hydrogen peroxide (a potentially dangerous free radical) – Other enzymes within the peroxisome then break down H 2 O 2 to oxygen and water • Peroxisomes • Peroxisomes protect the cell from potentially damaging effects of free radicals produced during catabolism • Their numbers are highest in metabolically active cells (the liver for example) • Mitochondria • Mitochondria are responsible for energy production – Aerobic metabolism (cellular respiration) • Number in cell varies with energy demand
• Mitochondria • Mitochondria have a double membrane – The outer membrane surrounds the organelle – The inner membrane contains numerous folds called cristae • What are the contents and structure of the nucleus? • The Nucleus • The nucleus is normally the largest and most conspicuous structure in the cell and is often the only visible structure under a light microscope • The nucleus is the “ control center ” for cellular operations • Nucleus • The nucleus stores all the information needed to direct synthesis of proteins needed for body • The nucleus determines the structure of the cell and what functions it can perform • True or False • All cells have one and only one nucleus? • Nucleus • Most cells have only one nucleus but exceptions do exist (some with more than one (skeletal muscle cells) some without (red blood cells) • The nucleus is surrounded by a double membrane nuclear envelope and, at several locations, the envelope is connected with endoplasmic reticulum • Nucleus • Chemical communication between cytosol and nucleus occurs through nuclear pores. – The pores are large enough to permit ions and small molecules to pass through but not proteins or DNA. • Pores contain regulatory proteins that govern the transport of proteins and RNA in and out of nucleus • Contents of the Nucleus • The Nucleoplasm is the fluid contents of the nucleus and contains the Nuclear matrix, a matrix of fine filaments providing structural support • The nucleoplasm also contains ions, enzymes, RNA and DNA nucleotides, small amounts of RNA, and DNA • Nuclear contents • Most nuclei contain nucleoli – Transient nuclear organelles that synthesize ribosomal RNA and ribosomal subunits • Are most prominent in cells that manufacture large amounts of proteins – Liver, nerve, muscle cells (need large amounts of ribosomes) • Nuclear contents • Nucleoli are compos ed of RNA, enzymes, and proteins called histones • Nucleoli form around portions of DNA that contain the instructions for producing ribosomal proteins and RNA when those instructions are being carried out • What does DNA do? • DNA • DNA stores the instructions for protein synthesis • DNA Organization • DNA strands are coiled around histones (proteins) forming a complex known as a nucleosome .
You've reached the end of your free preview.
Want to read all 11 pages?