Chapter 3 cells

Chapter 3: Cells

© 2013 John Wiley & Sons, Inc. All rights reserved.

Cells A GENERALIZED VIEW OF THE CELL THE PLASMA MEMBRANE TRANSPORT ACROSS THE PLASMA

MEMBRANE CYTOPLASM NUCLEUS GENE ACTION: PROTEIN SYNTHESIS SOMATIC CELL DIVISION CELLULAR DIVERSITY AGING AND CELLS


A Generalized View of the Cell Cells vary greatly in size, shape and function,

but all cells have common features and components

All cells have three main regions Nucleus Cytoplasm – cytosol and organelles Plasma membrane


A Generalized View of the Cell



Anatomy Overview:

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• Cell Structure and Function

The Plasma Membrane Selectively permeable – permits some substances to

cross more easily than others Primarily lipid barrier that surrounds and contains the

cytoplasm of a cell Lipid barrier consists of two back to back phospholipid

layers Lipid bilayer contains numerous proteins

Integral proteins extend through membrane Peripheral proteins found on one surface

Membrane proteins function as channels, receptors and cell identity markers


The Plasma Membrane



Anatomy Overview:


• Plasma Membrane Structure

Transport Across the Plasma Membrane Membrane transport – substance movement

into or out of the cell Two general methods of transport

____ transport – no energy required ____ transport – cell must use energy (ATP)

The plasma membrane allows some substances to move into and out of the cell but restricts the passage of other substances This property of membranes is called _____


Transport Across the Plasma Membrane Membrane transport – substance movement

into or out of the cell Two general methods of transport

Passive transport – no energy required Active transport – cell must use energy (ATP)

The plasma membrane allows some substances to move into and out of the cell but restricts the passage of other substances This property of membranes is called selective

permeability


Transport Across the Plasma Membrane ____ (ICF) – fluid in body cells ____ (ECF) – fluid outside body cells ____ fluid – ECF between cells in tissues ____ – ECF in blood vessels ____ – ECF in lymphatic vessels ____ – any material dissolved in a fluid ____ – fluid that dissolves materials


Transport Across the Plasma Membrane Intracellular fluid (ICF) – fluid in body cells Extracellular fluid (ECF) – fluid outside body

cells Interstitial fluid – ECF between cells in tissues Plasma – ECF in blood vessels Lymph – ECF in lymphatic vessels Solute – any material dissolved in a fluid Solvent – fluid that dissolves materials


Transport Across the Plasma Membrane – Diffusion The selective permeability of the plasma membrane supports the existence

of concentration gradients, differences in the concentration of chemicals between one side of the membrane and the other.

Diffusion is the movement of substances due to their kinetic energy. In net diffusion, substances move from an area of higher concentration to an area of lower concentration until equilibrium is reached. At equilibrium the concentration is the same throughout the solution.

In simple diffusion, lipid-soluble substances move through the lipid bilayer. In facilitated diffusion, substances cross the membrane with the assistance of ion channels and carriers.


Transport Across the Plasma Membrane – Osmosis

Osmosis is the movement of water molecules through a selectively permeable membrane from an area of higher water concentration to an area of lower water concentration. In an isotonic solution, red blood cells maintain their normal shape; in a hypotonic solution, they gain water and undergo hemolysis; in a hypertonic solution, they lose water and undergo crenation.


Transport Across the Plasma Membrane – Vesicular Transport Transport in vesicles includes both endocytosis

(phagocytosis and bulk-phase endocytosis [pinocytosis]) and exocytosis. Phagocytosis is the ingestion of solid particles. It is an important process used by some white blood cells to destroy bacteria that enter the body. Bulk-phase endocytosis is the ingestion of extracellular fluid. Exocytosis involves movement of secretory or waste products out of a cell by fusion of vesicles within the cell with the plasma membrane.


Transport Across the Plasma Membrane – Passive Processes


Diffusion – particles distribute themselves evenly (homogenously) within a solution moving from high concentration to low concentration









Transport Across the Plasma Membrane


Transport Across the Plasma Membrane – Active Processes Active processes are required when

materials are unable to pass through the cell membrane by diffusion e.g. too large, unable to dissolve in the fat core of

the membrane, or have to move up a concentration gradient


Transport Across the Plasma Membrane – Active Processes



Animation:


• Transport Across the Plasma Membrane

Transport Across the Plasma Membrane – Active Processes


Transport Across the Plasma Membrane


Cytoplasm

Cytoplasm includes all the cellular contents between the plasma membrane and nucleus; it consists of cytosol and organelles.

Organelles are specialized cellular structures with characteristic shapes and specific functions.


Cytoplasm – Cytoskeleton

The cytoskeleton is a network of several kinds of protein filaments that extend throughout the cytoplasm; they provide a structural framework for the cell and generate movements. Components of the cytoskeleton include microfilaments, intermediate filaments, and microtubules.


Cytoplasm – Cytoskeleton


Provides a framework for cellular shape and organization

Functions in internal and external cellular movement

Cytoplasm – Centrosome

The centrosome is an organelle that consists of two centrioles and pericentriolar material. The centrosome serves as a center for organizing microtubules in interphase cells and the mitotic spindle during cell division.


Cytoplasm – Centrosome


Forms a scaffold essential for duplication of cellular DNA during cellular division

Cytoplasm – Ribosomes

Ribosomes, composed of ribosomal RNA and ribosomal proteins, consist of two subunits and are the sites of protein synthesis.




Synthesize all _______



Synthesize all proteins

Cytoplasm – Endoplasmic Reticulum Endoplasmic reticulum (ER) is a network of membranes that

extends from the nuclear envelope throughout the cytoplasm. Rough ER is studded with ribosomes. Proteins synthesized on the ribosomes enter the ER for processing and sorting. The ER is also where glycoproteins and phospholipids form.

Smooth ER lacks ribosomes. It is the site where fatty acids and steroids are synthesized. Smooth ER also participates in releasing glucose from the liver into the bloodstream, inactivating or detoxifying drugs and other potentially harmful substances, and storing and releasing calcium ions that trigger contraction in muscle cells.


Cytoplasm – Endoplasmic Reticulum ______ER –

studded with ribosomes to synthesize proteins embedded in membranes

______ER – involved in calcium regulation, lipid synthesis & detoxification


Cytoplasm – Endoplasmic Reticulum Rough ER –

studded with ribosomes to synthesize proteins embedded in membranes

Smooth ER – involved in calcium regulation, lipid synthesis & detoxification


Cytoplasm – Golgi Complex

The Golgi complex consists of flattened sacs called cisterns that receive proteins synthesized in the rough ER. Within the Golgi cisterns the proteins are modified, sorted, and packaged into vesicles for transport to different destinations.

Some processed proteins leave the cell in secretory vesicles, some are incorporated into the plasma membrane, and some enter lysosomes.


Cytoplasm – Golgi Complex

Modifies proteins

Forms secretory vesicles


Cytoplasm – Mitochondria

Mitochondria consist of a smooth outer membrane, an inner membrane containing folds called mitochondrial cristae, and a fluid-filled cavity called the matrix. They are called “powerhouses” of the cell because they produce most of a cell’s ATP.


Cytoplasm – Mitochondria Powerhouses of

the cell that form most cellular ___


Cytoplasm – Mitochondria Powerhouses of

the cell that form most cellular ATP


Cytoplasm – Lysosomes, Peroxisomes, and Proteasomes Lysosomes are membrane-enclosed vesicles that contain digestive

enzymes. They function in digestion of worn-out organelles (autophagy) and even in digestion of their own cell (autolysis).

Peroxisomes are similar to lysosomes but smaller. They oxidize various organic substances.

Proteasomes contain proteases that continually degrade unneeded, damaged, or faulty proteins.


Cytoplasm


Cytoplasm


Nucleus The nucleus consists of a double nuclear envelope; nuclear pores, which control the

movement of substances between the nucleus and cytoplasm; nucleoli, which produce ribosomes; and genes arranged on chromosomes.

Most body cells have a single nucleus; some (red blood cells) have none, and others (skeletal muscle cells) have several.

Genes control cellular structure and most cellular functions.


Master control center of the cell that contains hereditary genetic material (DNA)

Gene Action – Protein Synthesis


Gene Action – Protein Synthesis ___________ –

process by which a RNA copy (messenger RNA or mRNA) of a DNA gene is produced


Gene Action – Protein Synthesis Transcription –

process by which a RNA copy (messenger RNA or mRNA) of a DNA gene is produced


Gene Action – Protein Synthesis Translation – process by which a messenger

RNA is “read” in order to manufacture the corresponding protein


Gene Action – Protein Synthesis








Gene Action – Protein Synthesis Most of the cellular machinery is devoted to protein synthesis.

Cells make proteins by transcribing and translating the genetic information encoded in the sequence of four types of nitrogenous bases in DNA.

In transcription, genetic information encoded in the DNA base sequence (base triplet) is copied into a complementary sequence of bases in a strand of messenger RNA (mRNA) called a codon. Transcription begins on DNA in a region called a promoter.


Gene Action – Protein Synthesis Translation is the process in which mRNA associates

with ribosomes and directs synthesis of a protein, converting the nucleotide sequence in mRNA into a specific sequence of amino acids in the protein.

In translation, mRNA binds to a ribosome, specific amino acids attach to transfer RNA (tRNA), and anticodons of tRNA bind to codons of mRNA, bringing specific amino acids into position on a growing protein.

Translation begins at the start codon and terminates at the stop codon.



Animation:


• Protein Synthesis

Somatic Cell Division Cell division is the process by which cells reproduce themselves. Cell division

that results in an increase in the number of body cells is called somatic cell division; it involves a nuclear division called mitosis plus division of the cytoplasm, called cytokinesis.

Cell division that results in the production of sperm and oocytes is called reproductive cell division.

The cell cycle is an orderly sequence of events in somatic cell division in which a cell duplicates its contents and divides in two. It consists of interphase and a mitotic phase.

During interphase, the DNA molecules, or chromosomes, replicate themselves so that identical chromosomes can be passed on to the next generation of cells. A cell that is between divisions and is carrying on every life process except division is said to be in interphase.


Somatic Cell Division

Mitosis is the replication and distribution of two sets of chromosomes into separate and equal nuclei; it consists of prophase, metaphase, anaphase, and telophase.

During cytokinesis, which usually begins late in anaphase and ends in telophase, a cleavage furrow forms and progresses inward, cutting through the cell to form two separate identical cells, each with equal portions of cytoplasm, organelles, and chromosomes.


Somatic Cell Division








Cellular Diversity

The different types of cells in the body vary considerably in size and shape.

The sizes of cells are measured in micrometers. One micrometer (µm) equals 10-6 m (1/25,000 of an inch). Cells in the body range from 8 µm to 140 µm in size.

A cell’s shape is related to its function.



Cellular Diversity

Aging and Cells

Aging is a normal process accompanied by progressive alteration of the body’s homeostatic adaptive responses.

Many theories of aging

have been proposed,

including genetically

programmed cessation of

cell division, shortening of

telomeres, addition of glucose

to proteins, buildup of free radicals, and an intensified autoimmune response.


End of Chapter 3

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