UNIT 1

Structure Of Human Cell :

Human cell is made up of several membrane bound cell organelles.

(1). Cell membrane :

Cell membrane is the outer covering of cell. It provides shape to the cell.

Cell membrane is made up of bi-phospholipid molecules.

It is a double membranous structure present in a cell.

Function of cell membrane:

• It separates the outer compartment of cell from its internal environment.

It helps in exchange of materials and substances In and out of the cell .

• It helps in providing a structure to the cell.

• It helps in keeping the cell organelles intact inside the cell.

(2). Cytoplasm :

• It is made up of three parts.

(1). Cytosol:

It is a gel like substance that is present inside the cell.

• Cytosol is the site of many chemical reactions inside the cell.

• It is a semi solid substance.

(2).Protoplasm :

Protoplasm consists of organic and inorganic substances such as protein,

nucleic acid, lipids, water and carbohydrates.

(3). Cell organelles:

These are small organs present inside the cell cytoplasm.

• Cell organelles are suspended inside the cytoplasmic metrics.

• Cell organelles include Endoplasmic Reticulum ,nucleus, Ribosomes, lysosomes , ,Centrioles, Golgi apparatus, Mitochondria, and other Microtubule structure .

(3) . Endoplasmic reticulum :

There are two types of Endoplasmic Reticulum.

Rough endoplasmic reticulum and Smooth Endoplasmic Reticulum.

Rough Endoplasmic Reticulum:

• It consists of series of interconnected tubules, which form a compartment

inside the cell called Lumen.

• Its surface is rough due to presence of ribosomes attached on its surface.

• Ribosomes are the site for protein synthesis.

Smooth Endoplasmic Reticulum:

• Smooth Endoplasmic Reticulum are smooth in surface. They are the site of lipid formation.

(4) Nucleus:

• It contains the genetic material of the cell.

• Genetic material is present in the form of DNA.

• DNA is a double helical structure.

• Nucleus is a membrane bound organelles.

• The outer membrane of nucleus is called nuclear envelope.

• Nucleolus is present inside the nucleus.

• Nucleus is the control center of the cell. It controls the functioning

of the cell.

Nucleolus: Nucleolus is the site for ribosome formation.

DNA: Deoxyribonucleic acid

• DNA is made up of protein . DNA contains the genes which contain information necessary for cellular functioning.

(5 ) Mitochondria :

• Mitochondria is a double membranous structure.

• Its membrane divides the lumen of mitochondria into two compartments.

• Outer compartment : Its membrane is smooth.

• Inner compartment: Inner membrane is present in the form of folds, which form cristae, which extend inside to the matrix.

• Matrix Is present inside the inner compartment of mitochondria, which contains certain proteins inside it. Function of Mitochondria:

• It is the site of aerobic respiration.

• Mitochondria helps in production of energy in the form of Adenosine triphosphate during chemical reactions . • Mitochondria is known as Powerhouse of the cell.

(6) Lysosomes :

• Lysosomes are vesicular structure, spherical in shape.

Function of Lysosome :

• Lysosomes are known as suicidal bags.

• They help in breakdown of cellular content or cell debris.

• Lysosomes contain hydrolytic enzymes such as lipase, proteases, which helps in breakdown of carbohydrate , protein and fat.

• Lysosomes help in removal of waste materials from the cell.

• Lysosomes clear the dead cell debris by engulfing them by a process known as phagocytosis.

(7) Vacuoles :

• Vacuoles are single membrane bound organelles found inside the cell.

Function :

• They help in removing waste material from the cell.

• It helps in storing nutrients and water.

(8) Ribosomes :

• Ribosomes are the site of protein synthesis.

• Ribosome size is 50S, 60S, 70S .

(9) Golgi Apparatus :

• Golgi Apparatus are flattened disk shaped structure .

Function :

• Golgi apparatus are the site of packaging.

• Proteins and lipids are transported to Golgi apparatus by rough and smooth endoplasmic reticulum.

• They change the structure of protein and lipids and package them for transporting to other organelles.

• Golgi apparatus are also known as protein factory

(10) Centrosomes and Centrioles :

• These are the structures which help in cell division.

• Centrioles are large shaped organelles made up of microtubules.

• During cell division, the centrioles moves to opposite side of Nucleus and form Mitotic spindle .

Centrosomes :

Centrosomes are found near the nucleus. They are centrally located.

Function :

• Centrosomes help in cell division by pulling chromatids apart during cell division.

• Chromatids are two halves of a chromosome that are replicated during cell division.

DIFFERENCE BETWEEN PROKARYOTIC AND EUKARYOTIC CELL

Prokaryotic Cell :

• Single Cellular.

• Cell Wall is made up of Peptidoglycan.

• Example of prokaryotic cell is bacteria.

• These cells are simple in nature.

• Prokaryotic cell is made up of a semi permeable membrane, made up of protein and phospholipid molecules. They have simpler membranous structure less lipid molecules are present as compared to Eukaryotic cell.

• They do not have membrane bound cell organelles.

• Nuclear envelope is absent.

• Nucleus is found free floating in the cytoplasm, In the form of DNA.

• Nucleolus is absent.

• Cell size is 1 to 10 micrometer.

• Ribosome size is 30S and 40S.

• Mitochondria is absent.

• Golgi apparatus is absent.

• Endoplasmic reticulum is absent

. • Lysosomes are absent.

• Centrioles are absent.

• Microtubules are absent.

• Single structured chromosome is present.

• Mode of reproduction is asexual.

Function of Human Cell :

• Cell provide structure and support to the body.

• Cell membrane of a cell help in transporting selective substances across its membrane .

• Cell take nutrients from the Food and convert them into the form of energy required for the body process.

• Mitochondria is the powerhouse of the cell, provides energy to the cell required for the cellular activity.

• Cell is responsible for thermogenesis.

• The nucleus contain the genetic information required for the Cellular activity of the cell.

• Cell help in formation of protein

• A cell has a property of reproduction.

• Cell replicates itself through cell division

• Cell help in metabolism and detoxification.

Type of Cell :

• There are two types of cell.

Prokaryotic and Eukaryotic Cell

Eukaryotic Cell :

• Multi cellular

. • Cell Wall in Plant cell is made up of cellulose, In human Cell, Cell Wall is absent.

• Example are plant Cell, animal cell, Protista and fungi.

• Eukaryotic Cell are complex in nature.

• Cell membrane of Eukaryotic cell is a selective semi permeable membrane made up of Bi-phospholipid molecules.

• These cells have membrane bound cell organelles.

• Nucleus is enveloped by a nuclear membrane

. • DNA is present inside the nucleus.

• Nucleolus is present inside the nucleus.

• Cell size is 10 to 100 micrometre.

• Ribosome size is 50S 60S and 70S.

• Mitochondria is present.

• Golgi apparatus is present.

• Endoplasmic reticulum is present.

• Lysosomes are present.

• Centrioles are present.

• Microtubules are present

. • Chromosomes are multiple in number.

• Mode of reproduction is sexual In human beings and animals, But Asexual in plants.

Cell division :

It is a process by which a parent cell is divided into two daughter cells.

Types of cell division :

Mitosis : This kind of cell division is involved in somatic cell.

Meiosis : This kind of cell division is involved in formation of sex cells or gametes .

Mitosis :

It consists of two phases. Karyokinesis and Cytokinesis :

(1)Karyokinesis : In this phase, the nucleus is divided into 2 daughter nucleus cell.

(1 ) Interphase (Preparatory phase)

(2) Mitotic phase (Actual cell division phase)

(1)INTERPHASE :

• It consists of three phases.

• Interphase is also known as preparatory phase.

• Cell prepare itself for division in this phase.

G1 Phase :

Metabolic phase .

• Metabolic activity increases in this phase resulting in increase in cell size.

S Phase :

• DNA Replicate itself for cell division.

• Two sisters strands of DNA called chromatids are produced during DNA replication.

G2 Phase :

• Protein replication occurs in this phase. Proteins are required for formation of organelles.

(2)MITOTIC PHASE :

• It is the phase where actual cell division take place.

• It consists of four phases.

• Prophase

• Metaphase

• Anaphase

• Telophase

(1)PROPHASE :

• In this phase cell membrane along with cytoplasm disappear.

• Nucleolus start disappearing in early phase of prophase.

• Sister chromatids of chromosomes’ condensed.

• Centrioles start moving to opposite side of chromatids and form spindle fibre .

• Spindle fibres are joined along the length of chromatids.

(2)METAPHASE :

• Chromosomes are aligned and raised around the metaphase plate.

(3)Anaphase :

• In this phase, the sister chromatids, which were present in pair, Move to opposite ends.

Cell becomes elongated in shape.

(4)TELOPHASE :

• It is the final phase of mitotic division.

• In this face, the chromatids arranged at opposite pole is converted to form new nucleus .

• The Division of nucleus is completed at Telophase .

• The Nucleus is finally divided into two daughter cell nucleus.

• Cell membrane and cytoplasm appears at the end of Telophase.

(2)CYTOKINESIS :

• It includes the division of cytoplasm and cell membrane into two daughter cells.

Cell membrane form furrows inside.

• Cell membrane form deep furrows, along with cytoplasm and two daughter chromatids.

• Deep furrowing progressively convert into formation of two daughter cells of each having their own cell membrane, cytoplasm, nucleus and cell organelles.