General Biology Lecture Notes PDF

29/08/1445 General Biology Lecture (1-2) The Cell College of Applied Sciences Biology Department 03/10/2024 1 ...

29/08/1445 General Biology Lecture (1-2) The Cell College of Applied Sciences Biology Department 03/10/2024 1  29/08/1445 Outline  Biological Organization  The cell Historical overview Cell Theory Types of Cells Eukaryotic Cell structure  Extracellular components  Cell Communication  Metabolism 2  29/08/1445 Biological Organization Living things are highly organized and structured, following a hierarchy from small to large. The biological levels of organization of living things arranged from the simplest to most complex are: atom, molecule, organelle, cells, tissues, organs, organ systems, organisms, populations, communities, ecosystem, and biosphere. The atom is the smallest and most fundamental unit of matter. It consists of a nucleus surrounded by electrons. Atoms form molecules which are chemical structures consisting of at least two atoms held together by one or more chemical bonds. 3  29/08/1445 Biological Organization Many molecules that are biologically important are macromolecules (polymers). A polymer is a large molecule that is made by combining smaller units called monomers. ▪ All living things are made up of four classes of large biological molecules: carbohydrates, lipids, proteins, and nucleic acids, three of which are polymers: – Carbohydrates (include sugars and the polymers of sugars). – Proteins (consists of one or more polypeptides). – Nucleic acids (made of monomers called nucleotides). 4  29/08/1445 Biological Organization Macromolecules can form aggregates within a cell that are surrounded by membranes; these are called organelles such as mitochondria and chloroplasts. All living things are made of cells, and the cell itself is the smallest fundamental unit of structure and function in living organisms. In larger organisms, cells combine to make tissues. Organs are collections of tissues grouped together performing a common function. An organ system is a higher level of organization that consists of functionally related organs. A complex organism contains multiple organ systems with different functions. 5  29/08/1445 Cell Structure & Function 6  29/08/1445 Historical overview The term cell is derived from the latin word ‘Cellula’ which mean a small room. It was first observed by a scientist named ‘Robert Hook’ in the year 1665. He examined sliver of cork and saw “row of empty boxes” and coined the term cell 7  29/08/1445 Cell Theory cell theory is a scientific theory first formulated in the mid-nineteenth century and state that: All living organisms are made up of cells. Cells are the smallest working units of all living organisms. All cells come from preexisting cells through cell division. 8  29/08/1445 Types of Cells There are two distinct types of cells: prokaryotic or eukaryotic. Only organisms of the domains Bacteria and Archaea consist of prokaryotic cells. Protists, fungi, animals, and plants all consist of eukaryotic cells. 9  29/08/1445 Prokaryotic Cells Prokaryotic cells are characterized by having – No nucleus. – DNA in an unbound region called the nucleoid. – No membrane-bound organelles. – Cytoplasm bound by the plasma membrane. 10  29/08/1445 Eukaryotic Cells Eukaryotic cells are characterized by having – DNA in a nucleus that is bounded by a membranous nuclear envelope. – Membrane-bound organelles. – Cytoplasm in the region between the plasma membrane and nucleus. Eukaryotic cells are generally much larger than prokaryotic cells. 11  29/08/1445 Comparing Prokaryotic and Eukaryotic Cells Common features between prokaryotic and eukaryotic cells of: – Plasma membrane. – Semifluid substance called cytoplasm (cytosol). – Chromosomes (carry genes). – Ribosomes (make proteins). 12  29/08/1445 Eukaryotic VS Prokaryotic cells Prokaryotic Cells Eukaryotic Cells Nuclear region (nucleoid) is not Nucleus is surrounded by a enveloped by a nuclear double membrane layer. membrane. Single chromosome More than one chromosome present. are present. Nucleolus is absent. Nucleolus is present. Membrane bound organelles Membrane bound are absent. organelles are present. 13  29/08/1445 Eukaryotic VS Prokaryotic cells Prokaryotic Cells Eukaryotic Cells Cell division by mitosis or Multiplication of cell is by fission meiosis. or budding. Cell walls seen in only plant Cell Walls present, which are cells, which are chemically chemically complex. simpler. Cell type is usually Usually multicellular cells. unicellular. Cell size is 1-10μm Cell size 10 - 100µm. Example: Bacteria, archaea Example: animal cells and plant cells. 14  29/08/1445 Eukaryotic Cell structure the cell membrane The nucleus The cytoplasm Nucleolus Cytoplasmic inclusion Nuclear envelop Matrix Nuclear plasma organelles Cytoplasmic skeleton Chromatin materials15  29/08/1445 1. Plasma Membrane The plasma membrane is the boundary that separates the living cell from its surroundings. Also called Cell membrane Semi-permeable: allows nutrients in and waste products out Plasma membrane is made of a double layer of phospholipids. 16  29/08/1445 Cell Membrane structure The currently accepted model for the structure of the plasma membrane, called the fluid mosaic model According to this model the plasma membrane is a mosaic of components—primarily, phospholipids, cholesterol, and proteins—that move freely and fluidly in the plane of the membrane. Phospholipids are the most abundant lipid in the plasma membrane. Phospholipids are amphipathic molecules, containing hydrophobic and hydrophilic regions. 17  29/08/1445 Cell Membrane functions 1. The main function of plasma membrane is that it acts as a physical barrier between the external environment and the inner cell organelles. 2. Plays a vital role in protecting the interior of the cell by allowing only selected substances into the cell and keeping other substances out. 3. Facilitating the communication and signaling between the cells. 4. Maintaining the shape of the cell because it serves as a base of attachment for the cytoskeleton in some organisms. 18