BIOLOGY · 2020. 12. 22. · BIOLOGY . 2 Unit - I Lesson I - Cell: The basic unit of life Lesson II...

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Unit - ILesson I - Cell: The basic unit of life

Lesson II - Cell Cycle

Lesson III - Biomolecules

1.CELL

The Basic Unit of Life


Index

Cell: A short history of discovery

Types of Cells

Plant Cells and Animal Cells

Cell Organelles

Chromosomes and its types

Nucleic Acids and its types


Cell: A short history of discovery

▷ Cell: Basic Unit of Life▷ First found by Robert Hooke in 1665 found

the existence of cell under microscope and named it ‘cells’ relating to smaller rooms of monks known as Cellula.

▷ He discovered Cell by observing a Cork Cell▷ Anton van Leeuwenhoek in 1674 was the

first man to see a live cell and describe it.▷ Later Schleiden and Schwann found the

plasma membrane and formulated the ‘Cell Theory”

▷ The study of cell is known as Cytology


http://www.ucmp.berkeley.edu/history/leeuwenhoek.html

Types of Cells:

Prokaryotes

▷ A prokaryotic cell is a type of cell that does not have a true nucleus or membrane-bound organelles.

▷ Bacteria, archaea, protists, etc.

Eukaryotes

▷ Eukaryotes are organisms whose cells have a nucleus enclosed within a nuclear envelope. (A well-defined nucleus)

▷ Animal, fungi, plants, protozoa

Mesokaryotes

▷ As mesokaryotic cells contain a well-organised nucleus like that of eukaryotic cells, but its nucleus divides through amitosis like that of prokaryotes, so the cells are termed mesokaryotes which indicates its nucleus resembles both eukaryotic and prokaryotic nucleus.

▷ Few Protozoans, Planktons, etc.


Prokaryotic Cell VS Eukaryotic Cell:


Cell Type Prokaryotic Cell Eukaryotic Cell

Nucleus No Yes

DNA Arrangement Circular Linear

Size (diameter) (0.1 - 5) Micrometer (10-100) Micrometer

Unicellular Always Sometimes

Multicellular Never Usually

Animal Cell▷ Animal cells are surrounded by cell

membrane or plasma membrane.

▷ Consists of a gelatinous matrix called protoplasm which contains nucleus and other organelles which include the endoplasmic reticulum, mitochondria, golgi bodies, centrioles, lysosomes, ribosomes

and cytoskeleton.

Animal Cell and Plant CellPlant Cell▷ A Plant cell has prominent

cell wall.▷ The Cell Wall contains a

large central vacuole and plastids in addition to other organelles present in animal cell.


Animal Cell and Plant Cell


Animal Cell VS Plant Cell

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Cell Type Animal Cell Plant Cell

1. Usually smaller than plant cells Larger than animal cells

2. Cell wall absent Cell wall present

3. Vacuole small and temporary Vacuole large and permanent

4. Chloroplast absent Chloroplast present

5. Nucleus at the centre of the cell Nucleus present along the periphery of the cell

6. Lysosomes present Lysosomes are rare

7. Storage material is a glycogen granules

Storage material is starch grains

The Protoplasm and Cytoplasm

Protoplasm and Cytoplasm

● Cytoplasm is all the contents inside the cell membrane excluding the nucleus.

● Protoplasm includes cytoplasm, plus, the nucleus of the cell.


Cell Wall

▷ Cell wall is the outermost protective cover of cell. ▷ It is present in bacteria, fungi and plants whereas it is

absent in animal cell. ▷ It was first observed by Robert Hooke . ▷ In plant, cell wall shows three distinct regions

○ (a) Primary wall ○ (b) Secondary wall ○ (c) Middle lamellae.○

Functions of cell wall:

▷ Offers definite shape and rigidity to the cell.▷ Serves as barrier for several molecules to enter the

cells. ▷ Provides protection to the internal protoplasm

against mechanical injury.

Cell Wall and Cell Membrane


Cell Wall and Cell MembraneCell Membrane

▷ The cell membrane is also called cell surface (or) plasma membrane.

▷ It is a thin structure which holds the cytoplasmic content called ‘cytosol’.

Functions of Cell Membrane:

▷ Cell signalling▷ Transporting nutrients and water▷ Preventing unwanted substances

entering into the cell.


Endocytosis

Endocytosis is a cellular process in which substances are brought into the cell.

Endocytosis and ExocytosisExocytosis

Exocytosis is a form of active transport and bulk transport in which a cell transports molecules out of the cell by secreting them through an energy-dependent process.


Endocytosis and Exocytosis


Endoplasmic Reticulum :● The largest of the internal membranes is called the endoplasmic

reticulum (ER). ● The name endoplasmic reticulum was given by K.R. Porter

(1948). ● It consists of double membrane. ● Cisternae are long, broad, flat, sac like structures arranged in

parallel bundles or stacks to form lamella. ● When ribosomes are present in the outer surface of the

membrane it is called as Rough endoplasmic reticulum(RER),● When the ribosomes are absent in the endoplasmic reticulum it

is called as Smooth Endoplasmic Reticulum(SER).● Rough endoplasmic reticulum is involved in protein synthesis and

smooth endoplasmic reticulum are the sites of lipid synthesis.


Vacuoles:● In plant cells vacuoles are large, bounded by a

single unit membrane called Tonoplast. ● The vacuoles contain cell sap, which is a

solution of sugars, amino acids, mineral salts, waste chemical and anthocyanin pigments.


Golgi bodies:● In 1898, Camillo Golgi visualized a netlike reticulum of

fibrils near the nucleus, were named as Golgi bodies.● The Golgi apparatus compartmentalised a series of steps

leading to the production of functional protein.

Functions:

• Glycoproteins and glycolipids are produced.

• Transporting and storing lipids


Mitochondria :● It was first observed by A. Kolliker (1880). ● Altmann (1894) named it as Bioplasts and later Benda

(1897, 1898), named as mitochondria. ● Mitochondrion consists of double membrane, the outer

and inner membrane. ● The outer membrane is smooth and highly permeable

to small molecules and it contains proteins called Porins.

● The inner membrane is convoluted (infoldings), called crista.

● Mitochondria are called ‘Power House of a Cell’, as they produce energy rich ATP.


Plastids :● The term plastid is derived from the Greek word Platikas (formed/moulded) and used by A.F.U.

Schimper in 1885. ● He classified plastids into types according to their structure, pigments and function. ● Plastids multiply by fission.


Chloroplast:● Chloroplasts are vital organelle found in green plants.● Chloroplast has a double membrane the outer membrane and

the inner membrane separated by a space called peri plastidial space.

● Inner membrane of chloroplast is filled with gelatinous matrix, lipo-proteinaceous fluid called stroma.

● Inside the stroma there is flat interconnected sacs called thylakoid.

● Grana (singular: Granum) are formed when many of these thylakoids are stacked together like pile of coins.

Functions:

● Photosynthesis ● Light reactions takes place in granum● Dark reactions take place in stroma


Ribosome:● Ribosomes were first observed by George Palade

(1953) as dense particles or granules in the electron microscope.

● Each ribosome is made up of one small and one large sub-unit.

● Ribosomes are the sites of protein synthesis in the cell. ● Ribosome is not a membrane bound organelle. ● Ribosome consists of RNA and protein.


Lysosomes (Suicidal Bags of Cell):● Lysosomes were discovered by Christian de Duve

(1953), these are known as suicidal bags. ● They are spherical bodies ● They are enclosed by a single unit membrane.

Functions:

● Intracellular digestion:They digest carbohydrates, proteins and lipids present in cytoplasm.

● Autophagy: During adverse condition they digest their own cell organelles


Centrioles:● The centriole form the basal body of cilia or flagella and spindle fibers which forms the spindle

apparatus in animal cells.


Nucleus:● Nucleus is an important unit of cell which control all

activities of the cell. ● Nucleus holds the hereditary information. It is the

largest among all cell organelles. ● It is surrounded by a double membrane structure

called nuclear envelope. ● The membrane is perforated by pores known as

nuclear pores which allows materials such as mRNA, ribosomal units, proteins and other macromolecules to pass in and out of the nucleus.

● Nuclear space is filled with nucleoplasm.

Functions of the nucleus:

● Controlling all the cellular activities ● Storing the genetic or hereditary information.


Introduction to Chromosomes▷ Strasburger (1875) first reported its present in

eukaryotic cell.▷ The term ‘chromosome’ was introduced by

Waldeyer in 1888. ▷ Bridges (1916) first proved that chromosomes

are the physical carriers of genes. ▷ It is made up of DNA and associated proteins. ▷ The chromosomes are composed of thread like

strands called chromatin which is made up of DNA, protein and RNA.

▷ Each chromosome consists of two symmetrical structures called chromatids.


Structure of Chromosomes:● A satellite or SAT Chromosome are short chromosomal segment or rounded body. ● Based on the position of centromere, chromosomes are called telocentric (terminal centromere),

Acrocentric (terminal centromere capped by telomere), Sub metacentric (centromere subterminal) and Metacentric (centromere median).


Nucleic Acids:● It facilitates the transfer of genetic information from one generation to the next. ● Nucleic acids are big and complex molecules. ● They have a linear binding between nucleotides (DNA+RNA that contains a phosphate

group, a 5-carbon sugar, and a nitrogenous base).● They are double stranded and have highly complex sequencing.


Deoxyribonucleic Acid

▷ Better known as DNA this is the first type of nucleic acid.

▷ Contains the genetic material necessary for hereditary.

▷ DNA is made of four types of nucleotide: ○ Adenine (A) ○ Thymine (T) ○ Cytosine (C) ○ Guanine (G)

▷ The 'rings' of the DNA ladder are each made of two bases, one base coming from each leg.

▷ The bases connect in the middle: 'A' only pairs with 'T', and 'C' only pairs with 'G'.

▷ The bases are held together by hydrogen bonds.

Types of Nucleic Acids:Ribonucleic Acid

▷ RNA is our second type of nucleic acid. ▷ Although it does not get as much

importance as DNA, Ribonucleic Acid is absolutely essential for our survival.

▷ RNA is actually the blueprint of our DNAs. ▷ While the DNA is always inside the nucleus

of our cells, the RNA travels outside the nucleus to perform its functions.

▷ Ribosomal RNA: Is the main part of the ribosome, which is where the protein maker of our bodies.

▷ Messenger RNA: This RNA carries the message outside from the nucleus. It carries the information about what type of protein cells are to be manufactured.

▷ Transfer RNA: It brings the amino acid to the ribosome for protein production.


2.Cell Cycle


Index

Introduction

Mitosis

Meiosis


Introduction to Cell Cycle:● The cell cycle is termed a cycle because the events

repeat itself.● After completing one complete round the newly formed

daughter cells begin the same process all over again. ● The process of cell cycle promotes renewal and

regeneration of hair, blood cells, skin, and certain internal organs.

● The formation of daughter cells by cell division indicates the start of a new Interphase cycle. It is divided into 3 phases:○ G1 Phase - Growth Phase○ S Phase - Synthesis Phase○ G2 Phase - Growth Phase

● Cell is temporarily stopped progressing or somehow stopped dividing then the cell enter into another state termed as G0 phase (between M and G1 Phase), also called a “state of quiescence.”

● M-Phase: Meiosis and Mitosis


Mitosis

● Mitosis involves the exact replication of parent cell followed by its division into 2 daughter cells which are identical and contain the same number of chromosomes as in parent cell

● Strassburger (1870) - plant cells and Fleming (1882) - Animal cells● In plants, Mitosis occurs in the Meristematic cells or roots or the foot

tip.● Mitosis is divided into 4 stages:

○ Prophase○ Metaphase○ Anaphase○ Telophase

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01 02 03 04

Timeline

Stage - I Stage - II Stage - III Stage - IV

Prophase Metaphase Anaphase Telophase


Prophase

● Usually the longest phase of division

● Shortening and thickening of chromosomes

● Chromosomes composed of 2 chromatids held together by a centromere

● Nuclear envelope and nucleoli disappear

● Formation of spindle


Metaphase

● Chromosomes line up at the equator of the spindle or get aligned along metaphase plate through spindle fibres to both poles

● Spindle fibres attach to kinetochores of chromosomes

● Best phase to count and study the number and morphology of chromosomes


Anaphase

● The centromeres split into two and the spindle fibres pull the daughter centromeres to opposite poles.

● The separated chromatids are pulled along behind centromeres.


Telophase

● A reversal of prophase● Chromosomes become

de-condensed, uncoiled and form chromatin

● Nuclear envelope, nucleolus, Golgi complex and ER reformed

● 2 daughter cells are formed at 2 poles


Significance of Mitosis

● Production of diploid cells with identical genetic complement● Cell division helps to restore the nucleo-cytoplasmic ratio● Old or worn out cells are replaced by new cells formed through mitosis● Helps to increase the number number of cells within an organism


Meiosis

● Meiosis is a specialized kind of cell division that reduces the chromosome number by half which results in the production of haploid daughter cells.

● Meiosis involves 2 sequential cycle of nuclear and cell division known as Meiosis I and Meiosis II but have only a single cycle of DNA replication.

● Meiosis I is also known as reductional division (heterotypic division) because it brings about the changes from diploid to haploid stage.

● Meiosis II is also known as equational division (homotypic division) meant for maintaining haploid number.

● Meiosis involves pairing of homologous chromosomes and recombination between them.

● 4 haploid cells are formed at the end of meiosis II


Stages in Prophase-I


Leptotene● Beaded, Long Chromosomes● Chromosomes show bouquet

arrangement

I StageKey Features:


Zygotene● Chromosomes become shorter

and thicker● Bivalents or tetrad● Synapsis● Bivalents form synaptonemal

complexes to stabilize paired condition of chromosomes

II StageKey Features:


Pachytene● Longest stage (because it takes

time to crossover)● Tetrad now clearly appears as

spirally arranged chromosomes of homologous pair

● Crossing over occurs

III StageKey Features:


Diplotene● Bivalents repel each other● Chiasmata - sites of crossing

over) points strongly appeared.

IV StageKey Features:


Diakinesis● Terminalization occurs - the

terminal chiasma slips off the ends of the chromosomes

● Nuclear membrane disappears, centrioles migrate to poles and spindle fibres begin to form.

V StageKey Features:


Meiosis IProphase I:Long and Complex 5 step process

Metaphase I:Arrangements of chromosomes at equator & maximum condensation of chromosomes.

Anaphase I:Movement of homologous chromosomes without centromere breakage, nuclei form.

Telophase I:Chromosomes elongate and formation of 2 haploid cells

(reductional division)


Meiosis IIProphase I:Shortening and thickening of chromosomes

Metaphase I:Arrangements of chromosomes at equator & maximum condensation of chromosomes.

Anaphase I:Movement of homologous chromosomes without centromere breakage, nuclei form.

Telophase I:Chromosomes elongate and formation of 2 haploid cells

(equational division)


(All these phases are similar to the phases of mitosis.

Exception is that these process occur in 2 haploid cells and hence result in 4 haploid daughter cells

Stages in Prophase-I


Stages of Meiosis:


Significance of Meiosis

● Leads to formation of sex cells or gametes capable enough of engaging in fertilization

● Provides opportunities for new combination of genes to occur in the gametes by 2 ways - independent assortment and crossing over of chromosomes.

● Switches on the genetic information for the development of gametes.● Chromosomal and gene mutations can take place by irregularities of

meiotic division


3.Biomolecules


Index

Introduction to Biomolecules

1. Carbohydrates and its Classification2. Amino Acids3. Proteins4. Enzyme5. Vitamins and its Types6. Minerals


Introduction to Biomolecules:● Biomolecules is the molecules found in living organisms especially molecules found inside our cells. ● All living things are essentially made up of non-living atoms and molecules. ● Our bodies are made up of various of these complex biomolecules such as proteins, carbohydrates etc


Carbohydrates:● The term carbohydrate is a combination of the “hydrates of

carbon”. ● They are also known as “Saccharides” which is a derivation of the

Greek word “Sakcharon” meaning sugar. ● Some of the most common carbohydrates that we come across in

our daily lives are in form of sugars such as Glucose, Sucrose, Fructose, Cellulose, Maltose etc.

Classification of Carbohydrates:

The main classification of carbohydrate is done on the basis of hydrolysis.

● Monosaccharides● Disaccharides● Trisaccharides● Oligosaccharides● Polysaccharides


Classification of Carbohydrates:

Monosaccharides:

These are the simplest form of carbohydrate that cannot be hydrolyzed any further. They have the general formula of (CH2O)n. Some common examples are glucose, Ribose etc. Example : Beetroot , sugarcane , honey etc

Disaccharides:

Carbohydrates that give two units of the same or different monosaccharides on hydrolysis. For example, sucrose on hydrolysis gives one molecule of glucose and fructose each. Whereas maltose on hydrolysis gives two molecules of only glucose,

Trisaccharides:

Carbohydrates that on hydrolysis gives three molecules of monosaccharides, whether same or different. An example is Raffinose

Oligosaccharides:

Carbohydrates that on hydrolysis yield two to ten smaller units or monosaccharides are oligosaccharides. They are a large category and further divides into various subcategories.

Polysaccharides:

These give a large number of monosaccharides when they undergo hydrolysis, These carbohydrates are not sweet in taste and are also known as non-sugars. Some common examples are starch, glycogen etc.

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Importance of Carbohydrates:

● Carbohydrates are responsible for storing chemical energy in living organisms. They provide extra energy to the body.

● They are also an important constituent for supporting tissues in plants and even in some animals.

● Photosynthesis: It is the process by which plants utilize solar energy to generate energy for themselves and food for us.


Amino Acids:● There are some 20 amino acids in the proteins that we consume.● These amino acids bond together to form a larger protein molecule. ● These are an essential nutrient in our diet because of the functions they perform.● Amino acids are the building blocks of proteins.


Protein:● Proteins are what we call biological polymers (i.e. they occur naturally in nature). ● Proteins are long chain-like structure, with amino acids being the main ingredient. ● These amino acids are connected together with peptide bonds, and a few such bonds linking together form a

polypeptide chain.● One of the smallest protein molecules is insulin, and the largest being Titin which consist of 34,350 amino

acids.


Enzyme:● There are hundreds of reactions that occur in our body to absorb

the nutrients from food. ● The catalyst for all these reactions is enzyme.

Classification of Enzymes The classification of an enzyme is on the basis of the reaction they catalyze. The classification is as follows

1. Oxidoreductases: Catalyze oxidation-reduction reactions2. Transferases: These obviously catalyze reactions of group

transfer 3. Hydrolases: Hydrolysis reactions are catalyzed by them Lyases:

one of the lesser known enzymes 4. Isomerases: These change the shape of the molecule after

catalysing its structural shifts 5. Ligases: These catalyze ligation processes


Vitamins:● Vitamins are a group of organic compounds that are extremely

necessary and essential for normal growth and functioning of the human body.

● They are required in very small quantities but cannot be synthesized by the body itself, and can only be sourced from outside.

● Whereas they are not possible to be synthesized in our bodies

Types of Vitamins:

Around 17-20 types have been discovered and studied up till now. They mainly fall into two classifications, namely

1. Fat Soluble Vitamins2. Water Soluble Vitamins


Fat Soluble Vitamins▷ As the name suggests these are soluble in lipids

i.e. in fats. ▷ They are insoluble in water. ▷ Their absorption into the bloodstream happens

in the intestines. ▷ They are stored in human bodies as adipose

tissues in the liver. ▷ Fat-soluble types of the vitamin are not easily

excreted, Hence it is very much possible to overdose on them if they reach toxic levels in your body, This disease is Hypervitaminosis.

▷ The fat-soluble Vitamins are Vitamin A, D, E and K.

Types of Vitamins:Water Soluble Vitamins▷ These are readily

dissolvable in water. ▷ Excess water-soluble

vitamin in your body passes out through urine.

▷ Since they are excreted so easily they also need to be replaced regularly.

▷ Water Soluble Vitamins are Vitamin B and Vitamin C.


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Vitamin Found in Deficiency Disease Symptoms

Vitamin A Fish oil, egg, milk, ghee, carrot, corn, yellow fruits, greens

Night blindness Poor vision, difficulty in seeing in dim light

Vitamin B Whole grain, unpolished rice, milk, fish, meat, peas, lentils Green vegetables

Beriberi Nervous weakness, fatigue

Vitamin C Oranges, Gooseberry, Green Chilli, Tomato

Scurvy Bleeding gums

Vitamin D Green Chilli, Tomato Scurvy Bleeding gums Vitamin D Fish oil, milk and eggs. It is also made in our skin using sunlight

Rickets Weak, flexible bones

Vitamin E Vegetable oils, Green vegetables, whole wheat, Mango, apple, greens

Nervous weakness, dimming of eyesight

Childlessness, lack of resistance power to illnesses

Vitamin K Green vegetables, Tomato, cabbage, eggs, milk products.

Weakness of the bones, teeth etc.

Even a small cut bleeds profusely.


Minerals:● Minerals are required for growth as well as for the regulation of

normal body function.● Green leafy vegetables like spinach, pulses, eggs, milk, fish and

fruits are important sources of minerals in our diet.● Minerals are also known as ‘Protective Foods’.

Minerals Functions:

1. Calcium Strong bones and teeth2. Clotting of blood Phosphorus3. Iodine Synthesis of thyroid hormone 4. Iron Formation in haemoglobin 5. Brain development


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BIOLOGY · 2020. 12. 22. · BIOLOGY . 2 Unit - I Lesson I - Cell: The basic unit of life Lesson II...

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