dominant: A trait which occurs in F1 generation of cross Recessive: One trait does not affect the Genotype: Genetic make up -> phenotype( genetic make-up that expresses what an org. is composed of)

Law and Test Crosses

Two types of Homos/Hetero organisms with the same or simelar phenotype and one of them always true Test comes where two gametype are self and are shown in in the following table. This has been for genetic variation

1. each parent donates

Today law of segregation

• Rule says test to help identify which occurs to show its valid. Today the multiple alleles exist .

The Law of Multiple Alles

• gene many is the amount in a population. the amount of 2 is not

Rule of Independent Asortment

Mendel did extend to dihybrid with data The parental constisted generation rYY ry Gives of F1 Y1 -Selfed generate F2

Chromosmes

• Coloured plastids, has water sollubble pigment They have a few selected types, also

Explore the fundamental aspects of cell biology, from cell activities and the invention of the electron microscope to multicellular organisms and cell shapes. Investigate organelles and their functions within the endomembrane system. Learn about cytoskeletal filaments and phagocytes.