A & P HW

Cytoplasm, plasma membrane and nucleus

A - panel A shows both a passive and active transport processes mediated by integral membrane proteins.

A carbohydrate molecular group. Panel D includes a membrane glycoprotein molecule. The carbohydrate components of this molecule are recognized by receptors present in the membranes of other cells.

It is a dynamic fluid structure that is in constant flux.

Junctions among epithelial cells lining the digestive tract.

Glucose Glucose, a small polar solute, uses a membrane transporter (a protein carrier) to cross the plasma membrane via facilitated diffusion. In simple diffusion, small nonpolar and lipid-soluble substances (including gases) diffuse directly through the lipid bilayer.

They are whiplike, motile cellular extensions that occur in large numbers on the exposed surfaces of certain cells. Cilia are whiplike, motile cellular extensions that occur, typically in large numbers, on the exposed surfaces of certain cells. Ciliary action moves substances in one direction across cell surfaces. Centrioles forming the bases of cilia and flagella are commonly referred to as basal bodies.

the absence of selective permeability allows water molecules that enter these damaged cells to also leave the cytoplasm. Skin is an organ made up of tissues, and tissues are made up of cells. Selective permeability requires an intact cell membrane.

exocytosis of secreted proteins. The event indicated by C includes the fusion of a secretory vesiclel with the plasma membrane and the subsequent release of the vesicle contents to the extracelluar space.

the use of a sodium concentration gradient to power the pumping of glucose into the cell. The sodium ion feel gradient is generated by the Na+-K+ pump at the left. Diffusion of sodium ions through the Na+-glucose symport (shown at the right) provides the energy necessary to actively transport glucose into the cell. Such a mechanism is used by intestinal cells (to absorb nutrients) and kidney cells (to recover glucose from urine prior to excretion).

to generate a sodium concentration gradient. The energy from ATP hydrolysis is used to transport sodium and potassium ions across the membrane and thereby establish concentration gradients for each of those ions.

Glucose is a hydrophilic molecule. Glucose and other monosaccharides are polar hydrophilic molecules that are not able to traverse the hydrophobic region of the phospholipid bilayer.

A Steroid molecules are nonpolar fat-soluble molecules, which would be expected to diffuse directly across the phospholipid bilayer. Such solutes do not require a membrane protein to facilitate transport.

none of the mechanisms require energy input All three mechanisms are forms of diffusion. Transport by diffusion of a molecule down its concentration gradient is a spontaneous process that requires no energy input.

an amino acid Mechanism B depicts the selective transport of a polar molecule such as an amino acid or sugar.

Selective permeability allows cells to exclude some substances and allow others to pass into or out of the cell. Selective permeability of the plasma membrane ensures that the continual traffic across the membrane does not include undesirable substances. It also ensures that desirable cell contents are retained within the cell.

Active transport is ATP dependent, whereas passive transport uses only the kinetic energy of the particles for movement across the plasma membrane. In active transport, the cell provides the metabolic energy (ATP) needed to move substances across the plasma membrane (against their concentration gradient). In passive transport, substances cross the plasma membrane (down their concentration gradient) using kinetic energy, without any energy input from the cell.

Osmosis A special name, osmosis, is given to the unassisted diffusion of a solvent, usually water, through a selectively permeable membrane.

hypertonic Hypertonic solutions have a higher concentration of nonpenetrating solutes than seen in the cell (for example, a strong saline solution). Cells immersed in hypertonic solutions lose water and shrink, or crenate.

In primary active transport, the transport protein gets phosphorylated; in secondary active transport, the transport protein is not phosphorylated. In primary active transport, energy comes directly from the hydrolysis of ATP and the subsequent phosphorylation of the primary active transporter. In secondary active transport, the solute (usually Na+) concentration gradient produced by primary active transport provides the (kinetic) energy to move other solutes, such as ions and glucose, against their concentration gradients. For example, glucose can be transported against its concentration gradient through a Na+-glucose symporter as Na+ moves down its concentration gradient (a gradient produced by the Na+-K+ pump).

During exocytosis, substances from inside the cell are moved outside. Vesicular transport processes that eject substances from the cell interior into the extracellular fluid are called exocytosis. Exocytosis is a form of active transport, thus it requires energy, usually in the form of ATP.

receptor-mediated endocytosis Receptor-mediated endocytosis is the main mechanism for the specific endocytosis and transcytosis of most macromolecules by body cells, and it is exquisitely selective. The mechanism also allows cells to concentrate material that is present only in very small amounts in the extracellular fluid.

phospholipids The plasma (cell) membrane is a phospholipid bilayer, composed of two parallel sheets of phospholipid molecules lying tail to tail, with their polar heads exposed to water on either side of the membrane. Each lollipop-shaped phospholipid molecule has a polar "head" that is charged and is hydrophilic (hydro = water, philic = loving), and an uncharged, nonpolar "tail" that is made of two fatty acid chains and is hydrophobic.

They are the main sites of ATP production. Mitochondria are threadlike or lozenge-shaped membranous organelles. In living cells they squirm, elongate, and change shape almost continuously. They are the power plants of a cell, providing most of its ATP supply.

ribosomes Proteins are synthesized at ribosomes. Free ribosomes float freely in the cytoplasm and produce soluble proteins that function in the cytosol, as well as those imported into mitochondria and some other organelles. Fixed ribosomes, which stud the rough endoplasmic reticulum, synthesize proteins destined either for incorporation into the cell membrane or lysosomes, or for export from the cell.

the activation of specific cytoplasmic enzymes Once activated by the binding of a specific chemical messenger, such as a hormone, the receptor initiates cellular responses by activating specific signal transduction pathways. These pathways include the activation of enzymes, such as kinases, that lead to specific cellular responses.

a mitochondrion

phospholipids Phospholipids are a major component of all cellular membranes, including the mitochondrial inner (A) and outer (B) membranes.

DNA molecule The mitochondria each have a small circular DNA chromosome that contains genes for several mitochondrial proteins. These proteins are translated within the mitochondria (on the ribosomes indicated by the small red dots). Most of the DNA in a cell is found in the nuclear chromosomes. Several muscular and nervous system diseases are associated with defects in mitochondrial DNA.

synthesis of secreted proteins Structure A is the rough endoplasmic reticulum (ER). The figure illustrates how proteins are synthesized on ribosomes bound to the rough ER, sorted in the Golgi, and delivered to the plasma membrane for secretion or packaged into lysosomes.

the Golgi apparatus Note how the location of the Golgi apparatus within the endomembrane system is consistent with its functions of sorting and modifying proteins being transported to various cellular locations.

hydrolytic enzymes Structure D is a lysosome, which stores enzymes that catalyze the hydrolysis (digestion) of organic cellular materials.

mitochondrion Mitochondria are the site of the majority of ATP production because of the specialized enzymes on their cristae.

cytoskeleton The cytoskeleton acts as the cell's "bones," "muscles," and "ligaments" by supporting cellular structures and providing the machinery to generate various cell movements.

is the site of ribosome assembly in a cell Nucleoli ("little nuclei") are the dark-staining spherical bodies found within the nucleus where ribosomal subunits are assembled. They are not membrane bounded. Typically, there are one or two nucleoli per nucleus, but there may be more. Nucleoli are usually large in growing cells that are making large amounts of tissue proteins.

DNA polymerase DNA polymerase is the enzyme that positions complementary nucleotides along the template strand and then covalently links them together into a new strand of DNA.

t-RNA t-RNA serves as an adapter molecule; it ferries amino acids to the ribosome and participates in translation (the process by which amino acids are assembled into proteins).

histone Histone proteins are the major structural protein associated with chromatin.

nucleosome The DNA helix wraps around a group of histone proteins to form a structural unit called a nucleosome.

breaking the bonds between complementary base pairs Structure A is the enzyme helicase, which untwists the DNA helix and breaks bonds between the complementary nucleotides of the two parental ("old") DNA strands.

joining the nucleotides that form the new DNA strand DNA polymerase catalyzes formation of bonds between sugar groups and phosphate groups that link the DNA nucleotides together.

one old parent strand and one new daughter strand. This mechanism is called semiconservative replication and is based on the ability of each strand of the DNA double helix to function as a template for the synthesis of the opposite strand.

B Molecule B is a complement of the DNA template (A) and contains ribonucleotides, as indicated by the presence of uracil (U). This is consistent with molecule B being an mRNA molecule.

transcription Transcription is the synthesis of RNA using DNA as a template.

a codon Note that each number corresponds to a group of three nucleotide bases within the mRNA molecule.

100 amino acids Each amino acid corresponds to a codon of 3 nucleotides. Therefore, a coding region of 300 nucleotides contains 100 codons and will produce a polypeptide of 100 amino acids in length.

ribosome The codons within the mRNA (B) are recognized by corresponding tRNA molecules within cytoplasmic ribosomes during protein translation.

Its DNA must be replicated exactly so that identical copies of the cell's genes can be passed on to each of its offspring. Before a body cell begins mitosis, it must replicate its DNA so that each daughter cell will have the same DNA as the parent cell.

transcription and translation Polypeptide synthesis involves two major steps: (1) transcription, in which DNA's information is encoded into mRNA, and (2) translation, in which the information carried by the mRNA is decoded and used to assemble polypeptides.

A molecule of RNA is formed based on the sequence of nucleotides in DNA. During transcription, RNA nucleotides line up with their complementary DNA partners, transcribing the information in DNA into RNA.

mRNA moves from the nucleus to the cytoplasm following RNA processing. mRNA undergoes RNA processing in the nucleus and then moves to the cytoplasm for translation.

ribosomes in the cell cytoplasm. Translation occurs at ribosomes in the cell cytoplasm.

DNA DNA contains the instructions for making proteins, but these instructions are transcribed to RNA before translation occurs.

mRNA attaches to the small subunit of a ribosome. mRNA attaches to the small subunit of a ribosome at the beginning of translation.

t-RNA t-RNA serves as an adapter molecule; it ferries amino acids to the ribosome and participates in translation (the process by which amino acids are assembled into proteins).

transcription and translation Polypeptide synthesis involves two major steps: (1) transcription, in which DNA's information is encoded into mRNA, and (2) translation, in which the information carried by the mRNA is decoded and used to assemble polypeptides.

stimulate blood vessels to develop within cartilage Cartilage is normally avascular, so nutrients required for healing must diffuse from distant blood vessels, which delays the healing process.

fibrous connective tissue is incapable of contracting Cardiac muscle contains sarcomeres, which allow for the tissue to contract when electrically stimulated. Fibrous connective tissue lacks these special contractile units.

Both are exocrine glands. Both glands secrete substances onto body surfaces or into body cavities.

salivary Merocrine glands, such as that shown in A, produce secretions such as saliva, sweat, digestive enzymes, and so on.

exocytosis Merocrine secretion involves the release of materials from intracellular secretory vesicles into the duct by exocytosis.

cell division Cells are regenerated by division in the basal layer and migrate toward the apical surface to replace cells lost by fragmentation. Cell division is indicated by the mitotic phase cells located in the deepest (basal) layer of the glandular epithelium.

epithelial tissue Epithelial tissue is a sheet of cells that covers a body surface or lines a body cavity (epithe = laid on, covering). In addition to coverings and linings, epithelial cells can also form glands, called glandular epithelium.

transitional epithelium Transitional epithelium forms the lining of hollow urinary organs, which stretch as they fill with urine. The ability of transitional cells to change their shape (undergo "transitions") allows a greater volume of urine to flow through the tube-like ureters and allows more urine to be stored in the urinary bladder.

endocrine glands Endocrine glands, which are ductless glands, secrete hormones into the interstitial fluid surrounding them. The hormones then diffuse toward and pass through a nearby capillary wall to enter the blood. Circulating throughout the body in the blood stream is how hormones eventually reach their target cells.

kidney: secretion kidney: filtration digestive tract: absorption skin: protection *skin: absorption The keratinized stratified squamous epithelium of skin is designed for protection, not absorption from the external environment.

microvilli Microvilli are small finger-like projections that greatly increase the surface area of epithelial cells (thus epithelial tissues), an important attribute of tissues that have a role in absorption and secretion.

Epithelial tissue is innervated. Epithelial tissue is an innervated, avascular tissue that exhibits polarity. Epithelial tissue is also highly regenerative.

Simple squamous epithelia are associated with filtration and exchange. Simple columnar epithelia are associated with absorption and secretion. *Simple cuboidal epithelia are found in areas that stretch. Stratified squamous epithelia are found in areas subjected to wear and tear. This is incorrect; transitional (not simple cuboidal) epithelia are found in areas that stretch, in particular the ureters and urinary bladder. Simple cuboidal epithelia are designed for absorption and secretion (not stretching).

in areas subjected to stretching Transitional epithelium is found in the urinary system. It lines the ureters, bladder and proximal part of the urethra-organs that are subjected to distention or stretching as urine passes through or fills them.

secrete substances onto body surfaces Exocrine glands use ducts to secrete substances into the external environment (onto the surfaces of the cutaneous and mucous membranes). Note: "exo" means outside. Endocrine glands are ductless; they secrete hormones into the extracellular fluid of our internal environment. Note: "endo" means inside.

Holocrine glands secrete their products by rupturing. Holocrine glands secrete their products by rupturing. Sebaceous (oil) glands are the only example of holocrine glands in the body.

unicellular exocrine glands Mucous cells are unicellular exocrine glands that secrete mucin, a protein that combines with water to form mucus.

Mucin Like mucous cells, goblet cells are unicellular exocrine glands that secrete mucin, a protein that combines with water to form mucus. In goblet cells, the cuplike accumulation of mucin distends the top of the cell, making these cells look like a glass with a stem, thus "goblet" cell. This distortion does not occur in mucous cells.

primarily consist of extracellular matrix All other primary tissues are composed mainly of cells, but connective tissues are largely nonliving extracellular matrix, which separates, often widely, the living cells of the tissue.

provide tensile strength Collagen fibers are extremely tough and provide high tensile strength (that is, the ability to resist being pulled apart) to the matrix. Stress tests show that collagen fibers are stronger than steel fibers of the same size!

2 Cell 2 is a fibroblast, which is the primary producer of the major ECM components in connective tissue proper.

5 Cell 5 is a mast cell, which produces and secretes inflammation-triggering chemicals such as histamine. Note the secretory granules within the pictured cell.

white blood cells Cell 3 (a lymphocyte) and cell 6 (a neutrophil) are two types of white blood cell.

Areolar connective tissue is avascular. Most connective tissues (except cartilage) contain blood vessels. A capillary is observed in the figure of areolar connective tissue.

keratin Keratin is a protein typically found in epithelial tissues, notably the cornified layers of the epidermis. Keratin would therefore not be found in significant quantities in the ECM of connective tissues.

the loose arrangement of its fibers The most obvious structural feature of this tissue is the loose arrangement of its fibers. The rest of the matrix, occupied by ground substance, appears to be empty space when viewed through the microscope. Note: the Latin term areola means "a small open space."

blood Blood, the fluid connective tissue (CT) within blood vessels, is the most atypical CT. It does not act as a binding or packing material; it does not provide structural support. It is classified as a CT only because it develops from mesenchyme and consists of cells (blood cells) surrounded by an extracellular fluid matrix (blood plasma).

bone: osteoblast Osteoblasts/cytes are the primary cell type for bone.

support protection *absorption insulation Absorption, the movement of substances into the body, is a role of epithelial tissue. Roles of connective tissue include: binding and support, protection, insulation, and transportation of substances, via blood, within the body.

*Dense connective tissue is often called fibrous connective tissue

Nervous tissue Nervous tissue regulates and controls body functions.

is under involuntary control Smooth and cardiac muscle are under involuntary control. Skeletal muscle is under voluntary control.

The cutaneous membrane is made of a simple columnar epithelium The cutaneous membrane, a "dry" membrane exposed to air, consists of a keratinized, stratified squamous epithelium called, the epidermis, and an underlying layer of connective tissue called, the dermis.

Epithelium is derived from all three primary germ layers: ectoderm, mesoderm, and endoderm. Mesoderm forms muscle and connective tissue. Ectoderm forms nervous tissue. Endoderm, mesoderm, and ectoderm all contribute to formation of epithelia.

cutaneous membrane The cutaneous membrane is your skin, an organ consisting of a keratinized stratified squamous epithelium (epidermis) firmly attached to a thick layer of connective tissue (dermis). Unlike other epithelial membranes, the cutaneous membrane is exposed to the air and is a dry membrane.

fibrosis Fibrosis involves proliferation of fibrous connective tissue, called scar tissue.

simple squamous epithelium Yes, this single layer of squamous cells is ideal for the diffusion of gases in the lungs.

simple cuboidal epithelium Yes, the simple cuboidal cells line the kidney tubules (nephrons) so that secretion and absorption can take place.

stratified squamous epithelium Yes, this epithelium protects underlying tissues from the wear and tear of constant swallowing in the esophagus.

soma Yes, the soma or cell body receives inputs (signals) from other cells and sends the information to the axon. But unlike a dendrite, it also is the main metabolic and nutritional center of the cell.

skeletal Yes, skeletal muscle cells are elongated and many can be quite long; therefore, they have multiple nuclei.

cardiac Yes, cardiac cells, like skeletal cells, have visible striations but are not under voluntary control.

False While pseudostratified epithelium has the illusion of being a multi-layered tissue, it is in fact made up of only one cell layer. The irregular heights of the cells in pseudostratified epithelia give the tissue a layered appearance. In reality, all of the cells in this tissue rest on the basement membrane (i.e., their basal surfaces are in contact with the basement membrane).

C Layer C consists primarily of dense, interwoven fibers of collagen designed to resist tearing from any direction.

dermis Although layers B and C can be distinguished based on their structural components, they form a continuous layer of the skin termed the dermis.

areolar connective tissue The loose connective tissue within the papillary layer of the dermis is rich in blood vessels and cells that function in the body's defenses.

subcutaneous The hypodermis ("under the skin") layer is also referred to as the subcutaneous region.

to supply cells to replace those lost from the epidermis The hypodermis does not perform this function. Cells to replace those lost in the epidermis are provided by the basal cells of the epidermis itself.

Structures A, B, C, and D are located in the dermis. Each of the labeled structures is located within the dermal layer of the skin.

keratinocytes Keratinocytes are the primary cells that form the stratified layers of the epidermis.

D Cells migrate upwards through the epidermis after being generated by mitosis in the stratum basale.

melanocyte Melanocytes within the stratum basale produce the pigment melanin, which is deposited within the deeper layers of the epidermis.

a dermal papilla Dermal papillae are projections of the dermis that form indentations in the overlying epidermis.

reticular layer There isn't a stratum reticulum. The epidermis of thick skin consists of 5 layers. From deep to superficial, these layers are stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum. (Study tip: Try the mnemonic BSGLC--Betty's Skin Glows Like Candles.) Thin skin lacks the stratum lucidum; thus, it consists of only the four major layers.

Tactile cells anchor the skin to the body. This is the incorrect statement. Tactile cells, in conjunction with their sensory nerve endings, function as touch receptors. The hypodermis, not tactile cells, anchors skin to the body.

False Keratin helps to provide a water barrier for the integument.

stratum basale Between 10 and 25% of the cells in the stratum basale are melanocytes that produce the melanin.

stratum basale The stratum basale is the deepest layer of the epidermis and consists of one layer of actively mitotic stem cells. The stem cells in this layer generate the cells that will migrate to the more superficial layers: spinosum, granulosum, and corneum.

pain receptors Pain receptors are found deeper in the papillary layer of the dermis.

melanin Melanin is the only one of the three pigments (melanin, carotene, and hemoglobin) that contribute to skin color that is actually produced in the skin itself.

the reticular layer The dermis has a collection of dense regular connective tissues with large amounts of collagen arranged in a regular pattern that creates cleavage lines.