Animal Cell Structure

7/28/2019 Animal Cell Structure

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Animal Cell Structure

Cells have many organelles that perform various functions important to the cell's

survival.

The cell membrane is located around the outside of the cell. It is a proteinlipid bilayer. The hydrophilic heads of the lipids point outwards while the

hydrophobic tails occupy the space between the two lipid layers. Several types

ofproteins are imbedded in the membrane: channel, transport, recognition,

receptor, and electron transfer. Channel proteins provide passageways through

the membrane for small substances to diffuse through. Transport proteins are

involved in theactive transport of substances across the membrane.

Recognition proteins recognize other cells. Receptor proteins are receptor sites

for hormones and other chemicals. Electron transfer proteins are involved in

the transfer of electrons in processes likephotosynthesisandcellular

respiration. Because the proteins constantly shift throughout the cell membrane,

it is referred to as a fluid mosaic model. The functions of the cell membrane

include: holding cellular material, regulating the movement of materials across

the membrane, providing a surface for many chemical reactions, and identifying

the cell to the body's immune system.

Cell junctions connect one cell to another. Gap junctions are found in animalsand are very, very small channels that allow various ions and other small

substances to pass from one cell to another. Tight junctions are seals around

cells to prevent leakage. They are important for containing liquids like stomachacids. Desmosomes are spot welds that hold cells together.

The nucleus controls the cell's activities and contains all the genetic material(46chromosomes in humans).

The nucleolus is involved in the synthesis ofribosomal RNA. It is a dark bodyinside the nucleus.

The nuclear membrane keeps DNA inside the nucleus but allows mRNA andproteins through. It is a double membrane with large pores.

Ribosomes assemble proteins from RNA codes. They are found free-floating inthe cytoplasm throughout the cell or attached to the endoplasmic reticulum.

The smooth endoplasmic reticulum is a series of long canals runningthroughout the cell. It detoxifies the cell and converts foodstuffs.

The rough endoplasmic reticulum is a series of long canals running throughoutthe cell with ribosomes attached. It transports proteins to the golgi bodies for
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packaging.

Golgi bodies (also apparatus or complex) store and package cellular secretionsfor export out of the cell (usually through the use of vacuoles). Salivary, oil,

and digestive glands have very active golgi bodies.

Lysosomes digest and remove worn out cell organelles. In essence, they arevacuoles filled with digestiveenzymes.

Mitochondria produce most of the cell's energy. They are composed of twomembranes (an outer and a folded inner membrane) and are common in

muscle cells.

Centrioles anchor spindle fibers duringcell division. They are composed ofmicrotubules and are only found in animal cells.

The cell's cytoskeleton provides the cell with shape and support. It is involvedin cell movement (cytoplasmic streaming, muscle contraction, ameboid

movement, and cell division). The cytoskeleton is composed ofactin filaments,

intermediate filaments, and microtubules.

Vacuoles are "bubbles" of material in the cell. Usually vacuoles hold water. Theand solid material as well.

Some cells have microvilli to aid in movement or absorption.Cell membrane

The Cell membrane is abiological membrane that separates the interior of all cells

from theoutside environment.[1]The cell membrane isselectively permeable to ions

and organic molecules and controls the movement of substances in and out of cells.[2]

The basic function of the cell membrane is to protect the cell from its surroundings. It

consists of thelipid bilayer with embedded proteins. Cell membranes are involved in a

variety of cellular processes such as cell adhesion,ion conductivity andcell signaling

and serve as the attachment surface for several extracellular structures, including the

cell wall,glycocalyx, and intracellularcytoskeleton. Cell membranes can beartificially

reassembled.

Cytoplasm

The cytoplasm comprisescytosol the gel-like substance enclosed within thecellmembrane and the organelles thecell's internal sub-structures. All of the contentsof the cells ofprokaryote organisms (such as bacteria, which lack a cell nucleus) are

contained within the cytoplasm. Within the cells of eukaryote organisms the contents of
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The nuclear membrane is a double-layered structure that encloses the contents of the

nucleus. The outer layer of the membrane is connected to the endoplasmic reticulum.

A fluid-filled space or perinuclear space is present between the two layers of a nuclear

membrane. The nucleus communicates with the remaining of the cell or the cytoplasm

through several openings called nuclear pores. Such nuclear pores are the sites for

exchange of large molecules (proteins and RNA) between the nucleus and cytoplasm.

Chromosomes

Chromosomes are present in the form of strings of DNA and histones (protein

molecules) called chromatin. The chromatin is further classified into heterochromatin

and euchromatin based on the functions. The former type is a highly condensed,

transcriptionally inactive form, mostly present adjacent to the nuclear membrane. On

the other hand, euchromatin is a delicate, less condensed organization of chromatin,

which is found abundantly in a transcribing cell.

Nucleolus

The nucleolus (plural nucleoli) is a dense, spherical-shaped structure present inside the

nucleus. Some of the eukaryotic organisms have nucleus that contains up to four

nucleoli. The nucleolus plays an indirect role in protein synthesis by producing

ribosomes. These ribosomes are cell organelles made up of RNA and proteins; they

are transported to the cytoplasm, which are then attached to the endoplasmic

reticulum. Ribosomes are the protein-producing organelles of a cell. Nucleolus

disappears when a cell undergoes division and is reformed after the completion of cell

division.

CHARACTERISTICS OF LIVIGN ORGANISM

Growth:

The permanent increase in size and dry mass by an increase in number of cells, cell

size, or both.

Irritability

Irritability is an excessive response tostimuli. The term is used for both the

physiological reaction to stimuli and for thepathological, abnormal or excessive

sensitivity to stimuli; It is usually used to refer toanger or frustration.
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Adaptation

An adaptation, also called an adaptive trait, in biology is atrait with a current

functional role in the life history of an organism that is maintained andevolved by

means ofnatural selection.Adaptation refers to both the current state of being

adapted and to the dynamic evolutionary process that leads to the adaptation.

Adaptations contribute to thefitness and survival of individuals.

Metabolism

Metabolism (from Greek:metabol, "change" or Greek:

metabolismos, "outthrow") is the set oflife-sustaining chemical transformations within

the cells of living organisms. These enzyme-catalyzed reactions allow organisms to

grow and reproduce, maintain their structures, and respond to their environments.

Reproduction

Reproduction (or procreation) is thebiological processby which new "offspring"individual organismsare produced from their "parents". Reproduction is a fundamental

feature of all known life; each individual organism exists as the result of reproduction.

The known methods of reproduction are broadly grouped into two main types: sexual

and asexual.

Organization

An organization is asocialentitythat has a collective goal and is linked to an

external environment. The word is derived from the Greek word organon, itself derived

from the better-known word ergon which means "organ" a compartment for aparticular task.

Movement

This allows them to change their position in their environment to obtain essential

requirements such as water, air and food as well as to protect themselves, or locate a

mate.
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Animal Cell Structure