The World of Cells

1. The World of Cells

2. 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.

3. 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.

6. Prokaryote Characteristics • Simplest organisms: Very small in size. • Prokaryotic cells have no nucleus. • Lack membrane-bound organelles inside the cell • Have few internal structuresthat are distinguishable under a microscope. • Genetic information is in a circular loop called a plasmid (instead of having chromosomal DNA). • Strong cell walls, resistant to environmental changes. All Prokaryotes are in the Monera kingdom. • Bacteria, • Archaea

7. 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. • .

8. 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

10. 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.

11. 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.

12. 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.

13. 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.

15. 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

16. A few well known Protozoa

17. 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.

18. Brown Algae Diatoms Different types of Algae Green Algae

19. Different Eukaryotic Cells

20. 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.

21. 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. 

22. 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

23. 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. Cellular Differentiation

24. 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).

25. Binary Fission Prokaryotic cells divide through a simple form of division called Binary Fission.

26. Eukaryotic Cell Cycle • The cell cycle consists of • Interphase – normal cell activity • The mitotic phase – cell divsion INTERPHASE (DNA synthesis) Growth G 1 Growth G2 Cell Divsion

27. 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

28. Mitosis • Process of forming identical daughter cells by replicating and dividing the original chromosomes. DNA duplication during interphase Mitosis Diploid Cell

29. Phases of Mitosis Prophase Metaphase • Chromosomes line up along center of cell called the Metaphase Plate • Chromosomes attach to spindle fibers • Spindle & Astral fibers are now clearly visible. • 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 .

30. Anaphase Telophase • Centromeres break up separating chromosome copies • Chromosomes are pulled apart to opposite sides of cell • Spindle & Astral fibers begin to break down • Nuclear envelope forms around both sets of chromosomes. • DNA uncoils. • Spindle & Astral fibers completely disappear.

31. 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.

33. Phases of Meiosis Meiosis I Meiosis II • Prophase I • Leptotene • Zygotene • Pachytene • Diplotene • Diakinesis • Metaphase I • Anaphase I • Telophase I • Prophase II • Metaphase II • Anaohase II • Telophase II Same as Mitosis

34. Prophase I • Coiling and shortening continues as the chromosomes become more condense. • A synapsis (Chiasmata) forms between the pairs, forming a tetrad. • Chromosomes become denser. • The homologous pairs align with one another. • Synaptonemal complexform between homologous pairs. • During this stage, the chromosomes begin to condense and become visible.

35. 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.

36. Meiosis I