cell the unit of life class 11 NEET (not finished in the making)

what is cell

Is the fundamental structural and functional unit of life

Robert Hook

1st person to discover a cell. He observed a dead cell - cells of cork tissue (oak tree) through a hand made microscope.

• He wrote and illustrated The Micrographia, published in 1665

  • the first major work to share a scientist's observations made through a microscope.

Anton on Leeuwonhoek

Discovered the first LIVING cell that are capable of moving, such as bacteria, protozoa, spermatozoa and Erythrocytes (RBCS) under his own designed microscope.

Robert Brown

Discovered the nucleus

Purkinje

In 1839, he coined the term "protoplasma" for the fluid substance of a cell.

Thomas Huxley

protoplasm is the physical basis of life

Cell theory

Explains common characteristics and features in all living cells of organisms

• introduced by Mathias Schleiden Theodore Schwann

  • completed by Rudolf Virchow

Mathias Schleiden (1838)

German BOTANIST, widely studied all plants (anatomy)

• all plants are made up of different kinds of plant cells

Theodore Schwann (1839)

British ZOOLOGIST studied different types of animal and animal tissues

• discovered cell wall and plasma membrane

Rudolf Virchow

Studied cell division

“omnis-cellula e-cellula”

• new cells arise from pre existing cells through cell division

3 Points of cell theory

1. Cell is the structural and functional unit of all living organisms, they are made up of cells, and their product

2. New cells come form from pre-existing cells

3. Activities of an organism due to interactions and coordination functions between constitutive cells

Exceptions for cell theory

Viruses as they do not have unit membrane

• considered as neither living or non-living

  • as they live inside a host but do not live outside host

Porter

Discovered ER

Camille Golgi

Discovered Golgi body

Christian de Duve

Discovered lysosomes

Palace

Discovered ribosomes

Smallest living cells

Mycoplasma (PPLOS)

• 0.1-0.3um in diameter

  • do not have a cell wall unlike almost every bacteria

    • thus antibodies do not effect them

Ostrich egg

largest isolated single cell

• 14cm

Nerve cell

Longest single cell

• 0.1-1m in length

RBC (erythrocytes)

immature rbc - round and oval shaped, contains cell organelles

mature rbc - e-nucleated cell, biconcave - gets thinner to be able to move through the bloodstream easier

• they do not have any cell organelles to accommodate space for hemoglobin for the binding of oxygen

Leukocytes (WBC)

Amoeboid shape /irregular shaped

different types of wbc in my life processes flashcards

Epithelial cells

columna - long and narrow

• increases surface area for absorption

Mesophyll cells

round and oval shape - to accommodate more chloroplast

• are chief cells of leaf to perform photosynthesis

Tracheids

Thin and elongated narrow cells

• at maturity they loose protoplast

• transports water and minerals

Vibrio

bacteria that are comma , shaped

Bacillus

rod shaped

Spirillum

spiral shaped

Which kingdom doesn’t have unicellular organisms

Animalia also known metazoa (according to 5k classification)

Prokaryotic cell

‘Pro’ meaning before and “karyon” meaning nucleus

• have simple body organisation (cellular level)

• but have great varitaion in size and shape

• have great metabollic diversity

  • show all types of nutrition and behavior

ex) parasites, autotrophs, saprophytes

Cell envelope

3 layers

• glycocalyx

• cell wall

• cell/plasma membrane

Glycocalyx

Outermost layer of the cell envelope in a bacterial cell, also known as biofilm.

• viscious and gelatinous

• does not depend on whether the bacteria is gram + or gram -

• further divided into two types

  • Slime layer and capsule layer

Slime layer

Loose sheath, unorganized and non uniform in density and thickness

• provides protection from loss of water and nutrients

• helps to attach bacterial cell to another bacterial cell

Capsule layer

Thickand tough layer made up of polysaccharides (sugar)

• hides bacteria from host immune system

ex) Streptococcus pneumonia

• R-strain has no capsule, cannot cause pneumonia

• S-strain, capsule present, can cause pneumonia that can lead to death

Cell wall

Tough rigid layer, protects the bacteria from bursting/collapsing

made of peptidoglycan/murien layers

• non-living permeable layer

  • Permits entry/exit of water, gases, small molecules and ions

  • impermeable for large molecules (macromolecules) and undesirable molecules

peptidoglycan layer

polymers of NAM-NAG

• NAM - n-acetyl muramic acid

• NAG - n-acetyl glucosamine

  • connected by Beta-1,4 glycosidic bonds - lysosomes break this bond to kill bacteria

Peptidoglycan layers are connected by peptide cross bridges

Peptide cross bridges / peptidoglycan strands of the cell wall

responsible for stitching together layers of peptidoglycan to make the crosslinked meshwork of the cell wall.

these cross-bridges are also further connected with pentaglycin

Pentaglycine

connect the D-Ala and L-lys of different cross bridges

antibiotics

inhibits linking of peptidoglycan strands - cell undergoes lysis in the presence of antibiotics.

Lysis

breakdown of a cell caused by damage to its outer membrane

Gram staining

technique which is used to classify bacteria into two groups

• gram-positive and gram-negative bacteria

developed the gram staining process

Christian Gram

Gram staining process

1. Fixation of bacteria to glass slide by heating and drying

2. staining by crystal violet

3. add iodine - binds to the crystal violets and helps it attach to the bacteria

4. add alcohol - dissolves lipids, the glycocalyx of both the gram-negative and positive bacteria dissolve, and the outer lipoprotein layer of gram-negative bacteria dissolves.

5. wash with H2O - gram-positive bacteria are stained purple.

6. Stain with counter stain safranin (pink in colour) - binds with phospholipid bilayer (cell membrane) of gram-positive and gram-negative bacteria

End result : Gram-positive bacteria are stained purple and gram-negative bacteria are stained pink

Gram positive bacteria

Get stained crystal violet

• the cell wall of gram positive bacteria is thicker (20-80nm) and is made up of peptidoglycan

• more easily treated with antibiotics

Since safranin also attaches to the cell membrane in gram-positive bacteria, why doesn't gram-positive bacteria appear pink as well?

Becuase the pink colour of safranin is overshadowed by the deep colour of crystal violet, thus the pink is not shown.

Gram negative bacteria

Get stained pink by safranin

• The cell wall of gram positive consists of two layers, a lipoprotein layer and a peptidoglycan layer which is about <10nm

• harder to treat with antibiotics

Why does crystal violet dye not attach to gram negative bacteria?

Because the cell wall layer of gram negative bacteria is too thin, thus the violet crystal molecules get washed away.

Plasma membrane

Thin, flexible LIVING layer

• phospholipid bilayer

• selectively permeable layer

• Prokaryotic plasma membrane consists of hopanoids instead of cholesterol

Flagella

Tail like motile structure - gives mobility, allows the bacterium to move towards a favorable environment or move away from a hostile environment.

made with flagellin proteins

Atrichous bacteria

bacteria that does not have flagellum

Monotrichous bacteria

Has one flagella typically at one pole

Amphitrichous bacteria

Have 2 flagella typically at the poles

Peritrichous bacteria

flagella throughout the bacteria

Lophotrichous bacteria

Many flagella at 2 points of the cell

Cephalotrichous bacteria

Many flagella at 1 point of the cell

images of bacteria with flagellas

Structure of the flagellum of bacteria

Basal body, hook, filament

basal body

The structure of the basal body depends on whether it is a gram positive or gram negative bacteria.

Basal body in gram negative bacteria

consists of the L-ring, P-ring, S-ring, and M-ring all in order from the hook

L-ring is in the lipoprotein layer of the cell wall

P-ring is in the peptidoglycan layer of the cell wall

S-ring and M-ring is in the plasma membrane

all these rings are connected by a rod protein

Distal set

consists of the L and P-ring

Proximal set

consists of the S and M-ring

Basal body in gram postive bacteria

They only have one pair of rings , the proximal set consisting of the S and M-ring that are attached to the cell membrane

chemotaxis

Chemical stimuli

Phototaxis

Light stimuli

Pili/Pilus

Elongated tube like structure made up of Pilin protiens

• helpfull for conjugation

  • creates a long hollow tube called a conjugation pilus

  • helps to exchange plasmids between bacteria

• can help in movement (only with specific type of pili)

• true pili have only been reported in gram negative bacteria

Conjugation

False sexual reproduction

F+ bacteria

have pili

F stands for fertility factor

F- bacteria

dont have pili

Fimbriae

Filamentous bristle like fibers present on the surface of some bacteria

• made up of pilin protein

• helps to attach bacteria to rocks in streams or host tissue

No role in motility.

Mesosome

It is a membranous structure formed by the invagination of the plasma membrane - These extensions are in a form of vesicles, tubules and lamellae.

• helps in cell wall formation

• DNA replication and distribution to daughter cells

• aerobic respiration

• secretion process

• synthesis of the cell membrane

• increases surface area of plasma membrane and enzymatic content.

mesosomes are more prominent in gram positive bacteria than gram negative bacteria

Chromatophores (form of mesosomes)

referred to as pigment-containing cells or groups of cells that produce colour.

In some photosynthetic prokaryotes like cyanobacteria the chromatophores are the site of photosynthesis, its a plasma membrane infolding and contains chloroplast.

Ribosomes

Small, think granular structures present freely in the cytoplasm

• made of ribonucleo proteins

• S stands for svedbergh unit

  • unit depends on surface area and mass

• Mg2+ ions hold the two subunits of a ribosome together

Two types : 70-S and 80-S

Ribozyme

Catalyically active RNA molecule - forms peptide bond between 2 amino acids

all enzymes are proteins except ribozyme

70-S Ribosomes

Made up of 60 different types of proteins, 15-20 nm

Large subunit : 50-S contains 23-S rRNA & 5-S rRNA

Small subunit : 30-S contains 16-S rRNA

*23-S rRNA is the ribozyme

**prokaryotes only have 70-S ribosomes

Polysomes

Only in prokaryotes, made up of many 70-S ribosomes and a mRNA

80-S ribosomes

present in eukaryotic cells only

Contains -

Large sub unit : 60-S containing 28-S rRNA , 5.8-S rRNA & 5-S rRNA

Small sub unit : 40-S containing 18-S rRNA

• made up of 80 different types of proteins

Monosome

One 80-S ribosome and a mRNA

Inclusion bodies

Small thick granular structures present in cytoplasm

• ribosomes

• Storage food granules (consists of two types)

  • non membranous

  • Non unit membranous

Non-membranous storage granules

not covered with any membrane

ex) phosphate granules, cynaophycean granules

Non unit membranous storage granules

Covered with a non-unit membrane - protein layer (2-4nm thick)

Ex) sulphur granules, poly-b-hydrooxybutyrate, gas vacuoles

*a unit membrane is a lipid bilayer membrane like cell membrane