Introduction to Biochemistry PDF

INTRODUCTION TO BIOCHEMISTRY Dr.G.Krishnamoorthy,M.Sc.,M.Phil.,Ph.D Associate Professor Department of Medical Biochemistry Dembi Dollo University Cells make up all living things.  The cell is the structural & functional...

INTRODUCTION TO BIOCHEMISTRY Dr.G.Krishnamoorthy,M.Sc.,M.Phil.,Ph.D Associate Professor Department of Medical Biochemistry Dembi Dollo University Cells make up all living things.  The cell is the structural & functional unit of life It is regarded as the “basic unit of biological activity” CELLS Prokaryotes – lack well defined nucleus, has simple structure Eukaryotes – possess a well defined nucleus, has complex structure Structure of Eu-karyotic cell with cellular components or organelles Structure of Pro-karyotic cell with cellular components or organelles Difference between prokaryotic and Eukaryotic cells  It has well defined subcellular organelles, envelope by a plasma membrane The sub-cellular organelles are present in the cytoplasm. Eukaryotic Cytoplasm is the internal volume bounded by the plasma membrane cell The clear fluid portion of the cytoplasm in which th particles/organelles are suspended is called CYTOSO Cytosol also contains dissolved proteins, electrolyte & glucose  1. Nucleus The major 2. Mitochondria sub-cellular organelles 3. Endoplasmic reticulum are 4. Golgi apparatus 5. Lysosomes 6. Peroxisomes  It is the largest cell organelle All cells in the body contain nucleus, except mature RBCs in circulation. STRUCTURE 1. NUCLEUS Nucleus is surrounded by two membranes Outer membrane – continuous with membrane of endoplasmic reticulum Inner membrane – contain nuclear pores 2. Nucleus contains a dense body called NUCLEOLUS (involved in the synthesis of ribosomal RNA)  Nucleus contains the DNA, which is the hereditary material (condensed to chromosomes) DNA replication and RNA Functions synthesis are taking place inside of nucleus the nucleus. Marker for nucleus – DNA polymerase/RNA polymerase  STRUCTURE It consists of 2. MITOCHONDRIA a. Outer membrane – smooth, completely envelopes the organelle b. Inner membrane – is folded to form “cristae” c. Matrix – space within the inner membrane d. Intermembranal space-space between outer & inner membrane Functions of mitochondria 1. They are the powerhouse of the cell 2. They are involved in ATP production 3. Important metabolic pathways taking place in the mitochondria are TCA cycle, Urea cycle, Beta oxidation of fatty acids etc., 4. Mitochondria also contains specific DNA that encodes for mitochondrial proteins 5. Enzymes present in mitochondria-Inner membrane; matrix; intermembranal space  Clinical aspect LEBER’S HEREDITARY OPTIC NEUROPATHY – Caused due to mutation in the mitochondrial DNA that codes for a protein/enzyme called NADH- Coenzyme Q reductase Due to this, energy supply is affected & causes degeneration of optic nerves This may result in blindness  STRUCTURE & FUNCTION 1. The network of membrane enclosed spaces that extends throughout the cytoplasm forms the endoplasmic reticulum. 2. Types of endoplasmic reticulum (ER) a. Rough ER – Attached to ribosomes - Helps in protein synthesis b. Smooth ER – Not attached to ribosomes 3. ENDOPLASMIC - Involved in the synthesis RETICULUM of steroid hormones. - Also involved in Detoxification of drugs. 3. MARKER- a) Cholesterol desmolase (used in steroid hormone synthesis). b) NADPH cytochrome P450 reductase (used in detoxification of drugs) STRUCTURE OF ENDOPLASMIC RETICULUM  STRUCTURE & FUNCTION It is the network of flattened smooth membranes & vesicles It may be considered as the joining area of endoplasmic reticulum 4. GOLGI It is composed of Cis, medial and trans cisternae APPARATUS Functions – Protein sorting, packaging & secretion Marker-Galactosyl transferase/Mannosidase STRUCTURE OF GOLGI APPARATUS  STRUCTURE & FUNCTION 1. They are spherical vesicles enveloped by a single membrane formed from golgi apparatus 2. Lysosomes are called as “suicidal bags of the cell”, since they are actively involved in the digestion of cellular substances 5. LYSOSOMES 3. The lysosomal enzymes have an optimum pH around 5 4. Lysosomal enzymes are categorized as “Hydrolases” (hydrolytic enzymes) that act as markers for lysosomes Protein hydrolysing enzymes like – CATHEPSINS Lipid hydrolyzing enzymes like – PHOSPHOLIPASES Nucleic acid hydrolyzing enzymes - RIBONUCLEASES Clinical aspect GOUT – is a abnormal condition where uric acid crystals are digested by lysosomes – that leads to inflammation and arthritis in joints Lysosomal proteins – Cathepsins are involved in detection of tumor/cancer Inclusion cell disease (I-cell disease) – Lack of lysosomal enzymes – protein targeting defect – mannose 6 phosphate not added to proteins  They are also known as “microbodies” They are single membrane cellular organelles Peroxisomes contain enzymes like a. Catalase b. Peroxidase These enzymes are used for the removal of toxic peroxides from the 6. PEROXISOMES cell Peroxisomes also carry out beta oxidation of very long chain fatty acids CLINICAL ASPECT Zellweger syndrome: Genetic disease due to lack of peroxisomes in some tissues  The cell membrane is a complex barrier separating every cell from its external environment. This "Selectively Permeable" membrane regulates what passes into Plasma and out of the cell. membrane The cell membrane is a fluid mosaic of proteins floating in a phospholipid bilayer It functions like a gate, controlling which molecules can enter and leave the cell.  About 40% lipid and 50% protein 10% Carbohydrate , ~5 nm thick Similar in structure and composition to the prokaryotic inner membrane and highly selective pemeability barrier. Pumps and channels Plasma Enzymes Reception of extracellular membrane information Acts as a semi-permeable barrier Associated with several enzymes Contain receptors for hormones Contain recognition sites for antibodies Composition of different membrane content of various lipids in % Functions of Plasma Membrane It is selectively permeable membrane Its principal role is to regulate the flow of materials in and out of the cell; Carrier proteins in the membrane are involved in the transport of certain materials across the plasma membrane; In some cases it protects the inner cytoplasmic inclusions; it perceives the chemical stimulus.  Formation of Lipid Bilayer Membrane is often referred to as the phospholipid bilayer b/s made up of two layers of lipids Each contains a hydrophobic (water repelling) tail and a hydrophilic (water attracting) head hydrophobic tails oriented inside the bilayer while hydrophilic „polar‟ heads oriented exterior to wards water rich environments Not all lipids can form bilayers. A lipid bilayer can form only when the cross-sectional areas of the hydrophobic tail and hydrophilic polar head are about equal The hydrophobic effect and the solvent entropy provide the driving force for the formation of lipid bilayer  Fluid Mosaic Model of Cell Membranes The fluidity of the membrane are highly dependent upon the lipid composition of the membrane. Membranes are fluid(viscous like vegetable oil). The molecules of the cell membrane are always in motion, so the phospholipids are able to drift across the membrane, changing places with their neighbor. Proteins, both in and on the membrane, form a Mosaic. Because of this, scientists call the modern view of membrane structure the „Fluid Mosaic Model‟. Fluid Mosaic Model of Biomembrane The Components and Functions of the Plasma Membrane