Chapter 4 (cell Structure And Function)

Cell Structures

Lesson Objectives Students will be able to: ® Describe the key characteristics of the cell structures and their relative locations in the cell. ® Explain the function of the different cell structures. ® Explain the main differences in cell structures between Prokaryotes and Eukaryotes. 

The Cell Wall Gives the cell support ® Protects the cell ® Found in plants, fungi and bacteria. ®

Cell walls, cont… ® Cell

walls occur around the cell membrane. ® Thin,

flexible primary cell walls can still be divided ® A secondary cell wall, made when the cell deposits material inside the primary cell wall become lignified and are too rigid to divide.

The Cell Membrane Controls the exchange of materials such as nutrients and waste between cells and their environment. ® Found in all cells. ®

Cytoplasm ®

Clear, gelatinous fluid between the plasma membrane and the nucleus

Nuclear Envelope Separates the nucleus from the cytoplasm. ® Is a double- membrane, made of two lipid bylayers pressed together. ® The outer membrane merges with the membrane of the ER. ® The inner membrane has attachments for anchoring the DNA molecules. ®

The Nucleus

Contains the directions to make proteins. ® Controls activity of organelles. ® Contains chromatin, strands of DNA and associated proteins. ®

Ribosomes Molecular complexes that make proteins. ® Not bound by a membrane. ® To make proteins, the ribosomes leave the nucleus  cytoplasm, where mRNA code is converted into proteins ®

The Nucleolus ®

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Inside all nuclei is a nucleolus, an area dense with proteins making the subunits of ribosomes, which combine in the cytoplasm.

Organelles for Assembly and Transport of Proteins ® 1.

Endoplasmic Reticulum ® 2. Rough Endoplasmic Reticulum ® 3. Golgi Apparatus

Endoplasmic Reticulum (ER) Production and storage of lipids. ® Arranged in a series of highly folded membranes in the cytoplasm. ® Rough ER: Ribosomes are attached to endoplasmic reticulum. Site of Protein synthesis ®

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Golgi Apparatus Flattened stacks of tubular membranes ® Final modification of proteins. ® Sorts proteins into packages and packs them into membrane-bound organelles. ® Post office/UPS ®

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Read Fig 4.18, on pgs 62, 63 ®

Storage - Vacuoles Temporary storage of materials, particularly in plants and fungi ® A sac used to store food, enzymes, and other materials needed by a cell ® Store waste products ® Animals cells do not have a large, central vacuole ®

Lysosomes & Recycling Contain digestive enzymes to digest excess worn out organelles, food particles, engulfed viruses or bacteria. ® Membrane on the outside prevents digestion. ®

Energy Transformers ® Mitochondria ® Found

in all eukaryotic cells. ® ®

® Chloroplasts ® Found

in plants and some protists only.

Mitochondria Functions in energy production through metabolism ® Contains its own DNA (support for the endosymbiotic theory) ® Powerhouse/energy plant (make ATP from glucose) ®

Chloroplasts Surrounded by double membrane ® Responsible for photosynthesis, trapping light for synthesis of sugars ® Contains its own DNA ®

Support Structures ® Cytoskeleton ® Microtubules ® Microfilaments ® Centrioles

Cytoskeleton Forms framework for skeleton ® Microtubules – thin hollow cylinders made of protein called tubulin. ® Microfilaments – protein fiber that anchor & supports organelles. Made of actin ®

Centrioles ® ®

Assists in cell division. ® Occurs in pairs and made of microtubules. ®

Organelles for Locomotion Cilia – short, numerous projections that look like hairs (9+2 array) See pg 71 ® Flagella – one or more tails, a major means of locomotion ® Kinesin (pg 70) ®

Prokaryote VS Eukaryote

Prokaryote VS Eukaryote Feature

Prokaryote

Eukaryote

Size

Small about 0.5 micrometers

Up to 40 micrometers

Genetic material

Circular DNA (in cytoplasm)

DNA in form of linear chromosomes ( in nucleus)

Few present, none membrane bound

Many organelles: •Double membranes e.g.: nucleus, mitochondria & chloroplasts •Single membrane e.g.: GA, ER &

Organelles

lysosomes

Cell walls

Ribosome’s

Rigid formed from glycoproteins (mainly murein)

70s

•Fungi: rigid, formed from polysaccharide, chitin. •Plant: rigid, formed from polysaccharides. E.g.: cellulose. •Animals no cell wall

80s

Cell connections ® Animal

cells, which don’t have a cell wall, can secrete protein matrixes between cells to hold them together. ® Cell junctions are molecular structures that can send/receive messages or materials, and to recognize other cells. ® Adhering

junction (keep cells together, especially ones that move a lot). ® Gap junctions (can connect cellular cytoplasm between cells).