1 The nucleus Contains the cells genetic library
1. The nucleus: Contains the cell’s genetic library ﺍﻟﻤﺤﺘﻮﻯ ﺍﻟـﭽﻴﻨﻰ • The nucleus contains most of the genes in an eukaryotic cell. • The nucleus is separated from the cytoplasm by a double membrane ﻏﺸﺎﺀ ﻣﺰﺩﻭﺝ called nuclear membrane. • The nuclear membrane contains pores ﺛﻘﻮﺏ that allow large macromolecules and particles to pass through. • The nuclear membrane ﺍﻟﻐﻼﻑ ﺍﻟﻨﻮﻭﻯ is maintaining the shape of the nucleus 2
Fig. 7. 9, Page 116 3
• Within the nucleus, the DNA and associated proteins are organized into fibrous material, chromatin • In a normal cell they appear as diffuse mass. • However when the cell prepares to divide, the chromatin fibers coil up ﺗﻠﺘﻒ to be seen as separate structures, chromosomes • Each eukaryotic species has a characteristic number of chromosomes ﺭﻗﻢ ﻳﺯ ﻣﻦ ﺍﻟﻜﺮﻭﻣﻮﺳﻮﻣﺎﺕ. - A typical human cell has 46 chromosomes, but sex cells (eggs and sperm) have only 23 chromosomes. • Nucleolus is a dark region involved in production of ribosomes. • The nucleus directs protein synthesis by synthesizing messenger RNA (m. RNA). – The m. RNA travels to the cytoplasm and combines with ribosomes to translate its genetic message into the primary structure of a specific polypeptide. 4
2. Ribosomes : Build a cell’s proteins • Ribosomes contain r. RNA and protein. • A ribosome is composed of two subunits ﻭﺣﺪﺗﻴﻦ that combine ﺗﺘﺤﺪ to carry out protein synthesis. ﺣﺮﺓ ﻣﺮﺗﺒﻄﺔ Fig. 7. 10, Page 117 5
• In the nucleolus, ribosomal RNA (r. RNA) is synthesized and assembled with proteins from the cytoplasm to form ribosomal subunits. The subunits pass from the nuclear pores to the cytoplasm where they combine to form ribosomes. Cell types that synthesize large quantities of proteins (e. g. , pancreas) have large numbers of ribosomes. • • • 1. Ribosomes are 2 types: Free ribosomes are suspended ﻣﻌﻠﻖ in the cytosol and synthesize proteins that function within the cytosol. 2. Bound ribosomes are attached to ﻣﻠﺘﺼﻖ ﺑـ the outside of the endoplasmic reticulum. – These synthesize proteins that are either included into membranes or for export from the cell. 6
B- Eukaryotic Cell
3 - The Endomembrane System a) The endoplasmic reticulum ﺍﻟﺸﺒﻜﺔ ﺍﻹﻧﺪﻭﺑﻼﺯﻣﻴﺔ manufacturers membranes and performs many other biosynthetic functions b) The Golgi apparatus ﺟﻬﺎﺯ ﺟﻮﻟـﭽـﻰ finishes, sorts, and ships cell products c) The Lysosomes ﺍﻟﻴﺴﻮﺯﻭﻣﺎﺕ are digestive compartments d) The Vacuoles ﺍﻟﻔﺠﻮﺍﺕ have diverse functions in cell maintenance
A)- The endoplasmic reticulum manufacturers membranes and performs many other biosynthetic functions • The ER includes membranous tubules • There are two types of ER that differ in structure and function. 1. 2. Smooth ER looks smooth because it lacks ribosomes. Rough ER looks rough because ribosomes (bound ribosomes) are attached to the outside, including the outside of the nuclear envelope. Fig. 7. 11, Page 119 9
• The smooth ER: ﺍﻟﺸﺒﻜﺔ ﺍﻹﻧﺪﻭﺑﻼﺯﻣﻴﺔ ﺍﻟﻨﺎﻋﻤﺔ - It is rich in enzymes and plays a role in metabolic processes. - Its enzymes synthesize lipids ( ﺩﻫﻮﻥ oils, phospholipids, and steroids) including the sex hormones ﺍﻟﻬﺮﻣﻮﻧﺎﺕ ﺍﻟﺠﻨﺴﻴﺔ. - Extensive ﺗﻮﺟﺪ ﺑﻜﺜﺮﺓ in the liver, it helps detoxify ﺇﺑﻄﺎﻝ ﺍﻷﺜﺮ ﺍﻟﺴﺎﻡ drugs ﺍﻟﻤﺨﺪﺭﺍﺕ and poisons ﺍﻟﺴﻤﻮﻡ • The rough ER: ﺍﻟﺨﺸﻨﺔ ﺍﻟﺸﺒﻜﺔ ﺍﻹﻧﺪﻭﺑﻼﺯﻣﻴﺔ ER: - is especially abundant ﻣﺘﻮﻓﺮﺓ in those cells that secrete proteins as it contains ribosomes. - These secretory proteins are packaged in transport vesicles that carry them to their next stage.
B)- The Golgi apparatus: finishes, sorts ﺗﻫﺰ , and ships ﺗﻨﻘﻞ cell products • Many transport vesicles ﺃﻮﻋﻴﺔ ﻧﺎﻗﻠﺔ from the ER travel to the Golgi apparatus for modification ﺗﻄﻮﻳﺮ of their contents. • The Golgi is a center of manufacturing ﺗﺼﻨﻴﻊ , warehousing ﺗﻐﻠﻴﻒ , sorting ( ﺗﻫﻴﺰ packaging), and shipping ﻧﻘﻞ materals to outside the cell. • The Golgi apparatus is especially extensive in cells specialized for secretion ﺧﻼﻳﺎ ﺇﻓﺮﺍﺯﻳﺔ. • The Golgi also manufactures pectin and polysaccharides. 11
C)- Lysosomes ﺍﻷﺠﺴﺎﻡ ﺍﻟﺣﻠﻠﺔ are digestive components • The lysosome is a membrane-bounded sac of enzymes that digests macromolecules. Fig. 7. 13 a, Page 13121
Lysozomal enzymes Lysosomal enzymes work best at p. H = 5 (acidic). The lysosomal enzymes are synthesized by rough ER and then transferred to ﺗﻨﻘﻞ ﺇﻟﻰ the Golgi then to lysosomes. Function of Lysozomal enzymes 1) They hydrolyse ﻳﺤﻠﻞ proteins, fats, polysaccharides, and nucleic acids. 2) Can destroy the cell by autodigestion (autophagy) ﺍﻟﻬﻀﻢ ﺍﻟﺬﺍﺗﻰ. 3) Can fuse with food vacuoles ﺍﻟﻔﺤﺠﻮﺓ ﺍﻟﻐﺬﺍﺋﻴﺔ to digest food, (when a food item is brought into the cell by phagocytosis). 4) Can also fuse with another organelle or part of the cytosol. This process of autophagy called recycling which renews the cell
Fig. 7. 14, Page 122 15
D)- Vacuoles ﺍﻟﻔﺠﻮﺍﺕ : Have diverse functions ﻭﻇﺎﺋﻒ ﻣﺘﻨﻮﻋﺔ in cell maintenance ﻟﻠﺤﻔﺎﻅ ﻋﻠﻰ ﺍﻟﺨﻠﻴﺔ • Vesicles ﺃﻮﻋـﻴﺔ and vacuoles ﻓﺠﻮﺍﺕ are membranebound sacs ﺃﻜﻴﺎﺱ with varied functions. 1. Food vacuoles, vacuoles from phagocytosis, fuse with lysosomes. 2. Contractile vacuoles, vacuoles found in freshwater protists, pump excess water out of the cell. 3. Central vacuoles are found in many mature plant cells. 16
• The membrane surrounding the central vacuole, the tonoplast, is selective ﺇﺧﺘﻴﺎﺭﻯ ﺍﻟﻨﻔﺎﺯﻳﺔ in its transport of materials into the central vacuole. • The functions of the central vacuole include storing proteins or inorganic ions, depositing metabolic byproducts ﺗﺮﺳﻴﺐ ﻧﻮﺍﺗﺞ ﺍﻷﻴﺾ ﺍﻟﺜﺎﻧﻮﻳﺔ , storing pigments ﺗﺨﺰﻳﻦ ﺍﻷﺼﺒﺎﻍ. • It also increases internal surface of the cell. 18
Other Membranous Organelles A)- Peroxisomes contain enzymes that transfer hydrogen from various substrates to oxygen Functions of peroxisomes 1 - Hydrogen peroxide (H 2 O 2) is a poison, but the peroxisome has enzyme that converts H 2 O 2 to water. 2 - Some peroxisomes break fatty acids down to smaller molecules that are transported to mitochondria for fuel ﻹﻧﺘﺎﺝ ﺍﻟﻄﺎﻗﺔ. ﻹﻧﺘﺎﺝ 3 - They detoxify ﻳﺒﻄﻞ ﺍﻟﻤﻔﻌﻮﻝ ﺍﻟ ﻣﻰ alcohol and other harmful compounds. Thus, it exists extensively in the liver cells
B)- Mitochondria: Mitochondria and chloroplasts are the main energy transformers of cells • Mitochondria and chloroplasts are the organelles that convert energy to forms that cells can use for work. • Mitochondria are the sites of cellular respiration, generating ﺗﻧﺝ ATP from the catabolism ﻫﺪﻡ of sugars, fats, and other fuels ﻣﺼﺎﺩﺭ ﻃﺎﻗﺔ in the presence of oxygen. • Chloroplasts, Chloroplasts found in plants and eukaryotic algae ﻃﺤﺎﻟﺐ , are the site of photosynthesis. - They convert solar energy ﺗﺤﻮﻝ ﺍﻟﻄﺎﻗﺔ ﺍﻟﺸﻤﺴﻴﺔ to chemical energy and synthesize new organic compounds from CO 2 and H 2 O. • Mitochondria and chloroplasts are not part of the endomembrane system. • Almost all eukaryotic cells have mitochondria. • Mitochondria and chloroplasts are mobile and move around the cell along tracks in the cytoskeleton. 20
• Mitochondria have a smooth outer membrane and a highly folded inner membrane forming cristae ﻧﺘﻮﺀﺍﺕ. • The inner membrane encloses the mitochondrial matrix, matrix a fluid-filled space with DNA, ribosomes, and enzymes. Fig. 7. 17, Page 124
• The chloroplast produces sugar via photosynthesis. – Chloroplasts gain their color from high levels of the green pigment chlorophyll • Chloroplasts measure about 2 microns x 5 microns and are found in leaves and other green structures of plants and in eukaryotic algae. 22 Fig. 7. 18, Page 125
• The processes in the chloroplast are separated from the cytosol by two membranes. • Inside the innermost membrane is a fluid-filled space, the stroma, in which float membranous sacs, the thylakoids. – The stroma contains DNA, ribosomes, and enzymes for part of photosynthesis. – The thylakoids, flattened sacs, are stacked into grana and are critical for converting light to chemical energy. 23
Fig. 7. 18 24 Copyright © 2002 Pearson Education, Inc. , publishing as Benjamin Cummings
- Slides: 24