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A TOUR OF THE CELL. Prokaryotic and eukaryotic cells differ in size and complexity All cells have several basic structures in common Within the membrane.

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Presentation on theme: "A TOUR OF THE CELL. Prokaryotic and eukaryotic cells differ in size and complexity All cells have several basic structures in common Within the membrane."— Presentation transcript:


2 Prokaryotic and eukaryotic cells differ in size and complexity All cells have several basic structures in common Within the membrane is a semi-fluid substance, cytoplasm, in which organelles are found All cells contain chromosomes, carrying genes in the form of DNA All cells have ribosomes At the boundary of every cell, the plasma membrane functions as a selective barrier that allows sufficient passage of oxygen, nutrients, and wastes

3 Major differences between prokaryotic and eukaryotic cells Chromosomes of a eukaryotic cell are found in a membrane-bound organelle called the nucleus The word prokaryotic is from the greek pro, before, and karyon, kernal, referring to the nucleus The eukaryotic cell (Greek eu, true, and karyon) has a true nucleus bound by a nuclear membrane

4 Within the cytoplasm of a eukaryotic cell are a variety of membrane bound organelles of specialized form and function These are absent in prokaryotic cells Eukaryotic cells are generally much bigger than prokaryotic cells Major differences between prokaryotic and eukaryotic cells





9 Venn Diagram Prokaryotic Both Eukaryotic

10 The Nucleus The nucleus contains most of the genes in the eukaryotic cell (some genes are located in the mitochondria and chloroplasts) The nuclear membrane is a double membrane, each a lipid bilayer with associated proteins Nuclear pores regulate the entry and exit of certain large macromolecules and particles


12 The Nucleus Within the nucleus is chromatin Chromatin consists of DNA and proteins The nucleolus functions in ribosome synthesis The nuclear envelope is perforated with pores

13 The Nucleus Within the nucleolus a special type of RNA called ribosomal RNA is synthesized and assembled with proteins imported from the cytoplasm The nucleus directs protein synthesis by synthesizing messenger RNA (mRNA) Once mRNA reaches the cytoplasm, it translates its genetic message into a polypeptide (protein)

14 Ribosomes Ribosomes build a cell’s proteins Ribosomes carry out protein synthesis Ribosomes are composed of two subunits Free ribosomes are suspended in the cytoplasm, while bound ribosomes are attached to the endoplasmic reticulum

15 Ribosomes

16 Endoplasmic Reticulum Smooth ER lacks ribosomes Rough ER appears rough because ribosomes stud the surface of its membrane

17 Functions of Smooth Endoplasmic Reticulum Enzymes of the smooth ER are important to the synthesis of lipids, including oils, phospholipids, and steriods Liver cells store carbohydrate in the form of glycogen, a polysaccharide The hydrolysis of glycogen leads to the release of glucose from the liver cells, which is important in the regulation of sugar concentration in the blood

18 Enzymes of the smooth ER help detoxify drugs and poisons, especially in enzymes Alcohol and many other drugs induce the proliferation of smooth ER This increases the tolerance to the drugs, meaning higher doses are required to achieve a particular effect Functions of Smooth Endoplasmic Reticulum

19 Many types of specialized cells secrete proteins produced by ribosomes attached to the rough ER Helps make and transport new proteins to the golgi apparatus or outside the cell For example, certain cells in the pancreas secrete the protein insulin, a hormone, into the bloodstream Functions of Rough Endoplasmic Reticulum

20 Golgi Apparatus The Golgi apparatus finishes, sorts, and ships cell products We can think of the Golgi as a center of manufacturing, warehousing, sorting, and shipping

21 Golgi Apparatus Products of the ER are modified and stored and then sent to other destinations The Golgi apparatus consists of flattened membranous sacs, cisternae Cisternae look like stacks of pita bread The two poles of the Golgi stack are reffered to as the cis face and the trans face

22 Golgi Apparatus The cis and trans faces act as the receiving and shipping departments of the Golgi apparatus The cis face is usually located near the ER Transport vesicles move material from the ER to the Golgi A vesicle that buds from the ER will add its membrane and the contents of its cavity to the cis face by fusing with a Golgi membrane The trans face gives rise to vesicles, which pinch off and travel to other sites

23 Lysosomes Lysosomes are digestive compartments A lysosome is a membrane-bounded sac of enzymes that the cell uses to digest macromolecules There are lysosomal enzymes that can hydrolyze proteins, polysaccharides, fats, and nucleic acids

24 Lysosomes Lysosomes digest (hydrolyze) materials taken into the cell and recycle materials White blood cells ingest bacteria and viruses and destroys them in the lysosomes Food vacuoles, formed by phagocytosis (engulfing smaller organisms or other food particles) fuse with lysosomes, whose enzymes digest the food

25 Vacuoles Membrane-bounded sacs Freshwater protists (eukaryotes) have contractile vacuoles that pump excess water out of the cell Mature plant cells contain a large central vacuole enclosed by a membrane called the tonoplast The plant’s central vacuole is usually the largest compartment of in a cell, compromising 80% or more of a mature cell Functions of the vacuole include storage, waste disposal, protection, and growth


27 Mitochondria Mitochondria are found in nearly all eukaryotic cells The mitochondrion is enclosed by two membranes, each a phospholipid bilayer with embedded proteins Proteins that function in respiration, including the enzyme that makes ATP, are built into the inner membrane

28 Mitochondria Mitochondria are the sites of cellular respiration, the catabolic process that generates ATP by extracting energy from sugar, fats, and other fuels with the help of oxygen Mitochondria contain ribosomes, and also contain a small amount of DNA Mitochondria DNA programs the synthesis of the proteins made on the organelle’s own ribosomes


30 Chloroplast The chloroplast is a specialized member of a family of closely related plant organelles called plastids A plastid’s function depends mostly upon which pigments are present Chloroplasts contain the green pigment chlorophyll Chloroplasts also contain enzymes and other molecules that function in the photosynthetic production of sugar

31 Chloroplast Like mitochondria, chloroplasts have two membranes Chloroplasts contain flattened sacs called thylakoids In some regions, thylakoids are stacked like pancakes; each stack is called a granum The fluid inside the chloroplast is the stroma, which contains the chloroplast DNA and ribosomes as well as many enzymes


33 Cell Wall Plants are encased by cell walls The cell wall is one of the features of plant cells that distinguishes them from animal cells The wall protects the plant cell, maintains its shape Prokaryotes, fungi, and some protists also have cell walls



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