AP Biology - Chapter 6

Organelles

The membrane-enclosed structures within eukaryotic cells.

Cell Fractionation

Cells are homogenized in a blender to break them up. The resulting mixture is centrifuged to separate the cellular components by centrifuging them at different speeds and times. This process results in pellets containing different cell components.

Lower Speeds = Larger Cellular Components

Higher Speeds = Smaller Cellular Components

Prokaryotic Cells are of what domains

Archaea and Bacteria

Eukaryotic Cells are of what domain

Eukarya

Cytosol

A semifluid, jellylike substance within the cell in which subcellular components are suspended.

Chromosomes

Carry genes in form of DNA

Eukaryotic Cell DNA Location

In an organelle called the nucleus, which is bounded by a double membrane.

Prokaryotic Cell DNA Location

The DNA is concentrated in a region that is not membrane-enclosed, called the nucleoid.

Cytoplasm

Interior of the cell

Cytoplasm in Eukaryotic Cells

In eukaryotic cells, this term refers only to the region between the nucleus and the plasma membrane.

Distinction between Prokaryotic and Eukaryotic Cells

Eukaryotic: Has nucleus and organelles; Much Larger and can be multi or unicellular.

Prokaryotic: Has nucleoid instead, and organelles are absent in almost all prokaryotic cells; Smaller and only unicellular.

Shared Features of Prokaryotic and Eukaryotic Cells

Plasma membrane: selective barrier of cell

Cytosol: semi-fluid, jellylike substance; subcellular components are suspended

Chromosomes: carry genes in the form of DNA

Ribosomes: tiny complexes that make proteins (not membrane-bound)

Cytoplasm: interior of the cell

Typical Size of Eukaryotic Cells

10-100 micrometers

Surface Area to Volume Ratio

A variable that decreases as cells grow, so that it sets a limit to the size of cells (Because area is squared and volume is cubed); Cells need a large surface area to volume ratio in order to be able to exchange materials with its surroundings.

Animal Cell Parts

Nucleus (nuclear envelope, nucleolus, chromatin), plasma membrane, ribosomes, golgi apparatus, lysosome, mitochondrion, peroxisome, microvilli, cytoskeleton (microfilaments, intermediate filaments, microtubules), centrosome, flagellum, endoplasmic reticulum (Rough ER & Smooth ER).

Nuclear Envelope

Double membrane enclosing the nucleus; perforated by pores, where at each lip of the pore, the inner and outer membranes of the nuclear envelope are continuous; continuous with ER

Nucleolus

Nonmembranous structure involved in production of ribosomes; a nucleus has one or more nucleoli

Chromatin

Material consisting of DNA and proteins that make up chromosomes; visible in a dividing cell as individual chromosomes

Plasma Membrane

Selective barrier of the cell which allows passage of enough oxygen, nutrients, and wastes to service the entire cell; Also called the cell membrane

Ribosomes

Tiny complexes that make proteins according to instructions from the genes; free in cytosol or bound to rough ER or nuclear envelope

Golgi Apparatus

Organelle active in synthesis, modification, sorting, and secretion of cell products.

Lysosome

Digestive organelle where macromolecules are hydrolyzed

Mitochondrion

Organelle where cellular respiration occurs and most ATP is generated

Peroxisome

Organelle with various specialized metabolic functions; produces hydrogen peroxide as a by-product and then converts it to water

Microvilli

Drastically increases surface area without an appreciable increase in volume through folded parts of the cell membrane; Typically in intestinal cells.

Cytoskeleton

Reinforces cell's shape; functions in cell movement; components are made of protein

Centrosome

Region where the cell's microtubules are initiated; contains a pair of centrioles

Flagellum

Motility structure present in some animal cells, composed of a cluster of microtubules within an extension of the plasma membrane

Endoplasmic Reticulum

Network of membranous sacs and tubes; active in membrane synthesis and other synthesis and metabolic processes; has rough (ribosome studded) and smooth regions.

Plant Cell Parts

Nucleus (nuclear envelope, nucleolus, chromatin), endoplasmic reticulum (smooth ER, rough ER), ribosomes, central vacuole, cytoskeleton (microfilaments, microtubules), chloroplast, plasmodesmata, cell wall, plasma membrane, peroxisome, mitochondrion, golgi apparatus.

Central vacuole

Prominent organelle in older plant cells; functions include storage, breakdown of waste products, and the hydrolysis of macromolecules; enlargement of the vacuole is a major mechanism of plant growth.

Chloroplast

Photosynthetic organelle; converts energy of sunlight to chemical energy stored in sugar molecules

Plasmodesmata

Cytoplasmic channels through cell walls that connect the cytoplasms of adjacent cells

Cell wall

Outer layer that maintains cell's shape and protects cell from mechanical damage; made of cellulose, other polysaccharides, and protein

Nucleus

Contains most of the genes in the eukaryotic cell (some genes are located in mitochondria and chloroplasts).

Nuclear Lamina

A netlike array of protein filaments (in animal cells, called intermediate filaments) that maintains the shape of the nucleus by mechanically supporting the nuclear envelope.

Pore Complex

An intricate protein structure that lines each pore and plays an important role in the cell by regulating the entry and exit of proteins and RNAs, as well as large complexes of macromolecules

Nuclear Matrix

A framework of protein fibers extending throughout the nuclear interior. The nuclear lamina and matrix may help organize the genetic material so it functions efficiently.

Chromosome Structure

Each chromosome contains one long DNA molecule associated with many proteins, including small basic proteins called histones.

Role of Proteins in Chromosomes

Some of these proteins help coil the DNA molecule of each chromosome, reducing its length and allowing it to fit into the nucleus.

Purpose of Nucleolus

Synthesizes rRNA from genes in the DNA. Also, proteins imported from the cytoplasm are assembled with rRNA into large and small subunits of ribosomes. These subunits then exit the nucleus throughout the nuclear pores to the cytoplasm and then combine into a ribosome.

How does the nucleus direct protein synthesis?

Synthesizes mRNA that carries information from the DNA. The mRNA is then transported to the cytoplasm via nuclear pores. Once an mRNA molecule reaches the cytoplasm, ribosomes translate the mRNA's genetic message in the primary structure of a specific polypeptide.

Parts of Ribosome

Made of ribosomal RNAs and proteins

Where do Ribosomes build proteins?

Free ribosomes are suspended in the cytosol, while bound ribosomes are attached to the outside of the endoplasmic reticulum or nuclear envelope. Free ribosomes make proteins that function in the cytosol and bound ribosomes make proteins that are destined for insertion into membranes, for packaging within certain organelles such as lysosomes or for export from the cell.

Endomembrane System

Includes the nuclear envelope, the endoplasmic reticulum, the golgi apparatus, lysosomes, various kinds of vesicles and vacuoles, and the plasma membrane.

Tasks of the Endomembrane System

Synthesis of proteins, transport of proteins into membranes and organelles or out of the cell, metabolism and movement of lipids, and detoxification of poisons.

Smooth Endoplasmic Reticulum

Function in diverse metabolic processes which vary with cell type. These processes include synthesis of lipids, including oils, steroids, and new membrane phospholipids. Other enzymes of the smooth ER help detoxify drugs and poisons, especially in liver cells. Smooth ER also stores calcium ions. In muscle cells smooth ER membrane pumps calcium ions from the cytosol into the ER lumen. When the muscle is stimulated, calcium ions rush back across the ER membrane into the cytosol and trigger contraction of the muscle cell.

Rough Endoplasmic Reticulum

Creates secretory proteins and is a membrane factory for the cell; it grows in place by adding membrane proteins and phospholipids to its own membrane and portions of it are transferred in the form of transport vesicles to other components of the endomembrane system.

Golgi Apparatus in the endomembrane system

Takes the vesicles from the ER and modifies the proteins form the ER and then sends it to other destinations. Also manufactures some macromolecules, such as polysaccharides.

Structure of Golgi

Consists of a group of associated, flattened membranous sacs called cisternae. Has a cis face, usually located near the ER and a trans face that gives rise to vesicles that pinch off and travel to other sites.

How does the Golgi perform it's functions?

Products of the ER are usually modified during their transit from the cis region to the trans region.

Lysosome enzymes work best in?

Acidic environments found in lysosomes

Construction of lysosomes

Hydrolytic enzymes and lysosomal membrane are made by rough ER and then transferred to the Golgi apparatus for further processing. Some lysosomes most likely arise from the trans face of the Golgi.

Function of Lysosomes

Carry out intracellular digestion in a variety of circumstances.

Vacuoles

Large vesicles derived from the ER and Golgi.

Food Vacuoles

Formed by phagocytosis

Contractile Vacuoles

Pump excess water out of the cell, thereby maintaining a suitable concentration of ions and molecules inside the cell.

Central Vacuole

Develops by the coalescence of smaller vacuoles. The solution inside the central vacuole is called cell sap, and is the plant's main repository of inorganic ions. Also allows the cell to become larger.

Endosymbiont theory

Mitochondria and chloroplast display similarities with bacteria. This theory states that an early ancestor of eukaryotic cells engulfed an oxygen-using non photosynthetic prokaryotic cell. Eventually this formed a relationship between the two.

Reasons for the Endosymbiont Theory

These two have double membranes. They also contain ribosomes, like prokaryotes. In addition, they contain circular DNA molecules which programs the synthesis of some organelle proteins as well. Furthermore, they are somewhat autonomous organelles that grow and reproduce within the cell.

Structure of Mitochondria

Smooth outer membrane and inner membrane folded into cristae. This inner membrane divides the mitochondrion into two internal compartments.

Internal compartments of Mitochondria

Intermembrane space: The narrow region between the inner and outer membranes

Mitochondrial matrix: Enclosed by the inner membrane and contains many different enzymes as well as the mitochondrial DNA and ribosomes.

Structure of Chloroplasts

Thylakoids: Flattened interconnected sacs

Granum: Each stake of thylakoids

Stroma: Fluid outside the thylakoids; contains the chloroplast DNA and ribosomes as well as many enzymes

Compartmentalization of Chloroplasts

Chloroplast is divided into three compartments: the intermembrane space, the stroma, and the thylakoid space. This allows for the chloroplast to convert light energy to chemical energy.

Plastids

A specialized family of closely related plant organelles; The chloroplast is one of them

Peroxisome function

Bounded by a single membrane, peroxisomes contain enzymes that remove hydrogen atoms from various substrates and transfer them to oxygen, producing hydrogen peroxide as a by-product. Some peroxisomes use oxygen to break fatty acids down to be used as fuel for mitochondria. Peroxisomes also detoxify alcohol and other harmful compounds by transferring hydrogen from the poisonous compounds to oxygen. The organelle also converts the H2O2 to water using an enzyme.

Cytoskeleton function

Supports the cell and also allows the cell to move. Also manipulates the plasma membrane, bending it inward to form food vacuoles or other phagocytic vesicles.

Cell mobility

Requires interaction of the cytoskeleton with motor proteins which use ATP.

Microtubules

Hollow tubes made up of tubulin

Microtubules function

Maintenance of cell shape, cell motility, chromosome movements in cell division, organelle movements

Intermediate Filaments

Fibrous proteins coiled into cables (keratins)

Intermediate filaments function

Maintenance of cell shape, anchorage of nucleus and certain other organelles, formation of nuclear lamina

Microfilaments

Two intertwined strands of actin

Microfilaments function

Maintenance of cell shape, changes in cell shape, muscle contraction, cytoplasmic streaming, cell motility, cell division

Centrioles

Within the centrosome is a pair of centrioles, each composed of nine sets of triplet microtubules arranged in a ring. They help organize microtubule assembly in animal cells.

Flagella and Cilia

Contain microtubules and allows for these structures to beat.

Flagella function

locomotion

Cilia function

move fluid, mucus, and materials over the cell surface; can also receive information for the cell.

Basal Body

The microtubule assembly of cilium or flagellum is anchored in the cell by a basal body, which is structurally very similar to a centriole.

Dyneins

Large motor proteins that bend the flagella and motile cilia. Walk along the microtubule of the adjacent doublet, using ATP for energy.

Cytoplasmic Streaming

Circular flow of cytoplasm which helps speed up movement of organelles and the distribution of materials within the cell.

Cell wall parts

Primary cell wall, and middle lamella which holds the primary walls of adjacent cells together. Other cells add a secondary cell wall between the plasma membrane and the primary wall.

Extracellular matrix

The ECM is made of glycoproteins and other carbohydrate-containing molecules secreted by the cells. Collagen, fibronectin, and proteoglycan molecules that consist of a small core protein with many carbohydrate chains covalently attached are part of the ECM.

Collagen

Fibers are embedded in a web of proteoglycan complexes.

Fibronectin

One ECM protein that attaches the ECM to integrins embedded in the plasma membrane. It also binds to associated proteins attached to microfilaments of the cytoskeleton.

Integrins

Transmit signals between the ECM and the cytoskeleton and thus to integrate changes occurring outside and inside the cell.

Tight Junctions

Membranes of neighboring cells are pressed together, preventing leakage of extracellular fluid

Desmosomes

Function like rivets, fastening cells together into strong sheets.

Gap Junctions

(communicating junctions) provide cytoplasmic channels between adjacent cells. Also create pores in which ions, sugars, amino acids, and other small molecules may pas through.