Exercise 4 The Cell Anatomy and Division

Circle the correct underline term. During cytokinesis/interphase, the cell grows and performs its usual activities.

interphase

DNA replication occurs during ...

interphase

phases of mitosis

prophase, metaphase, anaphase, and telophase.

cytoplasm

surrounds the nucleus and other organelles - is surrounded by the plasma membrane

lysosomes

various-sized membranous sacs containing digestive enzymes including acid hydrolases; function to digest worn-out organelles and foreign substances that enter the cell. Have the capacity of total cell destruction if ruptured and are for this reason referred to as suicide sacs.

cell division

when the cell reproduces by itself by dividing

True or False. The end product of mitosis is four genetically identical daughter nuclei

False

True or False. All animal cell have a cell wall.

False.

Because these organelles are responsible for providing most of the ATP that the cell needs, they are often referred to as the powerhouses of the cell. They are the

mitochondria

animal cells have three major regions/parts that can be readily identified with a light microscope:

nucleus, plasma membrane, cytoplasm

Proteins are assembled on these organelles

ribosomes

golgi apparatus

stack of flattened sacs with bulbous ends and associated small vesicles; found close to the nucleus. Plays a role in packaging proteins or other substances for export from the cell or incorporation into the plasma membrane and in packaging lysosomal enzymes.

what is the name of the imaginary plane that the chromosomes align along?

The metaphase plate

during late prophase, what structure on the chromosome centromere do the growing spindle microtubules attach to? what structure is now present as fragments?

Kinetochores The nuclear envelope

briefly list four reasons why telophase is like the reverse of prophase

The events of telophase cause the chromosomes and cell structures to revert to their interphase appearance: the chromosomes uncoil, a nuclear envelope forms around each chromatin mass, nucleoli appear in the nucleus, and the spindle breaks down and disappears.

Late Prophase

The nuclear envelope break up allowing the spindle to interact with the chromosomes. Some of the growing spindle microtubules attach to kinetochores, special protein structures at each chromosome's centromere. Such microtubules are called kinetochore microtubules. The remaining spindle microtubules (not attached to any chromosomes are called polar microtubules. The microtubules slide past each other, forcing the poles apart. The kinetochore microtubules pull on each chromosome from both poles in a tug-of-war that ultimately draws the chromosomes to the center, or equator of the cell.

Define cell

The structural and functional unit of all living things.

meiosis

a specialized type of nuclear division that occurs only in the reproductive organs (testes or ovaries).

chromosomes

cells in the process of dividing to form daughter cells, the chromatin coils and condenses forming dense rodlike bodies

nucleoli

contained in the nucleus - one or more small spherical bodies - composed primarily of proteins and ribonucleic acid (RNA)

mitosis

division of the copied DNA of the mother cell to two daughter nuclei

cytokinesis

division of the cytoplasm, which begins when mitosis is nearly complete

telophase

final phase of mitosis - begin as soon as chromosomal movement stops. This final phase is like prophase in reverse. The identical sets of chromosomes at the opposite poles of the cell uncoil and resume their threadlike chromatin form. A new nuclear envelope forms around each chromatin mass, nucleoli reappear within the nuclei, and the spindle breaks down and disappears. Mitosis is now ended. The cll, for just a brief period, is binucleate (has two nuclei), and each new nucleus is identical to the original mother nucleus. cytokensis continues through and beyond this phase.

Prophase

first phase of mitosis - early prophase and late prophase

cytosol

fluid cytoplasmic material organelles are suspended in

cytokenisis

begins during late anaphase and continues through and beyond telophase. A contractile ring of actin microfilaments forms the cleavage furrow and pinches the cell apart.

When a cell is not dividing, the DNA is loosely spread throughout the nucleus in a threadlike form called

chromatin

plasma membrane

cytoplasm is enclosed by the plasm membrane

nuclear envelope

nucleus is bound by a double-layered porous membrane - similar in composition to other cellular membranes but it is distinguished but its large nuclear pores.

inclusions

the cell cytoplasm may or may not contain these. Examples of these are stored foods (glycogen granules and lipid droplets), pigment granules, crystals of various types, water vacuoles, and ingested foreign materials.

what does the twisted center of the cell represent

the centromere

How many stages of mitosis are there?

4

S

(interphase) DNA is replicated

organelles

"small organs" - metabolic machinery of the cell, and they are highly organized to carry out specific functions for the cell as a whole.

G2

(interphase) Final preparations for mitosis are completed and centrioles finish replicating

G1

(interphase) the centrioles begin replicating

interphase

the longer period during which the cell grows and carries out its usual activities

cell

the structural and functional unit of all living things - cells of human body are highly diverse, and their difference in size, shape and internal composition reflect their specific roles in the body.

cytoskeletal elements (microfilaments, intermediate filaments, and microtubules)

form an internal scaffolding called the cytoskeleton. Provide cellular support; function in intracellular transport. Microfilaments are formed largely of actin, a contractile protein, and thus are important in cell mobility, particularly in muscle cells. Intermediate filaments are stable elements composed of a variety of proteins and resist mechanical forces acting on cells. Microtubules form the internal structure of the centrioles and help determine cell shape.

mitochondria

generally rod-shaped bodies with a double-membrane wall; inner membrane is shaped into folds or cristae; contain enzymes that oxidize foodstuff to produce cellular energy (ATP); often referred to as "powerhouse of the cell".

chromatin

genetic material loosely dispersed throughout the nucleus n a threadlike form

Endoplasmic reticulum (ER)

membranous system of tubules that extends throughout the cytoplasm; two varieties; rough and smooth. Rough ER is studded with ribosomes; tubules of the rough ER provide an area for storage and transport of the proteins made on the ribosomes to other cell areas. Smooth ER, which has no function in protein synthesis, is a site of steroid and lipid synthesis, lipid metabolism, and drug detoxification

the structure that assembles during prophase is

mitotic spindle

nucleus

near the center of the cell; it contains genetic material (DNA) sections of which are called genes. It is often described as the control center of the cell. It is necessary for reproduction. A cell that has lost or ejected the nucleus is programmed to die.

centrioles

paired, cylindrical bodies that lie at right angles to each other, close to the nucleus. Internally, each centriole is composed of nine triplets of microtubules. As part of the centrosome, they direct the formation of the mitotic spindle during cell division; form the bases of cilia and flagella and in the role are called basal bodies.

mitosis

product = two daughter nuclei that are genetically identical to the mother nucleus

metaphase

second phase of mitosis - the two centrosomes are at opposite poles of the cell The chromosomes cluster at the midline of the cell, with their centromeres precisely aligned at the equator of the spindle. This imaginary plane midway between the poles is called the metaphase plate. Enzyme act to separate the chromatids from each other.

The plasma membrane not only provides a protective boundary for the cell but also determines which substances enter or exit the cell. We call this characteristic:

selective permeability

Plasma membrane

separates cell contents from the surrounding environment, providing a protective barrier. Its main structural building blocs are phospholipids (fats) and globular protein molecules.

peroxisomes

small lysosome-like membranous sacs containing oxidase enzymes and detoxify alcohol, free radicals, and other harmful chemicals. They are particularly abundant in liver and kidney cells.

nuclear pores

spanned by protein complexes that regulate what passes through, and they permit easy passes of protein and RNA molecules.

interphase

ther period when the cell carries out its normal metabolic activities and grows. Interphase is not part of mitosis. During this phase, the DNA-containing material is in the form of chromatin. The nuclear envelope and one or more nucleoli are intact and visible. The three periods during this phase are G1, S, and G2

selective permeability

valuable cell proteins and other substances are kept within the cell, and excreta or wastes pass to the exterior

early prophase

the chromatin condenses, formig barlike chromosomes each duplicated chromosome consists of two identical threads called sister chromatids held together at centromere. (Later when the chromatids separate, each will be a new chromosome.) As the chromosomes appear the nucleoli disappear and the two centrosomes separate from one another The centrosomes act as focal points for growth of a microtubule assembly called the mitotic spindle. As the microtubules lengthen, they propel the centrosomes toward opposite ends (poles) of the cell. Microtubule array called asters ("stars") extend from the centrosome matrix

anaphase

third phase of mitosis - the shortest phase of mitosis, begins abruptly as the centromeres of the chromosomes split simultaneously. Each chromatid now becomes a chromosome in its own right The kinetochore microtubules, moved along by motor proteins in the kinetochores gradually pull each chromosome toward the pole it faces. At the same time, the polar microtubules slide past each other, lengthen, and push the two poles of the cell apart. The moving chromosomes look V shaped. The centromeres lead the way, and the chromosomal "arms" dangle behind them. The fact that the chromosomes are short, compact bodies makes it easier for them to move and separate. Diffuse threads of chromatin would trail, tangle, and break, resulting in imprecise "parceling out" to the daughter cells. Late during this phase cytokensis begins.

microvilli

tiny fingerlike projections or folds - greatly increase surface area of the cell available for absorption or passage of materials and for the binding of signaling molecules.

ribosomes

tiny spherical bodies composed of RNA and protein; floating free or attached to a membranous structure (the rough ER) in the cytoplasm. Actual sites of protein synthesis