cell the unit of life

Antonie von leeuwenhoek

Discovered the first living cell

Robert hooke

Saw a dead cell in 1665

Robert brown

Discovered the nucleus in 1831

Mathias schleiden

• A german botanist

• Observed plant cells in 1838

• Said that all plants are composed of cells that form tissue of the plant

Theodor schwann

• German zoologist

• Observed animal cells in 1839 and discovered the plasma membrane

• Also observed plant cells and discovered cell wall as the characteristic feature of plant cells

Rudolf virchow

• Modified the cell theory in 1855

• Cells arise from pre-existing cells

Exception of cell theory

Viruses

What is universal in all cells?

Plasma membrane, cytoplasm and ribosomes

Cell hypothesis

Schleiden and schwann

Unique features of plant cells

Cell wall, chloroplast and central vacuole

Cell membrane

• Made of lipids and proteins

• Semi-permeable

• Asymmetrical

Membrane bound organelle/nucleus

Found in eukaryotes but absent in prokaryotes

Nucleoid

A dense region of DNA in a prokaryotic cell (in place of membrane bound nuclues)

What is connected with similar RNA sequences and show prokaryotic organisations?

Mitochondria and chloroplast

Ribosomes

• Organelle within an organelle

• Found in mitochondria, chloroplast, and on rough ER

• 70s (30s + 50s) in prokaryotes and 80s (40s + 60s) in eukaryotes

Mycoplasma (size and shape)

• Smallest cell, also known as PPLO

• Doesnt have a cell wall

• Length - 0.3um

• Size - 0.1um

Erythrocytes/RBCs (size and shape)

• Round and biconcave

• Diameter - 0.7um

Leucocytes/WBCs (Size and shape)

Amoeboid and irregular

Columnar cells (shape)

Long and narrow, having basal nuclei

Nerve cells (shape)

Branched and very long

Tracheid cells (shape)

• Elongated

• Are a part of xylem

Mesophyl cells (shape)

Round and oval

Bacteria (size)

• Length - 3-5um average

• Size - 1-2um

Virus (size)

0.02-0.2um

Eukaryotic cell (size)

10-20um

Shape of a cell may vary

with function

Prokaryotic cells

• Bacteria, cyanobacteria and mycoplasma

• Smaller than eukaryotes and divide faster than them

Plasmids

• Smaller circular DNA providing unique phenotypic character to prokaryotes (such as resistance to antibitoics)

• Contains F-factor

Shapes of prokaryotes

Coccus (spherical), spirillum (spiral), vibrio (comma shaped), bacillus (rod like)

Genomic prokaryotic DNA

Is single chromosome circular DNA, packed by non-histone proteins

Gram positive bacteria

• Retains stain

• Has thick single layer cell wall

Gram negative bacteria

Doesnt retain stain for a long time and has a thin cell wall

Chromatophore

• An extension of the cell membrane in the cytoplasm that contains pigments; photosynthetic

• It is found in cyanobacteria

Prokaryotic cell wall

Most bacterial cell walls are chemically complex and are made of peptidoglycan

Glycocalyx

• The external structure of cell even outside of cell wall

• It is of two types ; loose sheath called slime layer providing hydration OR thick and tough protective capsule

What determines the shape of the cell?

Secondary cell wall

How does secondary cell wall form?

Forms outside the primary cell wall which starts shedding/degenerating

What part of cell interacts with the outside world?

Plasma membrane

Mesosome

• Extension of plasma membrane in the cytoplasm in the form of; vesicles, tubules and lemellae

• They help increase the surface area of the plasma membrane

What are the outer extensions of plasma membrane?

Flagella(motile), fimbriae(help with attachment), pili(movement)

Which prokaryote lacks flagellated cells?

Cyanobacteria

Inclusion bodies

• Unique to prokaryotes

• Stores reserve material like; phosphate, glycogen and cyanophycean granules

Gas vacuoles

• Also unique to prokaryotes, help with buoyancy

• Found in blue green and purple green algae

• Store metabolic gas

What is the size of ribosome?

15-20nm

Eukaryotes

• Has well defined nucleus

• Membrane bound organelles (except ribosomes and centrosomes)

• Complex cytoskeleton

• Genetic material is organised into chromosomes

Study of plasma membrane (Facts)

• RBCs were used to study plasma membrane

• 52% proteins and 40% lipids

• Has phospholipid bilayer

• Glycoprotein on the outer surface makes it asymmetrical

• Carbohydrates are also present

• Cholestrol present on surface to provide stability

Lipids and proteins of plasma membrane

Phospholipid (main lipids)

• hydrophobic non-polar tail

• Hydrophilic polar head

Proteins -two types

• integrated-hard to remove

• Peripheral-relatively easy to remove

Fluid mosaic model of plasma membrane

• Given by singer and nicolson in 1972

• Fluid nature of lipids help with cell growth, division, secretion and endocytosis

• Fluid nature provides flexibility for lateral movement of both lipids and proteins

• Flip-flop movement shown by lipids but not proteins

Passive transport

• no energy needed

• High to low concentration (along concentration gradient)

• Water - osmosis

• Neutral solutions - diffusion

• Polar solutes - facilitated diffusion (carrier protein)

Active transport

• energy is needed

• Low to high concentration (against concentration gradient)

• Na+ and K+ pump

Cell wall of plants

Cellulose, hemicellulose, pectin and proteins

Cell wall of algae

Cellulose, galactan, mannans and minerals like (CaCO3)

Cell wall of archaebacteria

Pseudomurein

Cell wall of eubacteria

Peptidoglycan/murein

Cell wall of fungi

Chitin

Middle lamella and plasmodesmata

• middle lamella- made of calcium pectate which holds/glues neighbouring cells together

• Plasmodesmata- connects cytoplasm of neighbouring cells

Single membrane cell organelles

Lysosomes, microbodies, vacuoles, golgi and ER

Double membrane organelles

Nucleus, mitochondria and plastids(chloroplast etc)

Endomembrane system

Includes ER, golgi bodies, lysosomes and vacuoles because they work in a coordinated manner

What does mesosome/cell membrane help with?

• Cell wall formation

• DNA replication and distribution to daughter cells

• Respiration and secretion

Endoplasmic reticulum

• Inside ER- luminal space; outside ER- extra luminal space

• Rough ER- makes proteins

• Smooth ER- makes lipids and steroids(in animals)

• Near the nuclear envelope continuous with the outer nuclear wall

Golgi apparatus

• discovered by camillo golgi In 1898

• Near the nucleus and ER

• Does packaging

• Size of its faces is 0.5-1.0um

• Has faces called cisternae; starting face is convex/forming/cis face and ending face is concave/maturing/trans face

How the golgi apparatus works

Proteins and lipids from ER come to the forming/cis face then move thru other cisternaes up till the maturing/trans face and leave the golgi body as a packaged glycoprotein and glycolipids

Lysosomes

• Suicide bags of the cell

• Hydrolytic enzymes present (hydrolases;lipases, proteases)

• Packaged in golgi

• Works in acidic pH

Vacuoles

• Store house

• Bound by tonoplast (membrane)

• Water, sap and excretory products stored

• Occupies 90% volume of plant cell

Tonoplast

Facilitates transport of number of ions against the concentration gradient

Mitochondria

• sausage like

• Diameter - 0.2-1um

• Lenght - 1.4.1um

• Semi-autonomous

• Aerobic respiration (Produce ATP)

• Ds circular DNA

• Has RNA molecules

• Double aqueous compartments

• 70s ribosomes

Stain used to observe mitochondria

Janus green

Plastids

• length - 5-10um

• Width - 2-4um

• Ds circular DNA

• 70s ribosomes

• Found in plant cells and euglenoids

Types of plastids

• chloroplasts (green)

• Chromoplasts (carotene and xanthophyl)

• Leucoplasts (white for storage)

• Amyloplasts (starch)

• Aleuroplasts (proteins)

• elaioplasts (fat, oil)

Number of plastids variation

• Chlamydomonas - 1 per cell

• Mesophyll - 20-40 per cell

Stack of thylakoids

Grana

Space in thylakoids

Lumen and thylakoids has pigments on it

Cytoskeleton of eukaryotes

• Filamentous proteinaceous structures consisting microtubules, microfilaments and intermediate filaments

• Involved in mechanical support, motility and maintenance of the shape of the cell

Cilia

• Hair-like outgrowths of cell membrane

• Small structures work like oars causing movement of either cell or surrounding fluid

• 5-10um size

• Work in a coordinated manner

• Help with attachment, feeding and sensation

Flagella

• hair-like outgrowths of cell membrane

• Longer structures responsible for movement

• 150um size

• Independent beating

• Has 3 components - basal body, hook and basal body

C.S. Of flagella/cilia

Nine doublets of radially arranged peripheral microtubules connected to central sheath by radial spokes and have a pair of centrally located microtubules singlets (9+2)

Centrosome and centriole

• 2 centrioles arranged at right angles to each other make 1 centrosome which help in division of animal cell (spindle formation) also helps making the basal body for flagella

• C.S. Of centriole - nine triplets, nine spokes, central hub (protein), cartwheel structure

Nucleus of a eukaryote

• usually one per cell

• But RBCs, sieve cells, zylem, fibre, etc dont have a nucleus

• Paramecium has 2 nucleus

Nucleus contains/ parts of nucleus

• Nucleoplasm

• Nucleolus (continuous with nuclear membrane cuz membrane less, active rRNA synthesis site, carries out protein synthesis)

• Chromatin (non-histone, histone proteins(+ve), DNA(-ve), and RNA(+ve))

• Nuclear pores - help in movement of RNA and proteins in and out pf the nuclear envelope

Nucleus staining

When stained by basic dyes by Flemming the material of nucelus that got stained was named chromatin

Chromosomes

• Chromatin gets packed to make chromosomes

• Centromere attaches them

• Kinetochore is present on the side of centromere which helps getting attached during division

• Non staining satellite also present

Types of chromosomes

Metacentric, sub-metacentric, acrocentric and telocentric