Al Safwa University College Medical Biology (Theory) 2024-2025 PDF

Lec. 3 Al Safwa University College Medical Biology (Theory) 2024-2025 st st (1 Stage 1 Semester) Cell (Cont..) Prokaryotic and Eukaryotic Cells Cells are of tw...

Lec. 3 Al Safwa University College Medical Biology (Theory) 2024-2025 st st (1 Stage 1 Semester) Cell (Cont..) Prokaryotic and Eukaryotic Cells Cells are of two types, eukaryotic, which contain a nucleus, and prokaryotic, which do not. Prokaryotes are single-celled organisms, while eukaryotes can be either single-celled or multicellular. The distinction between prokaryotes and eukaryotes is considered the most important distinction among groups of organisms. Eukaryotic cells contain membrane - bound organelles, such as the nucleus, while prokaryotic cells do not. Comparison between prokaryotic and eukaryotic cells. Similarities:  They both have DNA as their genetic material.  They are both membrane bound.  They both have ribosomes.  They have similar basic metabolism. Differences:  Eukaryotes have a nucleus, while prokaryotes do not.  Eukaryotes have membrane-bound organelles, while prokaryotes do not.  Eukaryotic cells are, on average, ten times the size of prokaryotic cells.  The DNA of eukaryotes is much more complex and therefore much more extensive than the DNA of prokaryotes.  Prokaryotes have a cell wall composed of peptidoglycan, a single large polymer of amino acids and sugar. Many types of eukaryotic cells also have cell walls, but none made of peptidoglycan.  The DNA of prokaryotes floats freely around the cell; the DNA of eukaryotes is held within its nucleus and associated with histones (proteins).  Eukaryotes undergo mitosis; prokaryotes divide by binary fission (simple cell division).  Comparison of features of prokaryotic and eukaryotic cells Characteristics Prokaryotes Eukaryotes Typical size Small cells ( ~ 1-10 μm) Large cells (~ 10-100 μm) Organization Always single cells Often multicellular, single cell Nucleus absent Present Nucleulus absent Present Membrane bounded absent Present cell organelles DNA is single circular More than one liner DNA chromosome chromosome Ribosomes small (70 S) large (80 S) Mitosis (normal cells binary fission or budding Cell division replication) , meiosis (gamete (no mitosis) production) Reproduction is always Reproduction Rep. is asexual or sexual asexual Example: human, animals, and Typical organism Example: bacteria plants Cell Number Unicellular organisms – Organisms with single cell, capable of independent existence and carries all functions like digestion, excretion, respiration, growth & reproduction (Acellular). Examples, Amoeba, Euglena Multicellular organisms – Organisms with more than one cell, Cells in multicellular organisms vary in size & shape depending on function. Cell Shape Cell Shapes and Sizes The shape of the animal eukaryotic cells: About 200 types of cells in human body with varied shapes:  Squamous (Flattened) —thin, flat, scaly (Squamous epithelial cells in bowman`s capsule)  Cuboidal—squares-looking (Epithelial cells of glands)  Columnar—taller than wide (Absorptive epithelial cells in stomach and intestine)  Polygonal—irregularly angular shapes, multiple sides (Liver cells)  Stellate—star-like, Tree shaped (Multipolar neurons in spinal cord)  Spheroid to ovoid, Oval/spherical shaped—round to oval (Ova)  Discoid—disc-shaped (RBC)  Fusiform—thick in middle, tapered toward the ends (smooth muscles)  Fibrous—thread-like (skeletal muscles). Note: A cell’s shape can appear different if viewed in a different type of section (longitudinal vs. cross section). The shape of the prokaryotic cells (Bacteria): Spherical shaped (coccus) Rod/cylindrical shaped (bacillus) 2 Spiral shaped (spirillum/spirochete/vibrio) Bacteria (1.25 μ diameter) (0.15-15 μ length) in size.  Animal Cell Shapes  Bacterial Shapes Cell Size Human cell size: Most cells about 10–15 micrometers (μm) in diameter. Egg cells (very large) 100 μm diameter Some nerve cells over 1 meter long Size: varies from few microns (1 cm= 10 mm; 1mm= 1000μm). 3 Cell Growth and metabolism Growth means an increase in the size of the cell as a result of increasing the amount of protoplasm.  Reproduction of a Prokaryotic cells is achieved by binary fission, Reproduction of a Eukaryotic cells is achieved by division of a mature cell either by mitosis in somatic cells or meiosis in a sex cells.  Metabolism: is a chemical process of a living cell by which nutrient material is effected, and it is two types:  Catabolism: this process involves the breakdown of the food material (protoplasm of other cells) brought into the cell. Energy will be released by this process to be used by the cell in different activities  Anabolism: in this process energy released by catabolism is utilized by the cell to produce materials that are retained or released from cell 4