Download Cell - Lectures For UG-5

Cell and Cell Theory
Cell:
A cell is the smallest unit that is capable of performing life
functions.
Cell Theory:
 All living things are made of cells.
 Cells are the basic units of structure and function in all
living things.
 New cells are only made from pre-existing cells.
Different types of Cell
Prokaryotic Cell
Eukaryotic cell
There are two main groups of cells, prokaryotic and eukaryotic cells. They
differ not only in their appearance but also in their structure, reproduction,
and metabolism. However, all of the cells belong to one of the five life
kingdoms.
Prokaryote Characteristics
1.
2.
3.
4.
Simplest organisms: Very small in size.
Prokaryotic cells have no nucleus.
Lack membrane-bound organelles inside the cell
Have few internal structures that are distinguishable under a
microscope.
5. Genetic information is in a circular loop called a plasmid (instead
of having chromosomal DNA).
6. Strong cell walls, resistant to environmental changes.
All Prokaryotes are in the Monera kingdom.
 Bacteria,
 Archaea
Bacteria
•Are relatively simple single celled organisms. Because their genetic
material is not enclosed in a special nuclear membrane, bacterial cells
are called Prokaryotes from Greek word means Pre-nucleus.
• Bacterial cells generally appear in one of several shapes
Bacillus -Rod like
Coccus - Spherical
Spiral - Curved
Some bacteria are star shaped or square.
• Bacteria are enclosed in a cell walls that are largely composed of a
carbohydrate and protein complex called peptidoglycan.
• Bacteria generally produced by dividing into two equal cells; this
process is called Binary fission.
.
Modes of Nutrition
• For nutrition most bacteria use organic chemicals which in
nature can be derived from either dead or living organisms.
• Some bacteria can manufacture their own food by
Photosynthesis.
• Some can derive nutrition from inorganic substances.
• Many bacteria can swim by using moving appendages
called flagella
Archaea
•Archaea can be spherical, rod, spiral, lobed, rectangular or irregular in
shape. Some exist as single cells, others form filaments or clusters. Until
the 1970s this group of microbes was classified as bacteria.
•Like bacteria archaea consist of prokaryotic cells, but if they have cell
walls the walls lack peptidoglycan.
•Archaea often found in extreme environments are divided into three
main groups
Methanogens produce methane as waste product from respiration.
Halophiles live in extremely salty environment.
The extreme thermophiles live in hot sulfurous water.
• Archaea are not known to cause disease in humans.
Eukaryotes Characteristics
•
Eukaryotic cells are much more complex then prokaryotic
cells.
•
They all have a nucleus where the genetic material of the
cell is stored.
•
They have many organelles that work together to help the
cell function.
•
They can be just one cell or can make up more complex
multi-cellular organisms.
•
All plants, animals, fungi, and protists are Eukaryotic cells.
Fungi
• Fungi (singular Fungus) are Eukaryotes organisms whose cells have distinct
nucleus containing the cells genetic material (DNA) surrounded by a special
envelop called the nuclear membrane.
• Organisms in Kingdom Fungi may be unicellular or multicellular.
• Large multicellular fungi such as mushrooms may look like plants but they
cannot carry photosynthesis as most plants can.
• True fungi have cell walls composed primarily of substance called chitin.
• The unicellular forms of fungi yeasts are oval microorganisms that are larger
then bacteria.
Fungi
• The most typical fungi are molds. Molds form visible
masses called mycelia which are composed of long
filaments (hyphae).
• Fungi can reproduce sexually or
asexually.
• They obtain nourishment by absorbing solutions of
organic material from their environment whether soil,
sea water , fresh water, an animal or plant host.
Protozoa
•Unicellular eukaryotic microbes.
•Protozoa move by Pseudopods, flagella or cilia.
•Amoeba move by using extension of their cytoplasm called
pseudopods
•Other Protozoa have long flagella or numerous shorter
appendages for locomotion called cilia.
•Protozoa have a variety of shapes and live either as free entity or
as parasites that absorb or ingest compounds from their
environment.
•Protozoa can produce sexually or asexually
A few well known Protozoa
Algae
Algae are photosynthetic eukaryotes with a wide variety of shapes and both
sexual and asexual reproductive forms.
• The cell walls of many algae are composed of a carbohydrate called
cellulose.
• Algae are abundant in fresh and salt water in soil and in association with
plant.
• As photosynthesizers algae need light, water and carbon dioxide for food
production and growth and they do not generally require organic
compounds from the environment.
• As a result of photosynthesis algae produce oxygen and carbohydrates that
are then utilized by other organisms including animals, thus they play an
important role in the balance of nature.
Brown Algae
Diatoms
Different types of Algae
Green Algae
Different Eukaryotic Cells
Viruses
Viruses are very different from other microbial groups, they are so small
that most can be seen only with an electron microscope and they are
acellular (not cellular).
• They are obligate intracellular parasites. Grow and maintain their
structure by taking up chemicals and energy from the environment
• Structurally virus particle contains a core made of only one type of
nucleic acid, either DNA or RNA.
• This core is surrounded by protein core, sometimes the coat is encased
by an additional layer, a lipid membrane called an envelope.
• Viruses can reproduce only by using cellular machinery of other
organisms.
VIRIONS
They are virus particles. They are the INERT CARRIERS of the genome, and
are ASSEMBLED inside cells, from virus-specified components: they do not GROW,
and do not form by DIVISION.
Viroids and Prions
•
Viroids
– Naked RNA (no capsid)
– 300 – 400 nucleotides long
– Closed, folded, 3-dimensional shape (protect against endonucleases)
– Plant pathogens
– Base sequence similar to introns
•
Prions
Proteinaceous Infectious particle
Are the main cause of following Diseases:
– Scrapie (sheep)
– Creutzfeldt-Jacob disease (CJD)
– Bovine Spongiform Encephalopathy (BSE)
• Mad Cow Disease
Cell differentiation is a process in
which a cell develops into a specific
type of cell. This is the process which
allows a single celled zygote to
develop into a multicellular adult
organism that can contain hundreds
of different types of cells.
The organism will have
 Germ cells,
Somatic cells.
Why Do Cells Divide?
• Growth
• Repair
• Reproduction
(a) Reproduction: An amoeba,
a single-celled eukaryote, is
dividing into two cells. Each
new cell will be an individual
organism (LM).
(b) Growth and development.
This micrograph shows a sand
dollar embryo shortly after the
fertilized egg divided, forming
two cells (LM).
(c) Tissue renewal. These dividing
bone marrow cells (arrow) will
give rise to new blood cells (LM).
Binary Fission
Prokaryotic cells divide through a simple form of division called
Binary Fission.
Eukaryotic Cell Cycle
The cell cycle consists of
Interphase – normal cell activity
The mitotic phase – cell divsion
INTERPHASE
Growth
(DNA synthesis)
G1
Growth
G2
Interphase
Non dividing state with 3 substages.
 G1 stage: Cell grows in size, Organelles replicated.
 S stage: Replication of DNA , Synthesis of proteins
associated with DNA.
 G2 stage: Synthesis of proteins associated with mitosis.
Plant Cell
Animal Cell
Mitosis
• Process of forming identical daughter cells by replicating and dividing
the original chromosomes.
DNA duplication
during interphase
Diploid Cell
Mitosis
Phases of Mitosis
Prophase




Chromosomes Shorten and
become visible.
Centrioles move to opposite
sides of the cell.
Nuclear envelope disappears.
Spindle Fibers & Astral Fibers
both together are known as the
Spindle Apparatus begin to form .
Metaphase
Chromosomes line up along center
of cell called the Metaphase Plate
Chromosomes attach to spindle
fibers
Spindle & Astral fibers are now
clearly visible.
Anaphase
Centromeres break up separating
chromosome copies
Chromosomes are pulled apart to
opposite sides of cell
Spindle & Astral fibers begin to
break down
Telophase
Nuclear envelope forms around
both sets of chromosomes.
DNA uncoils.
Spindle & Astral fibers
completely disappear.
Meiosis
Reduces the chromosome number such that
• Each daughter cell has a haploid set of
chromosomes.
Ensures that the next generation will have:
– Diploid number of chromosome
– Exchange of genetic information
• Prior to meiosis I, DNA replication occurs.
• No replication of DNA occurs between meiosis I
and meiosis II.
Phases of Meiosis
Meiosis I
Prophase I
•Leptotene
•Zygotene
•Pachytene
•Diplotene
•Diakinesis
Metaphase I
Anaphase I
Telophase I
Meiosis II
Prophase II
Metaphase II
Anaohase II
Telophase II
Same
as
Mitosis
Prophase I
•During this stage, the
chromosomes begin to
condense and become
visible.
•Chromosomes become
denser.
• The homologous pairs
align with one another.
•Synaptonemal complex
form between
homologous pairs.
•Coiling and shortening
continues as the chromosomes
become more condense.
• A synapsis (Chiasmata)
forms between the pairs,
forming a tetrad.
Prophase I
•The sister chromatids begin to
separate slightly, revealing points
of the chiasma.
•This is where genetic exchange
occurs between two non-sister
chromatids, a process known as
crossing over.
•Chromosomes continue to pull apart, but
non-sister chromatids are still loosely
associated via the chiasma.
•The chiasma begin to move toward the ends
of the tetrad as separation continues.
•Also during diakinesis, the nuclear envelope
breaks down and the spindle fibers begin to
interact with the tetrad.
Meiosis I