Pravin V Jadhav, PhDAssistant Professor, MB & GE

Biotechnology CentreDr. Panjabrao Deshmukh Krishi Vidyapeeth ,Akola

GP 508 [2+1]Cell Biology and Molecular genetics

Why study cells?• Cells Tissues Organs Bodies

– bodies are made up of cells– cells do all the work of life!

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ATP

– “breathe” • gas exchange: O2 in vs. CO2 out

– eat• take in & digest food

– make energy• ATP

– build molecules• proteins, carbohydrates, fats, nucleic acids

– remove wastes – control internal conditions

• homeostasis

– respond to external environment– build more cells

• growth, repair, reproduction & development

The Work of LifeWhat jobs do cells have to do for an organism to live…?

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• Cells have 3 main jobs– make energy

• need energy for all activities• need to clean up waste produced

while making energy

– make proteins• proteins do all the work in a cell,

so we need lots of them

– make more cells• for growth• to replace damaged or diseased cells

The Jobs of Cells

Our organellesdo all these

jobs!

ATP

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The cell is the smallest unit of matter that can carry on all the processes of life

The invention of the microscope enabled Robert Hooke, (1665) and

Anton van Leuwenhoek (1675) to see and draw the first ‘cell’, a word coined by

Hooke

‘Cell Theory’ put forward – 1885

Cell Theory consists of three principles:

a. All living things are composed of one or more cells.

b. Cells are the basic units of structure and function in an organism.

c. Cells come only from the replication of existing cells.5

CELL DIVERSITY

Not all cells are alike.

Even cells within the same organism show enormous diversity in size, shape, and internal organization.

Around 1013 to 1014 cells in human body , of around 300 different cell types

CELL SIZE

A few types of cells are large enough to be seen by the unaided eye.

Most cells are small for two main reasons:

The cell’s nucleus can only control a certain volume of active cytoplasm.

Cells are limited in size by their surface area to volume ratio.

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CELL SHAPE

Cells come in a variety of shapes – depending on their function:-

The neurones from your toes to your head are long and thin;

Blood cells are rounded disks, so that they can flow smoothly

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Basic Cell Organization

All cells contain:

1.Cell membrane that keeps the inside and

outside separate.

2.DNA-containing region that holds the

instructions to run the processes of life.

3.Cytoplasm: a semi-fluid region containing

the rest of the cell’s machinery.

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Prokaryotes v. Eukaryotes

A Prokaryotic cell (bacterium) A Eukaryotic cell (plant)

Prokaryotes Eukaryotes

Typical organisms bacteria fungi, plants, animals

Typical size ~ 1-10 µm ~ 10-100 µm (sperm cells) apart from the tail, are smaller)

Type of nucleus Nuclear body [No nucleus] real nucleus with nuclear envelope

DNA circular (ccc DNA) linear molecules (chromosomes) with histone proteins

Ribosomes 70S 80S

Cytoplasmatic structure very few structures highly structured by membranes and a cytoskeleton

Cell movement Flagellae/cilia made of flagellin flagellae and cilia made of tubulin

Mitochondria none 1 - 100 (though RBC’s have none)

Chloroplasts none in algae and plants

Organization usually single cells single cells, colonies, higher multicellular organisms with specialized cells

Cell division Binary fission (simple division) Mitosis (normal cell replication) Meiosis (gamete production)

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B. CELL ORGANEELS

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Cell Organelles

• Organelle= “little organ”

• Found only inside cells

• All the stuff in between the organelles

is cytosol

• Everything in a cell except the nucleus

is cytoplasm

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Organelles of the cell1. Cell wall

2. Cell membrane

3. Nucleus

-Chromosomes

4. Cytomembrane system

5. Endoplasmic reticulum

6. Golgi bodies

7. Lysosome

8. Vacuoles

9. Centioles

10. Ribosome

11. Mitochondria

12. Plastids

a. Chloroplast

b. Amyloplast

c. Chromoplast 12

Cell wall

• Each plant cell is surrounded by a rigid

cell wall made of cellulose and

polysaccharides.

• The cell wall is outside of the cell

membrane.

• In woody plants, the cell walls can

become very thick and rigid.

• The cell wall, giving the cell its strength.

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Cell Walls

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Cell membranecell boundary

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• Function– separates cell from outside– controls what enters or leaves cell• O2, CO2, food, H2O, nutrients, waste– recognizes signals from other

cells• allows communication between cells

Cell membrane

lipid “tail”

phosphate“head”

•Structure double layer of fat• phospholipid bilayer receptor molecules• proteins that receive signals

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Cell Membrane, pt. 2

• The molecules in the membrane can move about like ships floating on the sea: the membrane is a two-dimensional fluid

• In some cells, the membrane proteins are held in fixed positions by a network of proteins just under the membrane, a cytoskeleton.

• Only water, a few gasses, and a few other small non-polar molecules can move freely through a pure phospholipid membrane. Everything else must be transported into the cell by protein channels in the membrane.

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Transport Across the Cell Membrane

Basic rule: things spontaneously move from high concentration to low

concentration (downhill). This process is called diffusion.

To get things to move from low to high (uphill), you need to add energy. In

the cell, energy is kept in the form of ATP.

Three basic transport mechanisms: passive transport for downhill, active

transport for uphill, and bulk transport for large amounts of material in either

direction.

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Passive and Active Transport• Passive transport uses protein channels through

the membrane that allow a particular molecule to go through it, down the concentration gradient.

• The speed and direction of movement depends on the relative concentrations inside and outside. Glucose is a good example: since cells burn glucose for energy, the concentration inside is less than the concentration outside.

• Active transport uses proteins as pumps to concentrate molecules against the concentration gradient. The pumps use ATP for energy.

• Ex: calcium pump, which keeps the level of calcium ions in the cell 1000 times lower than outside, by constantly pumping calcium ions out.

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Nucleus

• The nucleus issues instructions to build and maintain the cell, respond to changes in the environment, and to divide into 2 cells.

• The nucleus is surrounded by a double membrane called the nuclear envelope.

• The cell’s instructions are coded in the DNA, which is the main part of chromosomes.

• Each instruction in the DNA is called a gene. The genes issue their instructions, get expressed, as RNA copies.

• The RNA copy of a gene is called messenger RNA (mRNA). The mRNA instructions move out of the membrane into the cytoplasm, where they are translated into proteins.

• The translation of RNA messages into proteins is accomplished by ribosomes.

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Cytomembrane System

• The cytomembrane system is a group of organelles that has 3 basic functions:

– to manufacture new lipids and membranes,

– to modify polypeptides into their final proteins, and

– to synthesize and package proteins and other molecules for export.

• Organelles as part of this system:

– the endoplasmic reticulum (ER),

– the Golgi bodies,

– the lysosomes, and

– the peroxisomes21

Endoplasmic Reticulum

• “Reticulum” means network

• Connected to nuclear membrane

• Highway of the cell• Rough ER: studded with

ribosomes; it makes proteins

• Smooth ER: no ribosomes; it makes lipids 22

Endoplasmic Reticulum…

• Two types, connected together: rough ER and smooth ER

• Rough ER looks rough because it is studded with ribosomes, the cellular machines that synthesize proteins.

• Ribosomes on the rough ER make the proteins that go into the membrane, using the instructions from messenger RNA.

• Smooth ER has no ribosomes.

• It is used to synthesize the lipids of the membrane. It is also used in liver cells to detoxify harmful chemicals in the blood.

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Golgi Body and Secretion• Proteins that are synthesized in the rough ER get

finished in the Golgi body: sugars and phosphates added.

• Golgi looks like a series of stacked plates.

• Vesicles carry proteins from the ER to the Golgi, and then from the Golgi body to the cell membrane. Secretion to the outside world occurs by exocytosis.

• Proteins synthesized into the membrane of the ER end up in the cell membrane by the same mechanism

• Basic mechanism of secretion (Next Fig): – genes are copied into messenger RNA in the nucleus

– mRNA leaves the nucleus and attaches to ribosomes in the cytoplasm.

– the ribosomes move to the rough ER and synthesize new proteins

– proteins are transported by vesicles to the Golgi for finishing

– proteins are transported in other vesicles to the cell membrane, where they are released from the cell.

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DNA

RNA

ribosomes

endoplasmicreticulum

vesicle

Golgi apparatus

vesicle

Proteinon its way!

protein finishedprotein

TO:

TO:

TO:

TO:

nucleus

25Cytomembrane system & Making protein

small foodparticle

vacuole

digesting food

lysosomes

digesting brokenorganelles

Lysosomes# Garbage disposal of the cell# Contain digestive enzymes that break down wastes

• Function– digest food

• used to make energy – clean up & recycle

• digest broken organelles• Structure

– membrane sac of digestive enzymes

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Lysosomes and Peroxisomes

• Lysosomes are intracellular stomachs: they are full of digestive enzymes that operate at low pH.

• Vesicles transport materials to the lysosomes, and the lysosomes digest them.

• In the process of “programmed cell death”, cells scheduled to die are destroyed from within by their lysosomes.

• Example is the tail of a tadpole, which is destroyed to make a tailless frog.

• Lysosomal storage diseases are caused by genetic defects. Example: Gaucher disease, certain lipids accumulate inside of lysosomes instead of being broken down. It leads to interference with bone marrow function: blood and bone problems.

• Peroxisomes are membrane-bound sacs used to break down fatty acids and some other molecules. They generate hydrogen peroxide, a poisonous molecule, in the process, which is the source of the name peroxisome.

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Vacuoles

• Large central vacuole usually in plant cells

• Many smaller vacuoles in animal cells

• Storage container for water, food, enzymes, wastes, pigments, etc.

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Ribosome

That looks familiar…what is a polypeptide?

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Site of protein synthesis

Found attached to rough ER or

floating free in cytosol

Produced in a part of the

nucleus called the nucleolus

Plant Cell Organelles

• Plants have three special structures not found in animals: the chloroplast, the cell wall, and the central vacuole

• The chloroplast is the site of photosynthesis

• Like the mitochondria, chloroplasts have two membranes and their own circular DNA.

• Chloroplasts are also thought to have originated from an ancient mutually beneficial relationship between photosynthetic bacteria and a primitive eukaryote.

• In some plant cells, chloroplasts are modified to store starch (as in potatoes) or to contain other pigments (as in flowers).

Chloroplast

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Chloroplast

• Vary in size and shape

• Thylakoids– where photosynthesis takes

place

• Stroma– Calvin cycle– sugar synthesis

• The chloroplast has its own genome

CHLOROPLAST BIOGENESIS. 31

The MightyMitochondrion!

Powerhouse of the CellATP= energy

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Mitochondria

• “powerhouse of the cell”• ATP production• Cell “breathing” is called

cellular respiration• The mitochondrion has its

own Genome

Cellular respiration: converts sugars to energy (ATP)

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Mitochondria

• The mitochondria are the site where most of the cell’s ATP is generated, when organic compounds are broken down to carbon dioxide and water, using oxygen.

• All eukaryotes have mitochondria. The number in a cell depends on that cell’s energy needs.

• Mitochondria have their own circular DNA, the same kind found in bacteria.

• Mitochondria have 2 membranes, forming 2 compartments inside. To generate energy, hydrogen ions are accumulated between the 2 membranes. Then they flow down the concentration gradient into the inner compartment through a protein that uses the energy of their flow to create ATP.

• Genetic defects in the mitochondria affect tissues that use a lot of energy: nerves, muscles, liver, kidney.

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Plastids

• Contain pigments or storage products

1. Chloroplasts

2. Elioplasts [fat]

3. Amyloplasts [starch]

4. Leucoplast [terpens]

5. Protenoplast [proteins]

• Processing of circular dsDNA

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Quick Review

• Which organelle is the control center of the cell? Nucleus

• What is the stuff in between the organelles?Cytosol

• Which organelles are not found in animal cells?Cell wall, central vacuole, chloroplasts

• Which organelle helps plant cells make food?Chloroplasts

• What does E.R. stand for?Endoplasmic reticulum

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