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Lecture 4


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Lovaye Kajiura

1 ND TH WEEK 4: MONDAY, SEPTEMBER 23 TO FRIDAY, SEPTEMBER 27 , 2013 CHAPTER 4: CELL STRUCTURE & FUNCTION IClickr Review Questions: Characteristics of living organisms* Greatest threat to biodiversity in today’s world? Habitat loss What is the difference between a nonpolar covalent bond and a polar covalent bond? A polar covalent bond results when there is unequal sharing of electrons in a molecule, whereas electron are shared equally in a nonpolar covalent bond The reaction shown below is an example of : Know the Dehydration process diagram** The diagram shows: The four levels of protein structure The cell is the basic unit of structure and function in living organisms. What are the features that are shared by ALL cells? -cells are enclosed by a plasma membrane -cells use DNA as a hereditary blueprint -cells contain cytoplasm -cells obtain energy & nutrients from their environment -Cells need energy to drive metabolic functions, ultimate source of energy is the sun -Cell function limits cell size Fig. 4-1 Relative Sizes* Fig. 4-2 Plasma membrane* What are the TWO major types of cells? -Prokaryotic cells -Eukaryotic cells How do these cell types differ? -Prokaryotic cells – Genetic material is not enclosed in a membrane -Eukaryotic cells – Are structurally more complex cells; possess a membrane enclosed nucleus; Probably arose from prokaryotic cells Fig. E4-1 Microscopes yesterday & today * Fig. E4-2 A comparison of microscope images different micrographs* 2 EUKARYOTIC CELLS - Fungi, Protists, Plants, and Animals - are relatively larger in size compared to prokaryotic cells Fig. 4-3 A Generalized Animal Cell* KNOW STRUCTURE AND FUNCTION (DRAW DIAGRAM)! Fig. 4-4 A Generalized Plant Cell ^^^ Table 4-1 Functions and distribution of Cell Structures *** THE CYTOSKELETON Table 4-2 Major Components of the Eukaryotic Cytoskeleton *** know diagrams Fig. 4-5 The Cytoskeleton *** The cell’s cytoskeleton imparts structural support. The cytoskeleton is dynamic, since it alters to change the shape of cells, to move materials within the cell, to move the whole cell itself. Provides shape, support, & movement All organelles in the cell do not float about the cytoplasm, but instead are attached to a network of protein fibers called the cytoskeleton ------------------------------------------ Structure - are composed of actin filaments - strands of actin are intertwined 3 Functions - involved in maintenance of cell’s shape, cell motility (amoeboid movement), cell division (formation of cleavage furrow), cytoplasmic streaming, and organelle movement ---------------------------------------- Structure - most are made of keratin - fibrous proteins are wound to form thick cables -Microfilaments: Thin fibers -Intermediate Filaments: Medium-sized fibers -Microtubules: Thick fibers Functions - involved in maintenance of cell’s shape, anchors the nucleus and other organelles, Organelles -------------------------------- Structure - are composed of  tubulin monomer and  tubulin monomer - these two subunits form tubulin dimers Functions - involved in cell motility (flagella and cilia), movement of chromosomes during cell division (mitosis), maintenance of cell shape, and organelle movement Fig. 4-6 Cilia & flagella ** Fig. 4-7 How Cilia & flagella move ** 4 Fig. 4- 8 The Nucleus ** NUCLEUS - is surrounded by a nuclear envelope (a double membrane) - contains chromosomes (chromatin: DNA & histone proteins), which carry the cell’s genetic information - contains the nucleolus, which is the site of rRNA synthesis and ribosome assembly - nuclear pores are the opening in the nuclear envelope NUCLEAR ENVELOPE - controls passage of materials into and out of the nucleus - is a double membrane, which has pores through which water, ions, and small molecules can freely pass (DNA excluded) - has gatekeeper proteins that block the passage of certain large molecules - perforated with channels called the nuclear pores RIBOSOMES Fig. 4-10 A polyribosome - are made at the nucleolus - consist of small and large subunits - are involved in protein synthesis - some are present in the cytosol (fluid component of the cell’s cytoplasm) - eukaryotic ribosomes are composed of RNA and protein Why is the PLASMA MEMBRANE important? • It isolates the cell and may help it interact with its environment • the phospholipid bilayer contains globular proteins that regulate the transport of molecules into and out of the cell • Plant cells also have a rigid structure outside the plasma membrane called a cell wall which forms a protective coating 5 Fig. 4- • ENDOPLASMIC RETICULUM • forms channels within the cytoplasm • Rough ER is strudded with ribosomes (embedded) • Smooth ER 11 Endoplasmic reticulum may be rough or smooth ENDOPLASMIC RETICULUM -------------------------------------------------------- - consists of a network of membrane-bound tubules and sacs - ROUGH ER has ribosomes studded into the cytoplasmic surface of the membranes, where secreted and transmembrane proteins are manufactured - site where p
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