BIOL 425/001CH 3 NOTES Cells Very diverse Yet still similar Self contained Partially self-sufficient Bound by a membrane Inside membrane is cytoplasm, which contains various dissolved and suspended molecules as wellas structures called organelles Every cell contains DNA Prokaryotes “Before a nucleus” Archea and bacteria Lack a nucleus DNA is not surrounded by a membranous envelope DNA occurs as a large, circular molecule, with a variety of proteins loosely associated Known as bacterial choromose, localized in a region called the nucleoid Some bacteria do contain organelles, such as acidocalcisomes – thought to store energy and to help control acidity Eukaryote “With a true nucleus” The chromosomes are surrounded by a nuclear envelope, made of two membranes DNA is linear and tightly bound to special proteins known as histones Divided into organelles Compartmented by means of membranes that look similar among various organisms 3 layer appearance Termed “unit membrane” The Plant Cell: An Overview Cell Wall Protoplast Derived from the word “protoplasm”, meaning contents of the cell Protoplast – unit of protoplasm inside the cell Consists of cytoplasm and nucleus Cytoplasm- Membrane-bound entities Plastids Mitochondria- Systems of membranes Endoplasmic Reticulum Golgi apparatus- Nonmembranous entities Ribosomes Actin filaments Microtubules Nucleus Cytosol – rest of the cytoplasm – where everything is suspended Plasma Membrane- Mediates transport of substances into and out of the protoplast- Coordinates the synthesis and assembly of cell wall microfibrils- Detects and facilitates responses to hormonal and environmental signals involved in the control of cell growth and differentiation Vacuoles – bounded by a tonoplast (1 membrane) and is a liquid-filled cavity Cytoplasm is always in motion- Organelles are moved along in a current- This is known as cytoplasmic streaming or cyclosis- Contines as long as the cell is alive- Facilitates the transport of materials within the cell and between the cell and its environment Nucleus Controls the ongoing activities of the cell by determining which protein molecules are produced by the cell and when they are produced Stores genetic information, passing it on to daughter cells during division Nuclear genome – total genetic information stored in the nucleus Bounded by nuclear envelope Contains pores surrounded by an inner and outer membrane Pores have a complex structure that provide a direct passageway for the exchange of materials between the nucleus and the cytoplasm The other membrane of the nuclear envelope may be continuous with the endoplasmic reticulum Chromatin is found within the nucleoplasm (nuclear matrix) Made of DNA Forms chromosomes during division Nucleoli are also present High concentrations of RNA and proteins, along with large loops of DNA emanating from several chromosomes The loops of the DNA, known as nucleolar organizer regions, are the sites of formation of ribosomal RNA Ribosomes Formed in the cytosol Small particles consisting of protein and RNA RNA constitutes about 60% of the pass of a ribosome Site at which amino acids are linked together to form proteins Found free in the cytosol and attached to the endoplasmic reticulum Plastids and mitochondria contain smaller ribosomes Ribosomes aggregate into polysomes, or polyribosomes These are found near the ER and sometimes attached to the nuclear envelope Chloroplasts and other Plastids Concerned with processes of photosynthesis and storage Chloroplasts Site of photosynthesis Contain chlorophylls and carotenoid pigments Chlorophyll is responsible for the green color Chloroplasts are disk-shaped A single mesophyll cell may contain 40-50 chloroplasts Can reorient the chloroplasts under different light conditions (pp. 42) Thylakoids are found in the stroma Grana are stacks of disklike thylakoids (grana thylakoids) and thylakoids found in the stroma (stroma thylakoids) Chlorophyll and carotenoids are found throughout the thylakoid membranes Semiautonomous – like bacteria- Contain one or more nucleoid (DNA) that is not associated with histones- Small ribosomes Ultimate source of energy Involved in photosynthesis as well as the synthesis of amino acids and fatty acids Chromoplasts Contain pigments other than chlorophyll Synthesize and retain carotenoid pigments May develop for previously existing chloroplasts by a transformation in which the chlorophyll and internal membrane structure disappear This is what occurs when many fruits ripen Though to be an attractant to insects and other animals Leucoplasts Nonpigmented plastids Lack an elaborate system of inner membranes Amyloplasts – synthesize starch May also form oils and proteins Proplastids Precursor for other plastids Occur in meristematic cells of roots and shoots If development is arrested by the absence of light, it may form one or more prolamellar bodies, which are semicrystalline bodies composed of tubular membranes Plastids containing prolamellar bodies are etioplasts – form in leaf cells of plants grown in the dark – eventually develop chloroplasts and thylakoids from these when exposed to light Proplastids of seeds  etioplasts  chloroplasts Each plastid is bounded by an envelop consisting of two membranes Plastids may be differentiated into a system of membranes, or thylakoids and a matrix called the stroma Mitochondria Bounded by two membranes Cristae – invaginations Folds or tubules Greatly increase surface area available to proteins and the reactions associated with them Smaller than plastids Site of respiration Most plant cells contain hundreds of mitochondria Always in motion, turning, twisting, fusing, and dividing Contain components necessary for the synthesis of some, but not all, of their own proteins (Semiautonomous like plastids) Inner membrane Matrix containing proteins, RNA, DNA, small ribosomes, and solutes DNA occurs in nucleoids (like plastids) Mitochondria and Chloroplasts evolved from Bacteria Mitochondria and chloroplasts seem to have originated from a bacteria that was engulfed by a larger