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Chapter 2

Chapter 2 Cell Physiology (Kine 2011).pdf

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Department
Kinesiology & Health Science
Course Code
KINE 2011
Professor
Gillian Wu

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Chapter  2  Cell  Physiology  (Kine  2011)     -Cells are about 10 -20 micrometers in size -Three people from Netherlands Hans Lipphershey , Hans and Zachrias Janssesn (who were father and son) are given credit for inventing microscope. -Larger species have more cells, NOT BIGGER cells. -Cell size is the same for whale and humming bird. -Electron microscopes 1000X more powerful than Light microscopes Overview of Cell Structure -There are trillions of cells in human body but 200 different types of cells according to structure and function. -All muscle cells contain multiple nuclei (multinucleated), cytosol, ribosomes, and mitochondria which is common to many cells - Muscle cells slow -twitch (type 1) and fast twitch (type 2) -Most cells have major 3 subdivisions such as (i) plasma membrane: which encloses the cell (ii) nucleus: which contains the cells genetic material (iii) cytoplasm: the portion of the cell’s interior not occupied by the nucleus Plasma Membrane - plasma membrane: thin membraneous structure which encloses the cell -Oily and separates ICF(interior cellular fluid) from ECF ( extra -cellular fluid) -is a barrier, and also helps control the entry of food and other needed supplies and guards against unwated traffic in and out of the cell. Nucleus - Two major parts of cells interior are (i) Nucleus (ii) Cytoplasm -Nucleaus: contains the genetic information Structure: contains double layered membrane called nuclear envelope which is peirved by many nuclear pores which allow traffic to move between nuc leaus and cytoplasm. - Two main purpose (i) Directs protein synthesis (ii)Serves as a genetic blueprint during cell replication Cytoplasm - Cytoplasm: the portion of the cell’s interior not occupied by the nucleus but includes ORGANELLES. - Cytoplasm contains membrane enclosed structures called organelles ( little organs) Chapter  2  Cell  Physiology  (Kine  2011)     -50% of the cell vol is occupied by organelles - 6 main types of organelles are: (i) Endoplasmic Reticulum (ii)Golgi complex (iii) Lysosomes (iv)Peroxisomes (v) Mitochondria (vi) Vaults - Cytosol: the remainder of the cytoplasm not occupied by the organelles consists of the cytosol (“cell liquid”) -Cytosol is made up of a semiliquid, gel like mass laced with an elaborate protein network known as the cytoskeleton. Intercellular Fluid (ICF) : includes all the fluid contained within the plasma membrane, including the cytosol, organelles, and the nucleus. (i) Endoplasmic Reticulum Structure: Extensive contionsou membranous network of fluid -filled tubules and flattened sacs partially studded with ribosomes Function: Forms new cell membrane and other cell components and manufactures products for secretion ER is a continuous organelle with many interconnected channels. The ROUGH ER - outer surface with dark studded protein -assemblers (workbenches) called RIBOSOMES due to that it has rough appearance. -projects out from the smooth ER -Not permanently attached to ER -Rough ER works with Go lgi Complex to assemble new proteins and get them into proper destinations -Along with Ribosomes also has new proteins which are released in the ER lumen. The two main purpose of these proteins are (i) some proteins are destined for export to the cell’ s exterior as secretory products , such as protein hormones or enzymes ( all enzymes are proteins). (ii) Other proteins are transported to sites within the cell for use in constructing new cellular membrane ( plasma or new organelle mem) Q How do the newly synthesized molecules witin the ER lumen get to their destinations at other sites inside the cells or to the outside of the cell if they cannot pass out of the ER membrane? Chapter  2  Cell  Physiology  (Kine  2011)     Ans: They do with action of the smooth Endoplasmic Reticulum ( the transporter) The SMOOTH ER -Structure: is smooth no ribosomes, mesh of interconnected tubes. - Function: serves as a central packaging and discharge site for molecules to be transported from. -Newly synthesized proteins go from rough ER to smooth ER . Portion so fht s mooth ER then bud off forming transport vesicles (which contain many new molecules encolosed in a spherical membrane derived from the smooth ER. ) vesicle: fluid filled membrane enclosed intra-cellular cargo container Review page 26 for secretion process for proteins synthesized by ER. Smooth ER helps in lipid metabolism -It has enzymes for synthesis of lipids -In liver cells, smooth ER contains enzymes for detoxifying harmful substances produced witin the body metabolism or any other substances. -Muscles have an elaborate but modified smooth ER known as sarcoplasmic reticulum which stores calcium. -Calcium important for myoosin attachment to the actin which is why there is muscle contraction and movement. Golgi Complex -Structure: Sets of stacked, flattened membranous sacs -Function: Modifies packages and distributes newly synthesized proteins -Cells which are highly specialized for protein secretion have hundereds of stacks of Golgi. Lysosomes and Endocytosis -Cell contains about 300 Lysosomes. -Structure: Membranous sacs containing hydrolytic enzymes.(Most commonly small about 0.2 to 0.5um) -Functions: Serves as digestive system of the cell, destroying foreign substances and cellular debris. -Small bodies within the cell that breakdown organic m olecules. -Lysosomes serve as the “intracellular digestive system.” Endocytosis is a process by which cells absorb molecules (such as proteins) by engulfing them Endocytosis has three ways: (i) Phagocytosis ( very few cells) (iii) Pinocytosis ( most cells) (iii) Receptor mediated (also some cells) Chapter  2  Cell  Physiology  (Kine  2011)     Phagocytosis (cell eating) - Extracellular material which is to be attacked by the Lysosomal enzymes is brought in by the process of Phagocytosis ( a type of endocytosis) -large multimolecular particles are internalized -only a few cells are capable of doing that -White blood cells are an example and when there is an bacterium or other particle, it extends its pseudopods (“ false feet”) that completely surround or engulf the particle or trap it within the vesicle. -The engulfed material is broken down into amino acids, glucose, and fatty acids for the cell to use. Pinocytosis (cell drinking) -No pseudopods are formed - In the process of pinocytosis the plasma membrane froms an invagination. -Any substance is found within the area of invagination is brought into the cell. -The plasma membrane seals at the surface of the pouch , trapping the contents in a small , intracellular endocytotic vesicle. -Dynamin: protein molecule responsible for pinching off an endocytotic vesicle, forms rings that wrap around and writing the neck of the pouch severing the vesicle from the surface membrane. Receptor mediated (also some cells) -Highly selective process that e nables cells to import specific large molecules from the environment. -Cholesterol complexes, Vitamin B12, the hormone insulin and iron are examples of substances taken into cells by this process. -HIV, AIDS, also can gain entry via this process Chapter  2  Cell  Physiology  (Kine  2011)     Animation link: http://www.northland.cc.mn.us/biology/Biology1111/animations/transport1.html -Lysosomes can also fuse with aged or damaged organelles to remove these useless parts of the cell. This selective digestion is known as autophagy “self eating” . -If they accumulate could cause disease such as Tay-Sachs disease characterized by abnormal accumulation of complex molecules found in nerve cells. Peroxisomes and Detoxification -Several hundred peroxisomes are present 1 Size is almost /3to ½ of the lysosomes. Structure: Membranous sacs containing oxidative enzymes Function: Perform detoxification activities UNLIKE LYSOSOME THEY DON’T HAVE HYDROLYTIC ENZYMES but they have OXIDATIVE ENZYMES. -Oxidative enzyme: use Oxygen to take out hydrogen from certain molecules which helps detoxify some wastes in the cell. ( ie alcohol) -Major product generated in the peroxisomes is hydrogen peroxide (H O ). 2 2 -Catalase: anti-oxidant enzyme which decomposes potent H O in2o 2 O and 2. Mitochondria and ATP Production -Cells contain few hundereds to several thousands mitochondria -Structure: Oval shaped bodies enclosed by two membranes with the inner mem folded into cristae that project into interior matrix. -about 1-10 micrometer -Descendants of bacteria -Has its own DNA -Diseases related to mitochondria include Nervous-system and muscle diseases such as Kearns-Sayre syndrome. Function: Acts as energy organelles, extracts energy from the food , major sites for ATP production, contains enzymes for ETC and Kreb(Citric) cycle. Chapter  2  Cell  Physiology  (Kine  2011)     -Generate about 90% that we need to survive. -Cristae: contains crucial proteins for converting energy from food to usable form (ETC proteins) -Inner membrane: folds increase the surface area for housing the important proteins. -Matrix: contains concentrated mix of hundreds of diff dissolved enzymes ( the t ricarboxylic acid cycle enzymes) -Source of energy for the body is the chemical energy from the carbon bonds of ingested food. -But our body cannot use this energy directly and has to be converted into Adenosine- Triphosphate (ATP). -ATP is the currency of the body -ATP is used it makes Adenosine-Diphosphate -ATP à (Splitting) ADP + Pi + energy for the use by the cell -ATP is generated in most cells using the following 3 reactions to generate energy (i) Glycolysis: happens in cytosol(fluid) (also valid answer is cytoplasm(space)) -involves 10 steps -breaks down simple 6 -carbon sugar molecule into TWO 3-carbon pyruivic molecules. -Energy from the broken chemical bonds is used to convert ADP to ATP. -Not that much efficient , only 2 ATP are formed -Related to McArdle disease ( causes cramp -like pains) when the people cannot break down glycogen to glucose -Anaerobic (doesn’t need oxygen) (ii) Kreb Cycle (Tricarboxylic Acid Cycle) -occurs in the mitochondria matrix -Pyruvic acid enters mitochondria matrix via protein monocarboxylate transporter -Pyruvic acid is catalyzed by the enzyme Pyruvate Dehydrogenase (PDH) -Pyruvic acid from glycolysis is converted into Acetyla Coa which enters the tricarboxylic acid cycle also known as the Kreb or Citric cycle. -This process consists of 8 different biochemical rxns directed by the enzymes of mitochondrial matrix -It also prepares and generates hydrogen carrier molecules for entry into the ELECTRON TRANSPORT CHAIN. -Acetyl CoA ( 2-C molecule) combines with Oxaloacetic acid (4 -C molecule) to form a (6 -C molecule) called citric acid which is where the name comes from the Citric acid cycle. Steps of the process: 1. The citric acid cycle begins when Coenzyme A transfers its 2 -carbon acetyl group to the 4- carbon compound oxaloacetate to form the 6 -carbon molecule citrate (see Fig. 18). 2.
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