6/28/2015 Cell is the base of life

6/28/2015 How can one define life? The simplest definition is that any living thing must have three general properties: metabolism growth reproduction

6/28/2015 Life's Hierarchy Life on Earth is incredibly extensive and, to make it easier to study, biologists have broken living systems up into generalized hierarchical levels: molecules; organells; cells; tissues; organs; organisms; populations

6/28/2015 Life's Hierarchy The focus of this course is on the fundamentals of life; that is, the properties that are held in common among all living things. We will concentrate almost exclusively on the molecular through the cellular level.

6/28/2015 The cell theory 1.Cells are the fundamental units of life, because a cell is the simplest unit capable of independent existence. 2.All living things are made of cells. This theory still holds true, with the minor caveat that viruses are only alive while infecting a cell. Mattias Schleiden and Theodor Schwann (1839) called cells “units of life” – cell theory.

6/28/2015 Cell elemental composition Cells are 90% water. The remaining molecules, the dry weight is approximately: 50% protein 15% carbohydrate 15% nucleic acid 10% lipid 10% miscellaneous

6/28/2015 Similarities between the pro- and eukaryotic types of cells 1.They both have DNA as their genetic material. 2.They are both membrane bound. 3.They both have ribosomes. 4.They have similar metabolism.

6/28/2015 Major differences 1.Eukaryotes have a nucleus and membrane-bound organelles, while prokaryotes do not. 2.Prokaryotic DNA floats freely around the cell; eukaryotic is held within its nucleus. 3.Eukaryotic/prokaryotic size is 10/1. 4.The DNA of eukaryotes is much more complex. 5.Prokaryotes have a cell wall composed of peptidoglycan, a polymer of amino acids and sugar. Some eukaryotic cells also have cell walls, but none made of peptidoglycan.

6/28/2015 Eukaryote cells (protozoa, fungi, higher animals and plants) Each eukaryote has a surrounding membrane - a thin layer of protein and fat that restricts the flow of substances in and out of the cell and encloses the cytoplasm, a jellylike material containing the nucleus and other structures (organelles) such as mitochondria. the nuclei of some cells contain a dense spherical structure called the nucleolus, which contains ribonucleic acid (RNA) for the synthesis of ribosomes.

6/28/2015 Animal cell structure

6/28/2015 Liver cell

6/28/2015 Liver cell nucleus and nucleolus

6/28/2015 Plant cell structure The plant cell is surrounded by: a plasma membrane and contains: a nucleus, ribosomes, ER, Golgi apparatus, mitochondria, peroxisomes, microfilaments and microtubules.

6/28/2015 Plant cell structure Plant cell also contains a family of membrane- enclosed organelles called plastids. The most important type of plastid is the chloroplast, which carries out photosynthesis, converting sunlight to chemical energy stored in sugar and other organic molecules.

6/28/2015 Plant cell structure The vacuole stores chemicals, breaks down macromolecules, and, by enlarging, plays a major role in plant growth. Another prominent organelle in many plant cells, especially older ones, is a large central vacuole.

6/28/2015 Plant cell structure The vacuole membrane is called the tonoplast. Outside a plant cell's plasma membrane (in fungi and some protists as well) is a thick cell wall.

6/28/2015 Plant cell structure It helps to maintain the cell's shape and protects the cell from mechanical damage. The cytosol of adjacent cells connects through trans-wall channels called plasmodesmata.

6/28/2015 Nucleus structure

6/28/2015 The nuclear envelope

6/28/2015 Nucleus with Nuclear Pores

6/28/2015 Ribosomes Ribosomes are the sites of protein synthesis. They are not membrane-bound and thus occur in both prokaryotes and eukaryotes. Eukaryotic ribosomes are slightly larger than prokaryotic ones.

6/28/2015 Ribosomes Structurally the ribosome consists of a small and larger subunit. Biochemically the ribosome consists of ribosomal RNA (rRNA) and some 50 structural proteins.ribosomal RNA Often ribosomes cluster on the endoplasmic reticulum, in which case they resemble a series of factories adjoining a railroad line.endoplasmic reticulum

6/28/2015 Structure of the ribosome Small subunit Large subunit

6/28/2015 Ribosomes Both free and bound ribosomes are abundant in this pancreas cell (TEM). The pancreas secretes hormones, including the protein insulin, into the bloodstream, and secretes digestive enzymes into the intestine.

6/28/2015 Ribosomes Bound ribosomes, those presently attached to the endoplasmic reticulum (ER), produce secretory proteins. Free ribosomes mainly make proteins that will remain dissolved in the cytosol. Bound and free ribosomes are identical and can alternate between these two roles.

6/28/2015 Ribosomes and Polyribosomes in liver cell

6/28/2015 The Endomembrane system A membranous system of interconnected tubules and cisternae Membranes of the endomembrane system vary in structure, composition, thickness and behavior The endomembrane system includes: Nuclear envelope Endoplasmatic reticulum Golgi apparatus Lysosomes Vacuoles Plasma membrane (related to endomembrane)

6/28/2015 The Endomembrane system A membranous system of interconnected tubules and flattened sacs called cisternae, the ER is also a continuous with the nuclear envelope. The membrane of the ER encloses a compartment called the cisternal space. Rough ER, which is studded on its outer surface with ribosomes, can be distinguished from smooth ER in the electron micrograph (TEM).

6/28/2015 The Endomembrane system Membranes in the endomembrane system are related either through: -direct physical continuity or -by the transfer of membrane segments as tiny vesicles. Endoplasmic reticulum is a mesh of interconnected membranes that serve a function involving protein synthesis and transport.

6/28/2015 Endoplasmatic reticulum (ER) ribosomes smooth ER cisternae cisternal space rough ER

6/28/2015 Endoplasmatic reticulum Rough endoplasmic reticulum (Rough ER) is so-named because of its rough appearance due to the numerous ribosomes that occur along the ER. Rough ER connects to the nuclear envelope through which the messenger RNA (mRNA) that is the blueprint for proteins travels to the ribosomes.

6/28/2015 Rough ER Newly synthesized proteins fold into its native conformation Most of the secretory proteins are glycoproteins (proteins covalently bound to carbohydrates Secretory proteins are kept separate from the other proteins to be remained in cytosol Secretory proteins leave the ER in transport vesicles

6/28/2015 Rough ER Another very important function of rough ER is the “production of the membrane” Proteins and phospholipids are added to the membrane They are either transported to rough ER or synthesized in rough ER (phospholipids)

6/28/2015 Smooth ER lacks the ribosomes characteristic of Rough ER and is thought to be involved in transport and metabolic processes including: synthesis of lipids (phospholipids and steroids), metabolism of carbohydrates, and detoxification of drugs and poisons

6/28/2015 Smooth ER Among the steroids produced by SER are: the sex hormones secreted by the adrenal glands; testes and ovaries are rich in smooth ER Role of smooth ER in carbohydrate metabolism is well presented by liver cells: liver cells store carbohydrate in the form of glycogen; phosphate molecule is removed from the glucose which can then live the cell

6/28/2015 Smooth ER Detoxification of drugs in liver cells mainly occur by adding hydroxyl groups to drugs. Hydroxylation makes drugs more soluble and more easier to flush from liver cells Unfortunately the exposure to barbiturates or alcohol forces the growth of smooth ER and subsequent increase tolerance to one of these agents

6/28/2015 Summary

6/28/2015 Summary

6/28/2015 Reading Campbell et al. Biology. Ch. 6 A tour of the cell,