Human Anatomy and Physiology Lecture II - Cell PDF

**Human Anatomy and Physiology** Lecture II **Cell** - Is the basic living unit of all organism. It is a complex, highly organized living structure in spite of the size. Within the cells are specialized structures called organelle that performs specific functions. The type of cell d...

**Human Anatomy and Physiology** Lecture II **Cell** - Is the basic living unit of all organism. It is a complex, highly organized living structure in spite of the size. Within the cells are specialized structures called organelle that performs specific functions. The type of cell determine the form and function of the human body. Human body is composed of trillions of cells. **Function of the cells** - **Cell metabolism and energy use**- the chemical reactions that occur within the cells are called cell metabolism. Energy released during metabolism is used for cell activities such as synthesis of new molecules, muscle contraction and maintenance of body temperature. - **Synthesis of molecule** -- various molecules such as proteins, nucleic acids and liids are all produced by cells. The structural and functional characteristics of cell are determined by the types of molecules they produced. - **Communication** -- cells produce and receive chemical and electrical signals that allow them to communicate with one another - **Reproduction and inheritance** -- each cell contain a copy of the genetic information of the individual. Specialized cells such as sperm and oocyte transmit the genetic information to the next generation. **Cell Parts** - **Cell Membrane** - Is the outermost component of the cell. It encloses the cytoplasm and for the boundary between material inside the cell and outside the cell. It likewise support the cell content and acts as selective barrier that determines what moves in and out of the cell that play a major role in cell communication. Extracellular substance are substance outside the cell and Intracellular substance are substance inside the cell. Made up of 2 major types of molecules- Phospholipids and proteins. Other component are cholesterol and carbohydrates. The arrangement of the molecules give rise to the fluid mosaic model. Phospholipids form a double layer where the Phosphate containing ends are hydrophilic (water lover) polar end which faces the extracellular and intracellular area of the cell. The phospholipid end that contains the fatty acids are the non polar ends or Hydrophobic (water fearing) thus facing away the from the fluid on either side of the membrane. The layer has fluid quality and are not stationary but able to move. Cholesterol provide added strength to the cell membrane. Proteins floats in the bilayer and may extend to either side of the membrane with carbohydrates that may be bound to proteins modifying their functions. Proteins may function as membrane channels that are involved with movement of substances through the cell membrane. - **Organelles** **Nucleus** -- is a large organelle usually located near the center of the cell. All cells has nucleus except the mature RBC. It is bounded by the nuclear envelope consist of outer and inner membrane with narrow space forming ***nuclear pores*** through materials can pass through in and out of the nucleus. It contain 23 pairs of chromosomes consists of DNA and proteins. **Ribosomes** -- are the site of protein synthesis. May be attached to other organelle such as the endoplasmic reticulum. Free ribosomes are those not attached to ER **Rough and Smooth Endoplasmic Reticulum** -- is a series of membranes forming sacs and tubules that extends from the outer nuclear membrane into the cytoplasm. ***Rough ER** --* are those with ribosomes attached to it that indicates high protein synthesis for export outside of the cells ***Smooth ER*** -- without ribosome attached and is the site for lipid synthesis - **Golgi apparatus** -- also called Golgi Complex. Consists of closely packed stacks of curved, membrane bound sacs that collect, modifies, packages and distributes proteins and lipids produced by the ER. - **Secretory Vesicle** -- is a small, membrane bound sac that transport or stores material within cells. It pinch off from the Golgi apparatus and move to the cell membrane. It fuses then to the cell membrane and the contents are released to the exterior of the cell. In many cells, secretory vesicles accumulates at the cytoplasm and are released once they receive a signal. Example is Neurotransmitter a substance that is released by the Nerve cell to communicate with other cells. - **Lysosomes** -- are membrane bound vesicles formed from the Golgi Apparatus. They contain enzymes that function for intracellular digestive system. It contains enzymes that breakdown materials in the endocytotic vesicle. Example is WBC that phagocytize the bacteria which is then destroyed within the lysosomes. **Peroxisomes** -- are small membrane bound vesicle containing enzymes that break down fatty acids, amino acids, and hydrogen peroxide. H2O2 is broken down by the enzymes in peroxisomes to water and O2. These are more concentrated in organs involve in detoxification like kidneys and liver. - **Mitochondria** -- are small organelles with inner and outer membranes separated by space. The outer membrane have smooth contour and the inner membrane have numerous folds called cristae which project to the interior of the mitochondria. The inner membrane has the mitochondrial matrix and contains enzymes and mitochondrial DNA. The mitochondria is the major site of adenosine triphosphate (ATP) production and the main energy currency of the cell that carry out aerobic respiration, a series of chemical reactions that require O2 to breakdown food molecules to produce ATP. - **Cytoskeleton** -- as the internal framework of the cell composed mainly of protein structures that support the cell, hold organelles in place and enable the cell to change shape. These Microtubules, Microfilaments and Intermediate Filaments. **Microtubules** -- are hollow structure formed from protein subunits that perform variety of rules including helping to support cytoplasm of the cell, assisting in cell division, and forming essential components of certain organelles such as cilia and flagella. **Microfilaments** -- are small fibrils formed from protein subunits that structurally support the cytoplasm, determining cell shape and are involve in cell movement. This enable the cell to shorten or contract. **Intermediate filaments** -- are fibrils formed from protein sub unit that are smaller in diameter than microtubules but are larger in diameter than microfilaments. They provide mechanical support to the cell. Example are keratin, a protein associated with skin cells. - **Centrioles** -- these are small cylindrical organelles composed of microtubules that forms the centrosomes. They play an important role in cell division. - **Cilia** -- is a form of cellular appendage that project from the surface of the cell. They are cylindrical structure that composed of microtubule that lines numerously in the respiratory tract that aids in the transport of mucus or dust particle away from the lungs. - **Flagella** -- have structure similar with cilia but are much longer usually occur in one cell like the sperm cell that aids in cellular locomotion. - **Microvilli** -- are specialized extensions of the cell membrane that are supported by microfilaments but do not move like the cilia and flagella. They line abundantly in the small intestines, kidneys and other areas involve in absorption of nutrients and substances. **Whole Cell Activity** - Refers to the type of cell activity that is determined by the protein that it produces. This in turn is determined by the genetic information that is present in the nucleus of that particular cell. To understand fully cellular activity it is best that we understand the connection of Genes and Proteins that each cell posses. As we have learned from the start of our study, each humans begins life as a single cell. Through cell division and cell differentiation the cells that made up the human body are formed. This happened through the various processes of protein synthesis in cells which were determined by the genetic material, which is the DNA that is present in the nucleus of the cell. The following are the basic concepts of Genetics - **Gene Expression** -- is the process by which DNA that contains the genetic information directs protein synthesis. The protein produced in a cell includes those that serve as structural component inside the cell, proteins secreted to the outside of the cell, and the enzymes that regulate chemical reactions in the cell. - **Gene** -- is a sequence of nucleotides that provides a chemical set of instructions ( like a recipe) for making a specific proteins. It is contained in the DNA. - **DNA** -- is a molecule consist of a nucleotides joined together to form two nucleotide strands. The two strands are connected and resemble a ladder that is twisted around its long axis. - **2 steps of Gene expression;** - ***Transcription*** -- is the first step in gene expression that takes place inside the nucleus. During this stage the double stranded DNA separates and the DNA Nucleotide of the gene, pair with the RNA nucleotide forming the mRNA. The information in mRNA is carried in group of three nucleotide called ***Codons*** which specify a particular amino acid. - ***Translation*** -- is the synthesis of proteins based on the information in mRNA. It occurs in the Ribosomes. The mRNA molecules produced by transcription pass through the nuclear pores to the Ribosomes. Ribosomes are consist of small and large subunits which combine with mRNA during translation. - **Cell Cycle** -- cell cycle is a process by which a cell undergoes cell growth and development through cell division and then follows a process of cellular replacement and repair. There are two process -- the non-dividing phase called ***Interphase*** and ***Cell division.*** **Interphase** -- this refers to the time where the cell spends most of its life performing its normal function. During this phase the DNA located in the chromosome in the cell's nucleus is replicated. **Cell division**- is the formation of daughter cells from a single parent cell. The new cells are necessary for growth and tissue repair are formed through Mitosis, and Meiosis where the sex cells necessary for reproduction is formed. Each cell of the human body except the sex cells (egg and sperm) contains 46 diploid chromosomes and are organized to form 23 pairs. Sex cells only have half of the number of chromosomes. Of the 23 pairs, 1 pair is the sex chromosome that determine the sex of the individual which consists of either 2 XX (Female) or 2 XY ( male). The remaining 22 pairs are called autosomes that determine most of the other characteristics. **Mitosis** -- the process of cell division for most cell of the body except those of the sex cells. In this process, a parent cell divides to form 2 daughter cells with the same amount of and type of DNA as the parent cell. There are 4 stages -- Prophase, Metaphase, Anaphase and Telophase. - **Apoptosis** -- also called programmed cell death. Is a normal process by which cell numbers within various tissues are adjusted and controlled. Examples of apoptosis are the removal of excess tissues between fingers and toes in a developing fetus, elimination of excess cells to maintain a constant number of cells within the tissue and elimination of cells that are infected with virus or cancer cells. It is regulated by specific genes. The proteins coded for those genes initiate events within the cell that ultimately lead to cells death. This is done through fragmentation of the nucleus and of the cell. **Cellular aspect of aging** - Majority of the hypotheses that attempt to explain how aging occurs concentrate on molecules within the cell, such as lipids, proteins and nucleic acids. 35% of the factors that affects aging are genetics. - **Cellular clock** -- after a certain passage of time or a certain number of cell divisions, results in the death of a given cell lines. - **Death genes**- turn on late in life or sometimes prematurely causing cells to deteriorate and die. - **DNA Damage** -- through time DNA is damaged resulting in cell degeneration and death. - **Free radicals** -- these are atoms or molecules with unpaired electron that may cause direct damage to DNA resulting in cellular dysfunction leading to cellular death. High caloric intake is one major source of free radicals. - **Mitochondrial damage** -- this refers to mitochondrial DNA damage from exposures to free radicals that may result in loss of protein critical to mitochondrial function particularly on the ATP production leading to loss of energy critical to cellular function and ultimately cell death.