CHAPTER 6 “THE CELL”
Dec 27, 2015
CHAPTER 6“THE CELL”
LIFE IS CELLULAR Cell Theory:1. All living things are made up of
cells2. Cells are the basic units of
structure & function in living things
3. New cells are produced from existing cells
ALL CELLS SHARE 2 CHARACTERISTICS1. A barrier called a cell membrane that surrounds the cell, and2. At some point in their lives they contain DNA. DNA is the molecule that carries biological information.
CELLS FALL INTO 2 BROAD GROUPS, BASED ON WHETHER THEY HAVE A NUCLEUS1. Prokaryotes: do not have nuclei. They have genetic material that is not contained in a nucleus. Bacteria are prokaryotes.
2. Eukaryotes are cells that have nuclei. Eukaryotes have a nucleus in which their genetic material is separated from the rest of the cell.• Plants, animals,
fungi, and protists are eukaryotes.
EUKARYOTIC CELL STRUCTURE• The eukaryotic
cell is divided into 2 main parts: the nucleus and the cytoplasm.
• The cytoplasm is the part of the cell outside the nucleus.
IN THE NUCLEUS
• The nucleus contains most of a cell’s DNA. The DNA contains the coded instructions for making proteins and other important molecules.
• The nucleus is surrounded by a double membrane called a nuclear envelope
• Inside the nucleus is chromatin. Chromatin is made up of DNA bound to proteins. When the cell divides, this chromatin condenses into chromosomes.
• Most nuclei also have a small, dense region known as the nucleolus where ribosomes are made.
IN THE CYTOPLASMEUKARYOTIC CELLS HAVE STRUCTURES CALLED ORGANELLES WITHIN THE CYTOPLASM.
Ribosomes are small particles of RNA and protein spread throughout the cytoplasm. Proteins are made on ribosomes.
The endoplasmic reticulum (ER) is an internal membrane system. The ER is where lipids are assembled, along with proteins and other materials that are exported from the cell.
2 types of ER: (1) Rough ER has ribosomes on its surface and is the site of protein synthesis; and, (2) Smooth ER which has no ribosomes and helps make lipids.
GOLGI Golgi Apparatus: job is to change,
sort, and package proteins and other materials from the ER for storage in the cell or secretion outside of the cell.
LYSOSOMES
Lysosomes are small organelles filled with enzymes.
They help break down lipids, carbohydrates, and proteins into smaller molecules that can be used by the rest of the cell.
Lysosomes can also play an important role in destroying harmful substances or bacteria that enter the cell.
VACUOLES Vacuoles are saclike structures
that are used to store materials.
MITOCHONDRIA Almost all
eukaryotic cells contain mitochondria.
Mitochondria convert the chemical energy stored in food into compounds that are more convenient for the cell to use.
CHLOROPLASTS Plants and some
other organisms contain chloroplasts.
Chloroplasts capture the energy in sunlight and convert it into chemical energy.
CYTOSKELETON
The structure that helps support the cell is called the cytoskeleton.
The cytoskeleton is a network of protein filaments that helps the cell maintain its shape.
It is also involved in movement.
ENDOMEMBRANE SYSTEM FOR THE AP STUDENT The ER is
continuous with the nuclear envelope
It encloses a network of interconnected tubules called cisternae.
SMOOTH ER Smooth ER serves diverse
functions in different cells Its enzymes are involved in
phospholipid and steroid synthesis, carbohydrate metabolism, and detoxification of drugs & poisons.
Alcohol and drugs increase a liver cell’s production of smooth ER, leading to an increased tolerance
Smooth ER also functions in storage and release of calcium ions during muscle contraction
ROUGH ER Rough ER manufactures
membranes for the cell. Enzymes built into the
membrane assemble phospholipids, and membrane proteins formed by bound ribosomes are inserted into the ER membrane
Transport vesicles transfer ER membrane to other parts of the endomembrane system.
GOLGI: SHIPPING AND RECEIVING CENTER The Golgi apparatus consists of a stack
of flattened sacs. Vesicles that bud from the er join to the
cis face of a Golgi stack, adding to their contents and membrane
Golgi products are processed and tagged from the cis to the trans face
Glycoproteins often have their attached carbohydrates modified
Golgi products are sorted into vesicles, which pinch off from the trans face
These vesicles may have surface molecules that help direct them to the plasma membrane or to other organelles.
LYSOSOMES: DIGESTIVE COMPARTMENTS Lysosomes are membrane-enclosed
sacs of hydrolytic enzymes used by animal cells to digest macromolecules
Lysosomes provide an acidic pH for these enzymes
In some protists, lysosomes fuse with food vacuoles to digest material ingested by phagocytosis.
Macrophages, a type of wbc, use lysosomes to destroy ingested bacteria
Lysosomes also recycle a cell’s own macromolecules by engulfing damaged organelles or small bits of cytosol, a process known as autophagy
THE ENDOMEMBRANE SYSTEM: A REVIEW As membranes move from the ER to the
Golgi and then to other organelles, their compositions, functions, and contents are modified.
MITOCHONDRIA & CHLOROPLASTS CHANGE ENERGY FROM ONE FORM TO ANOTHER Cellular respiration, the metabolic
processing of fuels to produce ATP, occurs within the mitochondria
Photosynthesis occurs in the chloroplasts of plants and algae, which produce organic compounds from CO2 & H2O by absorbing solar energy
Each contain a small amount of DNA that direct the synthesis of some of their proteins
MITOCHONDRIA: CHEMICAL ENERGY CONVERSION The folds of the inner
membrane, called cristae, create a large surface area and enclose the mitochondiral matrix.
Many respiratory enzymes, mitochondrial DNA, and ribosomes are housed in the matrix
CHLOROPLASTS: CAPTURE OF LIGHT ENERGY
Plastids are plant organelles that include amyloplasts, which store starch
Chromoplasts, which contain green pigments, and
Chloroplasts which contain the green pigment chlorophyll and function in photosynthesis
Chloroplasts are bounded by 2 membranes separated by a thin intermembrane space
Inside the inner membrane is a fluid called the stroma surrounding a membranous system of flattened sacs called thylakoids
Photosynthetic enzymes are embedded in the thylakoids, which may be stacked together to form structures called grana.
Chloroplast DNA, ribosomes, and many enzymes are contained in the stroma.
PEROXISOMES: OXIDATION Peroxisomes are oxidative organelles
filled with enzymes that function in a variety of metabolic pathways
They break down fatty acids for energy or detoxifying alcohol and other toxins
An enzyme that converts hydrogen peroxide (H2O2), a toxic by-product of these pathways, to water is also packaged within
CYTOSKELETON: SUPPORT, MOTILITY, AND REGULATION The cytoskeleton is a network of protein
fibers that give mechanical support, function in cell motility, & transmit mechanical signals from the cell’s surface to its interior.
The cytoskeleton interacts with special proteins called motor proteins to produce cellular movements
COMPONENTS OF THE CYTOSKELETON Three main types of fibers:
microtubules, microfilaments, and intermediate filaments
ALL eukaryotic cells have microtubules, which are hollow rods constructed of columns of globular proteins called tubulins
Microtubules change length through the addition or subtraction of tubulin dimers
In addition to providing a supportive framework, they also serve as tracks along which organelles move with the aid of motor molecules
In many animal cells, microtubules grow out from a region near the nucleus called a centrosome
A pair of centrioles, each composed of nine sets of triplet microtubules arranged in a ring, is associated with the centrosome and replicates before cell division
Yeast and plant cells lack centrosomes
Cilia and flagella are locomotor extensions of some eukaryotic cells
Cilia are numerous and short
Flagella occur one or two to a cell and are longer
Many protists use cilia or flagella to move through aqueous media
Cilia or flagella attached to stationary cells of a tissue move fluid past the cell
6.7 EXTRACELLULAR COMPONENTS AND CONNECTIONS BETWEEN CELLS HELP COORDINATE CELLULAR ACTIVITIES Plant cell walls are composed of microfibrils
of cellulose embedded in a matrix of polysaccharides and protein
The primary cell wall secreted by a young plant cell is relatively thin and flexible
Adjacent cells are glued together by the middle lamella, a thin layer of polysaccharides (pectin).
When they stop growing, some cells secrete a thicker and stronger secondary cell wall between the plasma membrane & primary cell wall.
the secondary wall, often deposited in several laminated layers, has a strong and durable matrix that affords the cell protection and support
Wood, for ex., consists mainly of secondary walls.
Plant cell walls are commonly perforated by channels between adjacent cells called plasmodesmata
EXTRACELLULAR MATRIX OF ANIMAL CELLS (ECM) Animal cells lack cell walls but do have an
elaborate ECM. The ecm is made of glycoproteins. The most
abundant glycoprotein is collagen, which forms strong fibers outside the cells
In fact, collagen accounts for about 40% of the total protein in the human body.
Cell surface receptor proteins called integrins that are built into the plasma membrane
Integrins are in a position to transmit signals between the ecm and cytoskeleton and thus to integrate changes occurring outside and inside the cell
INTERCELLULAR JUNCTIONS Plasmodesmata are channels in plant
cell walls through which the plasma membranes of bordering cells connect
Water, small solutes, and even some proteins and RNA molecules can move through these channels
THERE ARE 3 MAIN TYPES OF INTERCELLULAR JUNCTIONS BTW ANIMAL CELLS:1. Tight junctions: proteins hold adjacent cell membranes tightly together, creating an impermeable seal across a layer of epithelial cells.
2. Desmosomes (aka anchoring junctions): are reinforced by intermediate filaments and rivet cells into strong sheets
3. Gap junctions aka communicating junctions: are cytoplasmic connections that allow for the exchange of ions and small molecules between cells through protein-lined pores