cell unit of life detailed

How are all things classified?

Living (have living cells) and Non-living (do not have living cells).

What are the 2 groups of living organisms based on number of cells?

Unicellular (single cell, e.g. Amoeba, Bacteria, Paramecium) and Multicellular (two or more cells, e.g. Humans, Plants, Fungi).

What are the 3 key features of a cell?

: 1. A cell can live independently. 2. A cell can perform all essential functions of life. 3. Anything less than a complete cell cannot survive independently.

Who first observed and described a living cell?

Antonie Von Leeuwenhoek.

Who first discovered the nucleus in a eukaryotic cell?

Robert Brown.

What did the Electron Microscope reveal?

Fine structural details inside cells.

Who proposed the original Cell Theory and when?

Matthias Schleiden, german botanist (1838) and Theodore Schwann, german zoologist (1839). Together they proposed the original cell theory.

What did Schleiden observe?

Studied different plants and observed all plants are made up of cells. Groups of cells constitute tissue.

What did Schwann observe?

All cells are covered by a plasma membrane. All plant cells have an additional covering called cell wall. All plants and animals are made up of cells and products of cells (enzymes, mucus, hormones, blood plasma).

What is the limitation of the original Cell Theory?

It could not explain how new cells are formed.

What did Rudolf Virchow contribute in 1855?

Stated that new cells are produced by division of existing cells — "Omnis cellula e cellula" (all cells from pre-existing cells). This led to the Modified Cell Theory.

What are the 2 points of Modified Cell Theory?

1. All living organisms are made up of cells and products of cells. 2. All cells arise from pre-existing cells.

What is the smallest cell and its size?

Mycoplasma/PPLO (Pleuro-Pneumonia Like Organism) — 0.3 to 0.1 μm in length. It is also a bacterium.

What is the size of a typical bacterium?

3–5 μm / 1–2 μm.

What is the largest isolated single cell?

Ostrich egg - 14-18 cm

What is one of the longest cells?

Neurons

What is the diameter of a Human RBC?

7.0 μm in diameter.

In what 3 ways do cells vary?

Shape, size, and activity.

What are examples of different cell shapes?

Amoeboid, disc-like, cuboidal, columnar, and elongated cells.

What determines the shape of a cell?

The function it performs.

What is the shape of RBCs and why?

Round and biconcave — to accommodate more haemoglobin.

What is the shape of WBCs and why?

Amoeboid — to squeeze out of blood vessels.

What is the shape of Columnar Epithelial cells and why

Narrow and long — for absorption and secretion.

What is the shape of Neural cells?

Long and branched — to pass messages along themselves.

What are Mesophyll cells and their shape

Plant cells that are round and oval.

What are Tracheids?

Elongated plant cells.

What is a Virus and its size?

Not a cellular structure — size is 0.02 μm to 0.2 μm.

What are Prokaryotic cells? Give examples

Small, fast-dividing cells with diverse shapes and sizes. Examples: Bacteria, Mycoplasma, PPLO, Blue-green algae (Cyanobacteria).

What are the 4 bacterial shapes?

: 1. Bacillus — rod-shaped. 2. Coccus — spherical. 3. Vibrio — comma-shaped. 4. Spirillum — spiral-shaped.

What is fundamentally similar in all prokaryotes?

Cell organisation is fundamentally similar in all prokaryotes.

Peptidoglycan — made of amino acids and sugar. The cell wall surrounds the cell membrane. Exception: Mycoplasma lacks a cell wall.

Peptidoglycan — made of amino acids and sugar. The cell wall surrounds the cell membrane. Exception: Mycoplasma lacks a cell wall.

What is the cytoplasm of prokaryotes?

A semi-fluid matrix called cytoplasm that fills the cell.

What is the genetic material of prokaryotes?

1. Genomic DNA — naked, not bound by any membrane. 2. No true nucleus. 3. Circular, double stranded, single DNA molecule. 4. Represents a single chromosome. 5. Essential for survival. 6. Bacteria do NOT have RNA as genetic material — only viruses can have RNA as genetic material.

What are Plasmids?

1. Extra genomic DNA — not essential for life. 2. Circular, double stranded, small DNA molecules in cytoplasm. 3. Confer unique characters like antibiotic resistance. 4. Not essential for survival of bacteria. 5. Used in bacterial gene transformation. 6. Can self replicate.

What are the organelles of prokaryotes?

Bacteria has only ribosomes (70S) as its organelle. No membrane bound organelles are found in bacteria.

What are Mesosomes?

Infoldings of cell membrane — specialised, differentiated form of cell membrane. Characteristic of prokaryotes, more prominent in gram-positive bacteria. Forms: vesicles, lamellae, tubules.

What are the functions of Mesosomes?

1. DNA replication (only genomic DNA). 2. Distribution of DNA to daughter cells. 3. Aerobic respiration. 4. Cell wall formation. 5. Secretion. 6. Increase surface area of plasma membrane and enzymatic content.

What is the Cell Envelope and its layers?

A chemically complex, tightly bound three-layered structure found in most prokaryotes. Layers: 1. Outermost — Glycocalyx. 2. Middle — Cell wall. 3. Innermost — Cell membrane. Each layer has distinct functions but together act as a single protective unit.

What is Glycocalyx?

Outermost layer of cell envelope. Varies in composition and thickness. Made of polysaccharides but may contain proteins. 2 types: Slime layer and Capsule.

What is the Slime layer?

Glycocalyx when it is loose. Protects bacterial cell from loss of water and nutrients.

What is the Capsule?

Glycocalyx when it is thick and tough. Allows bacterium to hide from the immune system of the host body.

What are the functions of the bacterial Cell Wall?

Determines cell shape. Provides structural support. Prevents bacterium from bursting and collapsing. Made rigid by peptidoglycan (also called murine/mucopeptide).

How do antibiotics like Penicillin work on bacteria?

They inhibit cross-linking of peptidoglycan strands — so the bacterial cell undergoes lysis (breaks down) in their presence.

What is the Plasma Membrane of prokaryotes?

Selectively permeable. Interacts with external environment. Structurally similar to eukaryotic cell membrane.

What is Gram Staining?

A technique developed by Christian Gram to classify bacteria into 2 groups. Gram positive — retain gram stain. Gram negative — do not retain gram stain. Bacteria respond differently based on their cell envelope structure.

What are Chromatophores?

Membranous extensions other than mesosomes that extend into the cytoplasm. Present in some prokaryotes like Cyanobacteria and purple bacteria. Contain pigments for photosynthesis.

What is a Bacterial Flagellum?

Thin, filamentous extensions from cell wall. Present in motile bacteria. Each flagellum has 3 parts: Filament (longest, rigid, cylindrical, made of flagellin protein), Hook (curved portion connecting filament to basal body), Basal body (rod-like structure with various rings). Bacteria show a range in number and arrangement of flagella.

What are the rings of the Basal body of flagellum

L-ring and P-ring — associated with cell wall (distal set). S-ring and M-ring — associated with plasma membrane (proximal set).

What are Pili/Pilus?

1. Elongated, tubular structures. 2. Made of special protein called Pilin. 3. Do NOT play any role in motility. 4. True pili reported only in gram negative bacteria. 5. Involved in Conjugation — transfer of DNA from one bacteria to another through pilus. 6. Formation is generally controlled and specific.

What is Conjugation?

Transfer of DNA from one bacterium to another through pilus. Occurs only in gram negative bacteria via true pili.

What happens during Conjugation?

1. Takes place between compatible bacterial cells.

2. Usually partial transfer of DNA from donor cell to recipient cell takes place.

What are Fimbriae (singular - Fimbria)?

1. Small bristle-like fibres which sprout out of the cell.

2. Slender and composed of helically arranged protein subunits — 3-10 nm in diameter.

3. Help bacteria to attach to surfaces like rocks or host tissues.

4. Do not play any role in motility.

5. Made up of Fimbrilin protein.

What are Prokaryotic Ribosomes?

1. Associated with plasma membrane and also present in cytoplasm.

2. Size is 15-20 nm.

3. Made up of two subunits — 50S and 30S — forming 70S.

4. Site of protein synthesis (majority of enzymes are proteins chemically).

What is the difference between cytoplasmic and plasma membrane ribosomes?

1. Cytoplasmic ribosomes synthesise proteins that remain within the cell.

2. Ribosomes on plasma membrane make proteins that are transported out of the cell.

What are Polysomes/Polyribosomes?

1. Multiple ribosomes attach to a single mRNA to form a chain called polysomes or polyribosomes.

2. Ribosomes of a polysome translate mRNA into proteins.

What are Inclusion Bodies?

1. Unique to prokaryotes.

2. Function — storage of reserve material (stored for later use).

3. Not membrane-bound — present freely in cytoplasm.

4. Examples: Phosphate granules, Cyanophycean granules, Glycogen granules.

What are Gas Vacuoles?

1. Found in blue-green, purple and green photosynthetic bacteria (Cyanobacteria).

2. Non membrane-bound.

3. Can move around the cytoplasm.

What is a Eukaryotic Cell?

: 1. Typical size — 10-20 μm.

2. Found in Protista, Fungi, Plants and Animals.

What are the key features of Eukaryotic cells?

1. Complex structures — have locomotory and cytoskeletal structures.

2. Compartmentalisation — cytoplasm divided into different compartments with membrane-bound organelles.

3. Organised nucleus — contains nuclear envelope.

4. Genetic material is organised into chromosomes.

How was the cell membrane structure studied?

: 1. Detailed structure was studied only after the advent of the electron microscope in the 1950s.

2. Meanwhile membrane structure was being understood through chemical studies, especially on human RBC.

Composition of cell membrane in eukaryotic cells

Cell membrane of eukaryotic cells contain lipids

proteins

carbohydrates

and cholesterol

Main components of cell membrane of eukaryotic cell

Lipids and proteins

Major lipids present in eukaryotic cell? Their arrangement?

Major lipids are phospholipid and they are arranged in a bilayer

Each phospholipid molecule has two parts which are

Polar or hydrophilic head

(It faces outer side of membrane)

Non polar or hydrophobic tail

(Faces inner side of membrane)

What does the bilayered arrangement of phospholipids ensure

The bilayer arrangement of phospholipids ensure that nonpolar tails which are made up of saturated hydrocarbons are not exposed to aqueous environment.

they are neither exposed to cytoplasm and nor to extracellular fluid

The tails of phospholipid are made of

Saturated hydrocarbons

Where do the carbohydrate molecule get attached in the eukaryotic cells

Some carbohydrate or sugar molecules may be attached to the proteins or liquid molecules on the outer side of the cell

Carbohydrate attached to the protein form

Glycoprotein

Carbohydrate attached to lipids form

Glyco lipids

The presence of protein and lipid across the cell is varying in ratio or is it uniform

It is varying in ratio which means the amount is not fixed

Human RBC or erythrocyte’s membrane has around what percent of proteins and lipids?

52% protein

40% lipid

The cell membrane of eukaryotic cell is described as? and the protein present in them is described as?

The membrane is described as sea of phospholipids with protein as icebergs floating in it

Protein are of two types depending upon? What are the two types

The ease of extraction

Integral proteins

Peripheral proteins

What are integral proteins

Those proteins which are partially or fully embedded in the membrane

What are transmembrane protein? Give an example

Those integral proteins which span the lipid bilayer are called transmembrane proteins ( they are present across the membrane)

Eg: tunnel proteins

Are tunnel proteins difficult or easy to extract or remove? how can they be removed?

Tunnel proteins are difficult to remove

They require crude methods of treatment like detergents

What are peripheral proteins

Those proteins which just lie on the surface of the membrane and are not embedded at all

Who proposed the fluid mosaic model?

When

It was proposed by Singer and Nicolson

In the year 1972

What is the key concept of fluid mosaic model

According to this model, lipids have a quasi fluid nature which allows lateral movement of proteins

What is fluidity

The ability of protein to move laterally within the membrane is measured as its fluidity

What are the functions that the fluid nature of membrane can explain

Cell growth

Cell division

Intercellular junctions

Secretion

Endocytosis

One of the most important functions of the membrane

Transportation across membrane

Types of transport across membrane

Passive transport which is further divided into simple diffusion and facilitated diffusion

Active transport

What is simple diffusion

Movement of neutral or hydrophobic solute along the concentration gradient from high concentration to low concentration is known as simple diffusion

Facilitated diffusion

It is diffusion of polar molecules or ions which are hydrophilic from higher concentration to lower concentration that requires carrier proteins or channel proteins

Active transport

Some ions or molecules hydrophilic or hydrophobic are

transported against their concentration gradient

across the membrane

from lower concentration to higher concentration.

Example Na+ and K+ pumps in animal cells

Osmosis

Movement of water across membrane from higher concentration to lower concentration is called osmosis

It is a type of passive transport which occurs with or without channels

Non living and rigid structure in mature eukaryotic cell

Cell wall

Difference in cell wall which is immature and the one which is mature

Immature cell wall is living and flexible

Mature cell wall is non living and rigid structure

Cell wall is present in

Fungi and plant cells

Functions of cell wall

It provides cell shape

Provides protection from mechanical damage and infection

Helps in cell to cell interaction

Provide barrier to undesirable macro molecules.

Wards off attacks of pathogens like viruses bacteria fungi etc

the cell wall of fungi is composed of

chitin

A polymer of N-acetylglucosamine units

(NAG)

Cell wall of algae composed of

Cellulose

galactans

mannans

and minerals like calcium carbonate

Cell wall of plants is composed of

Cellulose which is an insoluble polysaccharide

Hemi cellulose

Pectin

and proteins

Cell walls are of two types which are

Primary cell wall and secondary cell wall

What is primary cell wall

The first formed layers in plant cells

What cell wall is present in young plant cells

Primary cell wall

What cell wall is capable of growth

Primary cell wall

What cell wall gradually diminishes as cell matures

Primary cell wall