Chapter 4 Cell Structure and Function

What Are the Basic Attributes of Cells? All cells share common features DNA and RNA plasma membrane cytoplasm consists of all the fluid and structures that lie inside the plasma membrane but outside of the nucleus The fluid portion of the cytoplasm (cytosol) contains water, salts, and organic molecules Most of the cell’s metabolic activities occur in the cell cytoplasm

The Plasma Membrane Functions: glycoprotein carbo- hydrate extracellular fluid (outside) cytoplasm (inside) cholesterol membrane protein channel protein cytoskeleton A phospholipid bilayer helps to isolate the cell's contents Proteins help the cell communicate with its environment Functions: isolates the cell’s contents from the external environment regulates the exchange of essential substances allows communication between cells creates attachments within and between cells regulates biochemical reactions Phospholipid bilayer – allows the cell to maintain essential differences in concentrations of material. Proteins are responsible for exchanging and communicating, controlling reactions, and forming connections. 10,000 membranes stacked atop one another would scarcely equal the thickness of one page. Membranes vary from one tissue type to another, and their structures can also change dynamically in response to their surroundings. Fig. 4-2

Eukaryotic cells Plants, animals, protists, and fungi

A Generalized Animal Cell microfilaments nuclear envelope nuclear pore nucleus chromatin (DNA) cytosol nucleolus micro- (cytoskeleton) tubules flagellum basal body rough endoplasmic reticulum vesicle intermediate filaments (cytoskeleton) cytoplasm Golgi apparatus Organelles – membrane-enclosed structures, each specialized for a certain function. centriole ribosomes on rough ER lysosome smooth endoplasmic reticulum exocytosis of material from the cell mitochondrion plasma membrane Fig. 4-3 free ribosome

A Generalized Plant Cell nuclear envelope ribosomes nuclear pore intermediate filaments (cytoskeleton) nucleus chromatin nucleolus microtubules (cytoskeleton) cell walls of adjoining plant cells chloroplast cytoplasm rough endoplasmic reticulum lysosome smooth endoplasmic reticulum Golgi apparatus central vacuole vesicle mitochondrion cell wall plasma membrane plasmodesmata Fig. 4-4 cytosol plastid free ribosome

What Are the Major Features of Eukaryotic Cells? Cell walls outer surfaces of plants, fungi, and some protists Plant cell walls are composed of cellulose Fungal cell walls are made of chitin Cell walls are porous, allowing oxygen, carbon dioxide, and water carrying dissolved molecules to flow easily through them Plasmodesmata - openings that connect adjacent cells in plants The plasma membrane is located just beneath the cell wall 1. Nonliving, stiff coating secreted outside cell membrane. 2 & 3. some polysaccharides (including prokayrotes) Protists have cellulose, protein, or glassy silica. 4. Protective but also ….

What Are the Major Features of Eukaryotic Cells? microfilaments intermediate filaments microtubules microtubules (red) nucleus microfilaments (blue) (a) Cytoskeleton (b) Light micrograph showing the cytoskeleton Cytoskeleton provides shape, support, movement, cell division The cytoskeleton is composed of three types of protein fibers: microfilaments intermediate filaments microtubules Functions: shape and support (changes cell shape) cells without cell walls cell movement (cilia & flagella) organelle movement guide chromosomes and separate the dividing cell

Cytoskeleton Table 4-2

Cilia and Flagella Functions: 0.1 micrometer cilium plasma membrane basal body section of cilium central pair of microtubules protein “arms” Paramecium Functions: move the cell through fluid move fluid past the cell Both cilia and flagella are slender extensions of the plasma membrane supported by microtubules. Cilia means eyelash (shorter and numerous) Flagella means whip (longer, usually only 1 or 2) Both common in protists. Both contain a ring of 9 fused pairs of microtubules, with an unfused pair in the center.

How Cilia and Flagella Move cilia lining trachea propulsion of fluid (a) Cilium power stroke return stroke plasma membrane direction of locomotion propulsion of fluid flagellum of human sperm Requires energy to continuously undulate Cilia – energy similar to oars on a rowboat Flagella – energy compared to a propeller on a motorboat Paramecium use cilia to swim through water, others use flagella Cilia used in gills of oysters In mammals: Cilia – respiratory tract, female reproductive Flagella – any sperm surface of human egg cell (b) Flagellum continuous propulsion Fig. 4-7

The Nucleus Control center Nuclear envelope - consists of a double membrane perforated by nuclear pores Chromatin Nucleolus (b) Nucleus of a yeast cell (a) The nucleus nuclear envelope pores nucleolus ribosomes chromatin nucleus nuclear pores with nuclear pore complex Stores all information needed to construct the cell and direct the countless chemical reactions for life and reproduction. (make proteins) Largest organelle Isolated from the rest of the cell by a … nuclear pore complex are protein gatekeepers allowing RNA thru for protein synthesis 2. (colored substance) – chromosomes made of DNA when not dividing – extremely long, thin strands cannot see 3. (little nuclei) Site of ribosome assembly The nucleolus consists of ribosomal RNA, proteins, ribosomes in various stages of synthesis, and DNA

Ribosomes small particle composed of ribosomal RNA and proteins site of protein synthesis in the cytoplasm ribosome mRNA amino acid polyribosome growing protein Fig. 4-10

Endoplasmic Reticulum Vesicles are membranous sacs that transport substances The endoplasmic reticulum (ER) is a series of interconnected membranes that form a labyrinth of interconnected flattened sacs and channels within the cytoplasm All the proteins and phospholipids of cell membranes are synthesized in the ER Endomembrane system – loosely connected compartments. Segregate molecules from the surrounding cytosol and ensure orderly process of chemical reactions. Vesicles – temporary Reticulum means network

Endoplasmic Reticulum There are two forms of ER: Smooth endoplasmic reticulum has no ribosomes, detoxifies drugs, and synthesizes lipids like steroid hormones made from cholesterol Rough endoplasmic reticulum is studded with ribosomes and synthesizes proteins destined for other membranes or for secretion ribosomes smooth ER rough ER vesicles Smooth ER – scarce in most cells except liver, mammalian reproductive. detoxifies alcohol, metabolic wastes like ammonia

The Golgi Apparatus Functions: sorts, chemically alters, and packages important molecules It synthesizes some polysaccharides used in plant cell walls, such as cellulose and pectin It packages the finished molecules into vesicles that are then transported to other parts of the cell (lysosomes) or to the plasma membrane for export Vesicles from the ER merge with the Golgi apparatus Vesicles carrying modified protein leave the Golgi apparatus Golgi Named for the Italian cell biologist.

Lysosomes Serve as the cell’s digestive system Golgi apparatus digestive enzymes lysosome food vacuoles The Golgi apparatus modifies the enzymes as they pass through its compartments The enzymes are packaged into lysosomes, which bud from the (extracellular fluid) Digestive enzymes are synthesized on ribosomes and travel through the rough ER (cytoplasm) vesicles and travel to the Golgi apparatus A lysosome fuses with a food vacuole, and the enzymes digest the food 5 4 3 2 1 Serve as the cell’s digestive system A lysosome fuses with a food vacuole and digests food into basic nutrients Digest worn-out organelles Digest food from individual proteins to microorganisms like bacteria. Contain enzymes that can break down almost any type of biological molecule.

Vacuoles Serve many functions, including water regulation, support, and storage Most cells contain one or more sacs of cell membrane filled with fluid containing various molecules Many freshwater organisms possess contractile vacuoles composed of collecting ducts, a central reservoir, and a tube leading to a pore in the plasma membrane that carries excess water out of the organism Some vacuoles are temporary large vesicles (food vacuoles) Permanent vacuoles in some freshwater protists and in plant cells:

Contractile Vacuoles Fig. 4-15 contractile vacuole Water enters the collecting ducts and fills the central reservoir (a) Paramecium collecting ducts central reservoir pore Freshwater constantly leaks into contractile vacuoles through the cell membrane (osmosis). So much water would cause the organism to burst. Excrete the water by moving salt into collecting ducts then central reservoir. The reservoir contracts, expelling water through the pore Fig. 4-15 (b) Contractile vacuole

Vacuoles Central vacuoles Found in plants Functions: cytoplasm (a) Turgor pressure provides support central vacuole cell wall plasma membrane When water is plentiful, it fills the central vacuole, pushes the cytoplasm against the cell wall, and helps maintain the cell's shape When water is scarce, the central vacuole shrinks and the cell wall is unsupported Deprived of the support from water, the plant wilts Water pressure supports the leaves of this impatiens plant (b) Loss of turgor pressure causes the plant to wilt Vacuoles Central vacuoles Found in plants Functions: To maintain water balance To store hazardous wastes, nutrients, or pigments To provide turgor pressure on the cytoplasm to keep cells rigid which occupy three-quarters or more of the volume of many mature plant cells, are used in several ways: By regulating ion content of cytosol … As well as substances to deter animals from eating their leaves, nutrients (sugar and amino acids) not immediately needed, blue or purple pigments for the colors of flowers. Support. Substances attract water into it -> water pressure – turgor pressure provides support for the non-woody parts of the plant (when you forget to water your plants)

Mitochondria Extract energy from food molecules to make ATP “Powerhouse” of the cell Double membrane with cristae outer membrane inner matrix cristae 0.2 micrometer Found in large numbers of cells that are metabolically active (muscle) less in cartilage.

Chloroplast Site of photosynthesis Double membrane The thylakoid membranes contain the green pigment chlorophyll, which capture sunlight and make sugar from CO2 and water (photosynthesis) outer membrane inner stroma thylakoid channel interconnecting thylakoids granum (stack of thylakoids) 1 micrometer Plants and some protists. Stroma – fluid Thylakoid – a stack of hollow membranous sacs Chlorophyll captures the energy of sunlight and transfers it to other molecules in the thylakoid membranes. These molecules transfer the energy to ATP which diffuses into the stroma, where their energy is used to drive synthesis of sugar from CO2 and H2O.

Plastids Storage Only in plants and photosynthetic protists starch globules plastid 0.5 micrometer Storage Only in plants and photosynthetic protists Double membrane Storage containers for various molecules, such as pigments or starch Chloroplasts are highly specialized plastids. 3. Pigments that give ripe fruits their yellow, orange, or red colors. store photosynthetic products produced during the growing season for over winter Potatoes are composed almost entirely of cells stuffed with starch-filled plastids

Review Questions Describe the structures and features shared by all cells. Define organelle. Which organelles are found in plants not animals? Describe each major structure and know its function. DNA, RNA, plasma membrane, cytoplasm Membrane bound specialized structure in the cytoplasm Chloroplast, plastids, cell wall, vacuoles

prokaryotic cells

Prokaryotic Cells Are Simpler Than Eukaryotic Cells chromosome (nucleoid region) cell wall plasma membrane ribosomes capsule chromosome (nucleoid region) (d) Internal structure pili (c) Cocci ribosomes food granule prokaryotic flagellum (b) Spirilla capsule or slime layer cell wall plasma membrane cytoplasm plasmid (DNA) photosynthetic membranes (a) Generalized prokaryotic cell (bacillus) (e) Photosynthetic prokaryote Fig. 4-19

What Are the Major Features of Prokaryotic Cells? Most prokaryotic cells (bacteria) are less than 5 µm long, with a simple internal structure compared to eukaryotic cells They usually have a stiff cell wall Prokaryotic cells can take several shapes: Rod-shaped (bacilli) Spiral-shaped (spirilla) Spherical (cocci) Prokaryotic cells are small and possess specialized surface features Prokaryotic cells have fewer specialized structures within their cytoplasm (no organelles) Eukaryotic cells are 10-100um Single celled 2. Antibiotics interfere with cell wall synthesis, causing the bacteria to rupture.

What Are the Major Features of Prokaryotic Cells? Some bacteria and archaea are propelled by flagella Infectious bacteria may have polysaccharide adhesive capsules and slime layers on their surfaces Pili are protein projections in some bacteria that further enhance adhesion In the central region of the cell is an area called the nucleoid, which is separate from the cytoplasm Within the nucleoid is a single, circular chromosome of DNA Small rings of DNA (plasmids) are located in the cytoplasm None have cilia. Flagella is structured differently from eukaryotes. Capsules and slime layers are similar except that capsules are more organized structurally so more difficult to remove. Allows them to stick to surfaces, protect, and prevent drying out. Pili (hairs) from cell wall. attachment pili: short and abundant sex pili: few and long. Binds to a nearby bacterium of the same type and draws them together to exchange DNA. 4. Also has some RNA and protein The single DNA carries essential genetic info Plasmids carry genes that give the cell special properties (like inactivating antibodics)

What Are the Major Features of Prokaryotic Cells? No nuclear membrane or membrane-bound organelles Some have internal membranes used to capture light Extensive cytoskeleton The cytoplasm may contain food granules ribosomes 2. Some bacteria use membranes to organize enzymes for reactions. Lined up in order. Example … 3. Proteins differ but play similar roles 4. Food granules – store energy-rich molecules (glycogen) Ribosomes – protein synthesis but smaller and different RNA and proteins.

Review Questions Explain the major differences between prokaryotic and eukaryotic cells. Describe the structure and function of the major surface features of bacteria. Describe the internal features of bacteria.

A Protein Is Manufactured and Exported Vesicles merge with the plasma membrane and release antibodies into the extracellular fluid Vesicles fuse with the Golgi apparatus, and carbohydrates are added as the protein passes through the compartments The protein is packaged into vesicles and travels to the Golgi apparatus Antibody protein is synthesized on ribosomes and is transported into channels of the rough ER Completed glycoprotein antibodies are packaged into vesicles on the opposite side of the Golgi apparatus (extracellular fluid) (cytoplasm) vesicles Golgi apparatus forming vesicle 5 4 3 2 1 Fig. 4-13