Lec. 1: Cell Biology Part 2 (2021/2022) PDF

Lec. 1:Cell biology part -2 By: Dr. Zainab O. al-Aloosh 2021/2022  b. Vesicle Transport ▰ Some molecules or particles are just too large to pass through the plasma membrane or to move through a transport protein. So cells use two other active transport pro...

Lec. 1:Cell biology part -2 By: Dr. Zainab O. al-Aloosh 2021/2022  b. Vesicle Transport ▰ Some molecules or particles are just too large to pass through the plasma membrane or to move through a transport protein. So cells use two other active transport processes to move these macromolecules (large molecules) into or out of the cell. ▰ Vesicles or other bodies in the cytoplasm move macromolecules or large particles across the plasma membrane.There are two types of transport, endocytosis and exocytosis. Both processes are active transport processes, requiring energy. 2 ▰ Endocytosis is the process of capturing a substance or particle from outside the cell by engulfing it with the cell membrane. The membrane folds over the substance and it becomes completely enclosed by the membrane. At this point a membrane-bound sac, or vesicle, pinches off and moves the substance into the cytosol. There are two main kinds of endocytosis: 3 ▰ Pinocytosis (‘cell drinking’) This is the uptake of large molecules (DNA, protein) from solution, by a form of endocytosis – the vesicles formed are minute and short-lived. ▰ Phagocytosis (‘cell eating’) This is the uptake of solid particles by a cell e.g., Phagocytes engulfing bacteria. 4 ▰ Exocytosis describes the process of vesicles fusing with the plasma membrane and releasing their contents to the outside of the cell. ▰ Exocytosis occurs when a cell produces substances for export, such as a protein, or when the cell is getting rid of a waste product or a toxin. 5 6  The Cell Cycle ▰ The cell cycle, is the series of events that leads to duplication and division of a cell. ▰ Division cycle consists of 4 coordinated processes:(1) cell growth,(2) DNA replication, (3)distribution of the duplicated chromosomes ,(4) cell division. ▰ The alternation between mitosis and interphase called cell cycle. ▰ Mitosis(4 stages): (1)Prophase (2) Metaphase (3) Anaphase(4) Telophase 7 8 ▰ Interphase, is itself divided into three phases ▰ (1). G1 (Presynthesis) ▰ (2). S (DNA synthesis) ▰ (3). G2 (Post DNA duplication) ▰ The cell cycle divided into four periods, G1, S, G2 and mitosis (M) 9 ▰ G1(Gap1): The first gap in the normal cell cycle is called G1 and is the period when the necessary proteins for DNA replication are synthesized. The cell grow in size and the cellular organelles increase in number, the ▰ cell is metabolically active & continuously grows but does not replicate its DNA. 10 ▰ (S) is referred as synthesis phase when DNA synthesis. During duplication, each chromosome doubles to produce identical sister chromatids, and also centrioles replicate take place. ▰ G2 (Gap2) is the internal between chromosome duplication and the beginning of mitosis, during which cell growth continues and proteins are synthesized in preparation for mitosis. 11 ▰ The duration of the cell cycle phases varies considerably in different kinds of cells. ▰ Cell cycle activities may be temporarily or permanently suspended in a G0 phase. ▰ Some cells, such as skin cells, divide continuously throughout the life of the organism. Other cells, such as skeletal muscle cells and nerve cells, are arrested in the G1 stage. Cardiac muscle cells are arrested in the G2- stage. 12 ▰ The coordination between different phases of cell cycle is dependent on a system of checkpoints and feedback controls that prevent entry into the next phase of the cell cycle until the events of the preceding phase have been completed. Several cell cycle checkpoints function to ensure that incomplete or damaged chromosome are not replicated and passed on to the daughter cells. 13 ▰ Thank you for listening 14