Cell Structure - PDF

Cell structure Dr. Starling Emerald Dept. of Anatomy Cell structure Eukaryotic cells -possess a membranebound nucleus -Cytoplasm more complex than prokaryotic cells -compartmentalize many cellular functions within organelles and the endomembrane system -possess a cytoskeleton for support and to m...

Cell structure Dr. Starling Emerald Dept. of Anatomy Cell structure Eukaryotic cells -possess a membranebound nucleus -Cytoplasm more complex than prokaryotic cells -compartmentalize many cellular functions within organelles and the endomembrane system -possess a cytoskeleton for support and to maintain cellular structure -Plasma membrane 2 Eukaryotic Cells- Heredity Nucleus -stores the genetic material of the cell in the form of multiple, linear chromosomes -surrounded by a nuclear envelope composed of 2 phospholipid bilayers -in chromosomes – DNA is organized with proteins to form chromatin The nucleolus facilitates ribosome biogenesis, through the processing and assembly of rRNA into preribosomal particles General size of eukaryotes is 5-100 micrometers Nucleus: 5-10 micrometers (µm). How long is your DNA? If you stretched the DNA in one cell all the way out, it would be about 2m long Cellular Organization: Eukaryotic Chromosomes Eukaryotic chromosomes – -linear chromsomes -every species has a different number of chromosomes -composed of chromatin – a complex of DNA and proteins -heterochromatin – not expressed -euchromatin – expressed regions 5 Cellular Organization: Eukaryotic Chromosomes Chromosomes are very long and must be condensed to fit within the nucleus. -nucleosome – DNA wrapped around a core of 8 histone proteins -nucleosomes are spaced 200 nucleotides apart along the DNA -further coiling creates the 30-nm fiber or solenoid 6 Cellular Organization: Eukaryotic Chromosomes The solenoid is further compacted: -radial loops are held in place by scaffold proteins -scaffold of proteins is aided by a complex of proteins called condensin karyotype: the particular array of chromosomes of an organism 7 Cellular Organization: Eukaryotic Chromosomes Chromosomes must be replicated before cell division. -Replicated chromsomes are connected to each other at their kinetochores -cohesin – complex of proteins holding replicated chromosomes together -sister chromatids: 2 copies of the chromosome within the replicated chromosome 8 Endomembrane System Endomembrane system -a series of membranes throughout the cytoplasm -divides cell into compartments where different cellular functions occur 1. endoplasmic reticulum 2. Golgi apparatus 3. lysosomes 9 Endomembrane System Rough endoplasmic reticulum (RER) -membranes that create a network of channels throughout the cytoplasm -attachment of ribosomes to the membrane gives a rough appearance Function: synthesis of proteins to be secreted, sent to lysosomes or plasma membrane 10 Endomembrane System Smooth endoplasmic reticulum (SER) -relatively few ribosomes attached functions: -synthesis of membrane lipids -calcium storage -detoxification of foreign substances 11 Endomembrane System Golgi apparatus -flattened stacks of interconnected membranes -packaging and distribution of materials to different parts of the cell -synthesis of cell wall components 12 Endomembrane System Lysosomes -membrane bound vesicles containing digestive enzymes to break down macromolecules -destroy cells or foreign matter that the cell has engulfed by phagocytosis 13 Microbodies -membrane bound vesicles -contain enzymes -not part of the endomembrane system -glyoxysomes in plants contain enzymes for converting fats to carbohydrates -peroxisomes contain oxidative enzymes and catalase 14 Eukaryotic Cells Ribosomes -the site of protein synthesis in the cell -composed of ribosomal RNA and proteins -found within the cytosol of the cytoplasm and attached to internal membranes 15 Mitochondria Mitochondria -organelles present in all types of eukaryotic cells -contain oxidative metabolism enzymes for transferring the energy within macromolecules to ATP 16 Mitochondria -surrounded by 2 membranes -smooth outer membrane -folded inner membrane with layers called cristae -matrix is within the inner membrane -intermembrane space is located between the two membranes -contain their own DNA 17 Cytoskeleton -network of protein fibers found in all eukaryotic cells -supports the shape of the cell -keeps organelles in fixed locations -helps move materials within the cell 18 Cytoskeleton Cytoskeleton fibers include -actin filaments – responsible for cellular contractions, crawling -microtubules – provide organization to the cell and move materials within the cell -intermediate filaments – provide structural stability 19 Extracellular Structures Extracellular structures include: -cell walls of plants, fungi, some protists -extracellular matrix surrounding animal cells Extracellular matrix (ECM) -surrounds animal cells -composed of glycoproteins and fibrous proteins such as collagen -may be connected to the cytoplasm via integrin proteins present in the plasma membrane 20