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UNDERSTANDING STRUCTURE AND FUNCTION It appears that life first emerged at least 3.8 billion years ago, approximately 750 million years after Earth was.

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Presentation on theme: "UNDERSTANDING STRUCTURE AND FUNCTION It appears that life first emerged at least 3.8 billion years ago, approximately 750 million years after Earth was."— Presentation transcript:

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2 UNDERSTANDING STRUCTURE AND FUNCTION

3 It appears that life first emerged at least 3.8 billion years ago, approximately 750 million years after Earth was formed

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5 Simple Biological Molecules Were Formed Under Prebiotic Conditions During the first billion years on earth, there was little free O 2 and no O 3 to absorb UV radiation from the sun. Simple organic molecules were formed under such conditions. During the first billion years on earth, there was little free O 2 and no O 3 to absorb UV radiation from the sun. Simple organic molecules were formed under such conditions. Laboratory experiments simulating the primitive earth have confirmed that organic molecules could have been formed Laboratory experiments simulating the primitive earth have confirmed that organic molecules could have been formed When gases such as CO 2, CH 4, NH 3, and H 2 were heated with water and energized by electrical discharge or by UV radiation, they reacted and formed small organic molecules. When gases such as CO 2, CH 4, NH 3, and H 2 were heated with water and energized by electrical discharge or by UV radiation, they reacted and formed small organic molecules. More importantly, the organic molecules (amino acids, nucleotides, sugars, and fatty acids) were also generated. More importantly, the organic molecules (amino acids, nucleotides, sugars, and fatty acids) were also generated. Next step in evolution was the formation of macromolecules through spontaneous polymerization and capable of reproduction and further evolution Next step in evolution was the formation of macromolecules through spontaneous polymerization and capable of reproduction and further evolution Stanley Miller’s experiment in 1950 Stanley Miller’s experiment in 1950

6 Cells in culture, stained for keratin (red) and DNA (green).stainedkeratinDNA

7 What is Cell? Cell is the structural and functional unit of living organisms.

8 What is cell Cell is the basic unit of organization of all living matter. Cell is the basic unit of organization of all living matter. Within a selective and retentive semipermeable membrane, it contains a complete set of different kinds of units necessary for own growth and reproduction from simple nutrients Within a selective and retentive semipermeable membrane, it contains a complete set of different kinds of units necessary for own growth and reproduction from simple nutrients

9 Every organism consists of cells; Every organism consists of cells; from the simplest single organism -the bacterium to the most complex multicellular organism. from the simplest single organism -the bacterium to the most complex multicellular organism. Basic Properties of Cells Basic Properties of Cells –Cells are highly complex and organized. –Cells possess a genetic program –Cells are capable of reproducing. –Cells acquire and utilize energy. –Cells engage in numerous mechanical activities. –Cells are able to respond to stimuli. –Cells are capable of self-regulation.

10 Eukaryotes have a nucleus and many other organelles with specialized function

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12 Living cells are divided into types based on internal complexity. Living cells are divided into types based on internal complexity. TYPES OF CELLS Prokaryotic Eukaryotic

13 1.no nuclear envelope 2.little noncoding DNA 3.no chromatin 4.ribosome subunits 70S 5.lack of cellular organelles 6.single circular chromosome 7.peptidoglycan cell wall 1.nuclear envelope 2.great deal of noncoding DNA 3.chromatin & remodelers 4.ribosome subunits 80S 5.cellular organelles 6.multiple linear chromosomes 7.no peptidoglycan Prokaryotes Eukaryotes

14 The Cell Membrane The cell membrane functions as a semi- permeable barrier, allowing a very few molecules across it. The cell membrane functions as a semi- permeable barrier, allowing a very few molecules across it. Consists mainly of lipid bilayer with associated protein. Consists mainly of lipid bilayer with associated protein. Ref:Basic Concept of Cell Biology and Histology Ref:Basic Concept of Cell Biology and Histology Author: McKenzie Author: McKenzie

15 The cell membrane is about 7.5 nm thick The cell membrane is about 7.5 nm thick MEMBRANE STRUCTURE –Lipids + Proteins + Carbohydrates molecules FUNCTIONS To control selective entrance and exit of materials. This allows the cell to maintain constant internal environment To control selective entrance and exit of materials. This allows the cell to maintain constant internal environment Transport of small molecules like, water, O 2, CO 2 across the plasma membrane Transport of small molecules like, water, O 2, CO 2 across the plasma membrane

16 The lipid bilayer is freely permeable to small, lipid soluble, nonpolar molecule but is impermeable to charged ions. Molecular structure: The lipid bilayer is composed of phospholipid, glycolipid and chclesterol. Phospholipids are amphipathic, consisting of one polar (hydrophilic) head and two nonpolar (hydrophobic) fatty acid tail.

17 The polar head of each molecule face the membrane surface, whereas the tails project into the interior of the membrane. The tails of the two leaflets face each other, forming weak bond that attach the leaflets to each other. Glycolipids are restricted to the outer leaflets. Polar carbohydrate residues of glycolipids extend from the outer leaflet into the extracellular space and form part of the glycocalyx.

18 Cholesterol constitutes 2% of lipids helps maintain the structural integrity of the membrane.

19 The Cell Membrane Integral proteins Integral proteins Span the entire plasma membrane and function as membrane receptor & transport proteins. known as gateway proteins. Span the entire plasma membrane and function as membrane receptor & transport proteins. known as gateway proteins.

20 CARBOHYDRATES CARBOHYDRATES –Always located external to cell –Linked to proteins as glycoproteins; and to lipids as glycolipids

21 The Cell Membrane Cholesterol is another important component of cell membranes embedded in the hydrophobic areas of the inner (tail- tail) region. Cholesterol is another important component of cell membranes embedded in the hydrophobic areas of the inner (tail- tail) region. Most bacterial cell membranes do not contain cholesterol Most bacterial cell membranes do not contain cholesterol

22 The Cell Membrane Cell membranes Cell membranes – The membrane allows materials needed for life processes to pass through and also gets rid of waste materials left over from these processes

23 TRANSPORT OF SUBSTANCES THROUGH THE CELL MEMBRANE 1. Passive transport A. Simple diffusion B. Faciliated diffusion 2. Active transport

24 Passive transport A. SIMPLE DIFFUSION Transports small nonpolar molecules, O 2, N 2 small uncharged polar molecules-water, CO 2 Transports small nonpolar molecules, O 2, N 2 small uncharged polar molecules-water, CO 2 - No Chemical Energy used - No Chemical Energy used Properties Of Simple Diffusion: Properties Of Simple Diffusion: –Direction (High to Low) –Equilibrium (Equal concentrations)

25 B. FACILIATED DIFFUSION Faster than simple diffusion and occurs via ion channels and carrier proteins. Ions and large polar molecules are transported. Faster than simple diffusion and occurs via ion channels and carrier proteins. Ions and large polar molecules are transported. Usually the systems reserved for polar and relatively large molecules but transport smaller ions too – Na +, K +, Ca 2+, H + Usually the systems reserved for polar and relatively large molecules but transport smaller ions too – Na +, K +, Ca 2+, H + System uses protein carriers to carry the solute across the membrane. System uses protein carriers to carry the solute across the membrane.

26 FACILITATED DIFFUSION Higher to Lower (Equilibrium) Higher to Lower (Equilibrium) No Chemical Energy used No Chemical Energy used Major route for Glucose Major route for Glucose ACTIVE TRANSPORT Lower to Higher (No Equilibrium) Lower to Higher (No Equilibrium) Metabolic Energy used Metabolic Energy used Ions, Polar Molecules Ions, Polar Molecules FACILITATED DIFFUSIONACTIVE TRANSPORT FACILITATED DIFFUSION vs ACTIVE TRANSPORT

27 Passive and active transport compared. (A) Passive transport down an electrochemical gradient occurs spontaneously, either by simple diffusion through the lipid bilayer or by facilitated diffusion through channels and passive carriers. By contrast, active transport requires an input of metabolic energy and is always mediated by carriers that harvest metabolic energy to pump the solute against its electrochemical gradient. (A) Passive transport down an electrochemical gradient occurs spontaneously, either by simple diffusion through the lipid bilayer or by facilitated diffusion through channels and passive carriers. By contrast, active transport requires an input of metabolic energy and is always mediated by carriers that harvest metabolic energy to pump the solute against its electrochemical gradient. (B) An electrochemical gradient combines the membrane potential and the concentration gradient, which can work additively to increase the driving force on an ion across the membrane (middle) or can work against each other (right). (B) An electrochemical gradient combines the membrane potential and the concentration gradient, which can work additively to increase the driving force on an ion across the membrane (middle) or can work against each other (right).

28 Permeability of phospholipid bilayers

29 Gases, hydrophobic molecules, and small polar uncharged molecules can diffuse through phospholipid bilayers. Larger polar molecules and charged molecules cannot. Gases, hydrophobic molecules, and small polar uncharged molecules can diffuse through phospholipid bilayers. Larger polar molecules and charged molecules cannot. Transport of small molecules

30 During passive diffusion, a molecule simply dissolves in the phospholipid bilayer and diffuses across it During passive diffusion, a molecule simply dissolves in the phospholipid bilayer and diffuses across it then dissolves in the aqueous solution at the other side of the membrane then dissolves in the aqueous solution at the other side of the membrane the direction of transport is determined simply by the relative concentrations of the molecule inside and outside of the cell. the direction of transport is determined simply by the relative concentrations of the molecule inside and outside of the cell. The net flow of molecules is always down their concentration gradient from a compartment with a high concentration to one with a lower concentration of the molecule. The net flow of molecules is always down their concentration gradient from a compartment with a high concentration to one with a lower concentration of the molecule. No membrane proteins are involved No membrane proteins are involved Simple diffusion

31 Model of an ion channel In the closed conformation, the flow of ions is blocked by a gate. In the closed conformation, the flow of ions is blocked by a gate. Opening of the gate allows ions to flow rapidly through the channel. Opening of the gate allows ions to flow rapidly through the channel. The channel contains a narrow pore that restricts passage to ions of the appropriate size and charge The channel contains a narrow pore that restricts passage to ions of the appropriate size and charge

32 Ligand-gated channels: open in response to the binding of neurotransmitters or other signaling molecules. Ligand-gated channels: open in response to the binding of neurotransmitters or other signaling molecules. Voltage-gated channels: open in response to changes in electric potential across the plasma membrane Voltage-gated channels: open in response to changes in electric potential across the plasma membrane

33 Simple diffusion - Ion channels The best-characterized channel proteins are the ion channels, which mediate the passage of ions across plasma membranes. The best-characterized channel proteins are the ion channels, which mediate the passage of ions across plasma membranes. Ion channels are present in the membranes of all cells. Ion channels are present in the membranes of all cells. They have been especially well studied in nerve and muscle, where their regulated opening and closing is responsible for the transmission of electric signals. They have been especially well studied in nerve and muscle, where their regulated opening and closing is responsible for the transmission of electric signals.

34 Simple diffusion - Ion channels Ion channels form open pores through the membrane, allowing the free diffusion of any molecule of the appropriate size and charge. Ion channels form open pores through the membrane, allowing the free diffusion of any molecule of the appropriate size and charge.

35 Facilitated Diffusion In facilitated diffusion molecules travel across the membrane in the direction determined by their concentration gradients. In facilitated diffusion molecules travel across the membrane in the direction determined by their concentration gradients. Charged molecules travel across the membrane in the direction determined by the electric potential across the membrane. Charged molecules travel across the membrane in the direction determined by the electric potential across the membrane. Facilitated diffusion allows polar and charged molecules, such as carbohydrates, amino acids, nucleosides, and ions, to cross the plasma membrane. Facilitated diffusion allows polar and charged molecules, such as carbohydrates, amino acids, nucleosides, and ions, to cross the plasma membrane. facilitated diffusion differs from passive diffusion in that the transported molecules do not dissolve in the phospholipid bilayer. facilitated diffusion differs from passive diffusion in that the transported molecules do not dissolve in the phospholipid bilayer. Instead, their passage is mediated by proteins that enable the Instead, their passage is mediated by proteins that enable the transported molecules to cross the membrane without directly transported molecules to cross the membrane without directly interacting with its hydrophobic interior interacting with its hydrophobic interior

36 Facilitated diffusion of glucose Facilitated diffusion of glucose The glucose transporter alternates between two conformations in which a glucose-binding site is alternately exposed on the outside and the inside of the cell. The glucose transporter alternates between two conformations in which a glucose-binding site is alternately exposed on the outside and the inside of the cell. In the first conformation shown (A), glucose binds to a site exposed on the outside of the plasma membrane. In the first conformation shown (A), glucose binds to a site exposed on the outside of the plasma membrane. The transporter then undergoes a conformational change such that the glucose-binding site faces the inside of the cell and glucose is released into the cytosol (B). The transporter then undergoes a conformational change such that the glucose-binding site faces the inside of the cell and glucose is released into the cytosol (B). The transporter then returns to its original conformation (C). The transporter then returns to its original conformation (C).

37 Carrier proteins Carrier proteins Needs energy Needs energy Active transport

38 Carrier proteins Carrier proteins bind specific molecules to be transported on one side of the membrane. Carrier proteins bind specific molecules to be transported on one side of the membrane. They undergo conformational changes that allow the molecule to pass through the membrane. They undergo conformational changes that allow the molecule to pass through the membrane. The molecules are then released on the other side. The molecules are then released on the other side. Carrier proteins are responsible for the facilitated diffusion of sugars, amino acids, and nucleosides across the plasma membranes of most cells Carrier proteins are responsible for the facilitated diffusion of sugars, amino acids, and nucleosides across the plasma membranes of most cells The glucose transporter provides a well-studied example of a carrier protein. The glucose transporter provides a well-studied example of a carrier protein.

39 Classes of carrier proteins Uniport (facilitated diffusion) carriers mediate transport of a single solute. An example is the GLUT1 glucose carrier. The ionophore valinomycin is also a uniport carrier.

40 A gradient of one substrate, usually an ion, may drive uphill (against the gradient) transport of a co-substrate. It is sometimes referred to as secondary active transport. Ex.:  glucose-Na + symport, in plasma membranes of some epithelial cells of some epithelial cells  bacterial lactose permease, a H + symport carrier.  bacterial lactose permease, a H + symport carrier. Symport (cotransport) carriers bind two dissimilar solutes (substrates) & transport them together across a membrane. Transport of the two solutes is obligatorily coupled.

41 A substrate binds & is transported. Then another substrate binds & is transported in the other direction. Only exchange is catalyzed, not net transport. The carrier protein cannot undergo the conformational transition in the absence of bound substrate. Antiport (exchange diffusion) carriers exchange one solute for another across a membrane. Usually antiporters exhibit "ping pong" kinetics.

42 Example of an antiport carrier: Adenine nucleotide translocase (ADP/ATP exchanger) catalyzes 1:1 exchange of ADP for ATP across the inner mitochondrial membrane.

43 Active transport enzymes couple net solute movement across a membrane to ATP hydrolysis. An active transport pump may be a uniporter or an antiporter.

44 Model of active transport: Energy derived from the hydrolysis of ATP is used to transport H+ against the electrochemical gradient (from low to high H+ concentration). Binding of H+ is accompanied by phosphorylation of the carrier protein, which induces a conformational change that drives H+ transport against the electrochemical gradient. Release of H+ and hydrolysis of the bound phosphate group then restore the carrier to its original conformation.

45 Active transport of glucose Active transport driven by the Na+ gradient is responsible for the uptake of glucose from the intestinal lumen. The transporter coordinately binds and transports one glucose and two Na+ into the cell. The transport of Na+ in the energetically favorable direction drives the uptake of glucose against its concentration gradient.

46 Na + -K + Pump

47 ENDOCYTOSIS : ENDOCYTOSIS : –Pinocytosis (Fluid & Adsorptive) –Phagocytosis EXOCYTOSIS: EXOCYTOSIS: ENDOCYTOSIS vs EXOCYTOSIS

48 Example of ENDOCYTOSIS : Phagocytosis of bacteria

49 Glut-2 G-6-P ATP ADP Glucose Voltage dependent Ca 2+ channel Ca 2+ K ATP Membrane depolarisation closed Example of Exocytosis TRAFFICKING Insulin granules SU Insulin exocytosis

50 Cytoplasm Thick clear, amorphous fluid that surrounds the nucleus Thick clear, amorphous fluid that surrounds the nucleus Contains all of the material needed by the cell to conduct life processes Contains all of the material needed by the cell to conduct life processes Fluid in cytoplasm is constantly moving and suspends other parts of the cell Fluid in cytoplasm is constantly moving and suspends other parts of the cell

51 The cytoplasm contains membranes and organelles suspended in a clear liquid called cytosol. contains membranes and organelles suspended in a clear liquid called cytosol. also contains abundant protein rods and tubules that form a supportive framework called the cytoskeleton. also contains abundant protein rods and tubules that form a supportive framework called the cytoskeleton. encircled by a thin membrane known as plasma membrane encircled by a thin membrane known as plasma membrane

52 Ribosomes Function: Synthesize proteins Golgi apparatus Function: Packages and modifies protein molecules for transport and secretion Function: Packages and modifies protein molecules for transport and secretion

53 Mitochondria Function: known as ‘power house’ of the cell. release energy from food molecule cell. release energy from food molecule and transform energy into usable and transform energy into usable form form

54 Lysosomes Function: contain enzymes capable of digesting worn cellular parts or substance that enter cells. Peroxisome Function: contain enzymes called peroxidases, important in the breakdown of many organic molecules.

55 Centrosome Function: helps distribute chromosomes to new cells during cell reproduction and initiates formation of cilia.

56 The nucleus Relatively large in size and spherical in shape. Relatively large in size and spherical in shape. Enclosed in a double layered nuclear envelop which consist of an inner and an outer lipid bilayer membrane. Enclosed in a double layered nuclear envelop which consist of an inner and an outer lipid bilayer membrane. These two membranes have a narrow space between them, but are joined at places that surround relatively large openings called nuclear pores. These two membranes have a narrow space between them, but are joined at places that surround relatively large openings called nuclear pores. The nuclear pores consist of more than 100 different types of proteins that allow substances to move between the nucleus and the cytoplasm, eg., messenger RNA. The nuclear pores consist of more than 100 different types of proteins that allow substances to move between the nucleus and the cytoplasm, eg., messenger RNA. The nucleus contains a fluid (nucleoplasm) in which other substances float: The nucleus contains a fluid (nucleoplasm) in which other substances float: 1. Nucleolus 1. Nucleolus 2. Chromatin 2. Chromatin

57 The Nucleus

58 Centrally located spherical cellular component which carries hereditary material ---- the DNA and controls all the vital activities of cytoplasm. Centrally located spherical cellular component which carries hereditary material ---- the DNA and controls all the vital activities of cytoplasm. Nuclear envelope and nucluoplasm Nuclear envelope and nucluoplasm Double-layered membrane --- Inner membrane and Outer membrane. Membrane is interrupted with pores. Nucleoplasm is rich in molecules for DNA replication, transcription and RNA production

59 The Nucleus Composition of the nucleus Composition of the nucleus –a. Nucleic acids –b. Protein –c. Enzymes –d. Surrounded by a double-layer membrane

60 CHROMOSOMES CHROMOSOMES consist of chromatins extensively folded into loops. Each chromosome contains a single DNA molecules with associated proteins. Chromosomes are only visible during mitosis and meiosis when their chromatin condenses.

61 CHROMOSOMES

62 NUCLEIC ACIDS THERE ARE TWO DIFFERENT TYPES OF NUCLEIC ACIDS, DNA AND RNA.

63 The nucleotides form a double helix. The function of DNA is serve as the basis of the genetic code. The function of DNA is serve as the basis of the genetic code. DNA contains the “instructions” for building the proteins needed by the cell. DNA contains the “instructions” for building the proteins needed by the cell. all DNA is restricted to the nucleus. all DNA is restricted to the nucleus. DNA (Deoxyribonucleic acid )

64 DNA DNA DNA is composed of a phosphate group a deoxyribose sugar and 4 nitrogen bases (A, C, G, T). In this formation: A bonds with T & C bonds with G only.

65 RNA It is a linear molecule similar to DNA except that it is single stranded and contains ribose instead of deoxyribose and Uracil in place of thymine. RNA is synthesized by the transcription of DNA catalyzed by RNA polymerase I, II and III.

66 RNA There are three types of RNA molecules that function in the cytoplasm of The cell: 1. Messenger RNA, 2. Transfer RNA, AND 3. Ribosomal RNA.

67 RNA - 3 types 1. mRNA carries the genetic code to the cytoplasm to direct the protein synthesis. 2. tRNA associated with specific amino acid that has been activated by enzyme. 3. rRNA associates with mRNA and tRNA during protein synthesis.

68 RNA THE FUNCTION OF RNA IS TO SYNTHESIZE PROTEINS USING THE GENETIC CODE OF DNA.

69 RIBOSOMES RIBOSOMES ARE THE SITE OF PROTEIN SYNTHESIS

70 RIBOSOMES CAN BE LOCATED FREE IN THE CYTOPLASM OR ASSOCIATED WITH THE ENDOPLASMIC RETICULUM

71 RIBOSOMES

72 Organelles - Ribosomes Structurally the ribosome consists of a small and larger subunit. Structurally the ribosome consists of a small and larger subunit.

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80 M/A of Aminoglycosides

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