Animal Cell Model Diagram Project Parts Structure Labeled Coloring and Plant Cell Organelles Cake: A Typical Animal Cell Animal Cell Model Diagram Project Parts Structure Labeled Coloring and Plant Cell Organelles Cake

Wednesday, March 12, 2014

A Typical Animal Cell Animal Cell Model Diagram Project Parts Structure Labeled Coloring and Plant Cell Organelles Cake

A Typical Animal Cell Biography

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Chapter 1: An Owner's Guide to the Cell

By Alisa Zapp Machalek

A typical animal cell, sliced open to reveal cross-sections of organelles.

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Welcome! I hope the transformation wasn't too alarming. You have shrunk down to about 3 millionths of your normal size. You are now about 0.5 micrometers tall (a micrometer is 1/1000 of a millimeter). But don't worry, you'll return to your normal size before you finish this chapter.

At this scale, a medium-sized human cell looks as long, high, and wide as a football field. But from where we are, you can't see nearly that far. Clogging your view is a rich stew of molecules, fibers, and various cell structures called organelles. Like the internal organs in your body, organelles in the cell each have a unique biological role to play.

Now that your eyes have adjusted to the darkness, let's explore, first-hand and up close, the amazing world inside a cell.

Nucleus: The Cell's Brain

Cell Membrane: Specialist in Containing and Communicating

Endoplasmic Reticulum: Protein Clothier and Lipid Factory

Rx: Ribosome Blockers

Golgi: Finishing, Packaging, and Mailing Centers

Lysosomes: Recycling Centers and Garbage Trucks

Mitochondria: Cellular Power Plants

Cytoskeleton: The Cell’s Skeleton...and More

Golgi Spelunking: Exit Here, There, But Not Anywhere

The Tour Ends Here

Morphing Mitochondria

Cool Tools for Studying Cells

Light Microscopes: The First Windows Into Cells

Electron Microscopes: The Most Powerful of All

Studying Single Molecules: Connecting the Quantum Dots

Computers Clarify Complexity

Science Schisms

Got It?

Nucleus: The Cell's Brain

NucleusNuclear Pores

Nucleus

Look down. Notice the slight curve? You're standing on a somewhat spherical structure about 50 feet in diameter. It's the nucleus—basically the cell's brain.

The nucleus is the most prominent organelle and can occupy up to 10 percent of the space inside a cell. It contains the equivalent of the cell's gray matter—its genetic material, or DNA. In the form of genes, each with a host of helper molecules, DNA determines the cell's identity, masterminds its activities, and is the official cookbook for the body's proteins.

Go ahead—jump. It's a bit springy, isn't it? That's because the nucleus is surrounded by two pliable membranes, together known as the nuclear envelope. Normally, the nuclear envelope is pockmarked with octagonal pits about an inch across (at this scale) and hemmed in by raised sides. These nuclear pores allow chemical messages to exit and enter the nucleus. But we've cleared the nuclear pores off this area of the nucleus so you don't sprain an ankle on one.

If you exclude the nucleus, the rest of the cell's innards are known as the cytoplasm.

Eukaryotic Cells Prokaryotic Cells

The cells of “complex” organisms, including all plants and animals “Simple” organisms, including bacteria and blue-green algae

Contain a nucleus and many other organelles, each surrounded by a membrane (the nucleus and mitochondrion have two membranes) Lack a nucleus and other membrane-encased organelles

Can specialize for certain functions, such as absorbing nutrients from food or transmitting nerve impulses; groups cells can form large, multicellular organs and organisms Usually exist as single, virtually identical cells

Most animal cells are 10–30 micrometers across, and most plant cells are 10–100 micrometers across Most are 1–10 micrometers across

Virtually all forms of life fall into one of two categories: eukaryotes or prokaryotes.

Cell Membrane: Specialist in Containing and Communicating

The membrane that surrounds a cell is made up of proteins and lipids. Depending on the membrane’s location and role in the body, lipids can make up anywhere from 20 to 80 percent of the membrane, with the remainder being proteins. Cholesterol, which is not found in plant cells, is a type of lipid that helps stiffen the membrane.

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You may not remember it, but you crossed a membrane to get in here. Every cell is contained within a membrane punctuated with special gates, channels, and pumps. These gadgets let in—or force out—selected molecules. Their purpose is to carefully protect the cell's internal environment, a thick brew (called the cytosol) of salts, nutrients, and proteins that accounts for about 50 percent of the cell's volume (organelles make up the rest).

The cell's outer membrane is made up of a mix of proteins and lipids (fats). Lipids give membranes their flexibility. Proteins transmit chemical messages into the cell, and they also monitor and maintain the cell's chemical climate. On the outside of cell membranes, attached to some of the proteins and lipids, are chains of sugar molecules that help each cell type do its job. If you tried to bounce on the cell's outer surface as you did on the nuclear membrane, all these sugar molecules and protruding proteins would make it rather tricky (and sticky).

Endoplasmic Reticulum: Protein Clothier and Lipid Factory

If you peer over the side of the nucleus, you'll notice groups of enormous, interconnected sacs snuggling close by. Each sac is only a few inches across but can extend to lengths of 100 feet or more. This network of sacs, the endoplasmic reticulum (ER), often makes up more than 10 percent of a cell's total volume.

The endoplasmic reticulum comes in two types: Rough ER is covered with ribosomes and prepares newly made proteins; smooth ER specializes in making lipids and breaking down toxic molecules.Smooth ER

The endoplasmic reticulum comes in two types: Rough ER is covered with ribosomes and prepares newly made proteins; smooth ER specializes in making lipids and breaking down toxic molecules.

Take a closer look, and you'll see that the sacs are covered with bumps about 2 inches wide. Those bumps, called ribosomes, are sophisticated molecular machines made up of more than 70 proteins and 4 strands of RNA, a chemical relative of DNA. Ribosomes have a critical job: assembling all the cell's proteins. Without ribosomes, life as we know it would cease to exist.

To make a protein, ribosomes weld together chemical building blocks one by one. As naked, infant protein chains begin to curl out of ribosomes, they thread directly into the ER. There, hard-working enzymes clothe them with specialized strands of sugars.

Rough ER

SUSUMU ITO

Related Link

Inside Life Science Article: The Big, Fat World of Lipids

Now, climb off the nucleus and out onto the ER. As you venture farther from the nucleus, you'll notice the ribosomes start to thin out. Be careful! Those ribosomes serve as nice hand- and footholds now. But as they become scarce or disappear, you could slide into the smooth ER, unable to climb out.

In addition to having few or no ribosomes, the smooth ER has a different shape and function than the ribosome-studded rough ER. A labyrinth of branched tubules, the smooth ER specializes in synthesizing lipids and also contains enzymes that break down harmful substances. Most cell types have very little smooth ER, but some cells—like those in the liver, which are responsible for neutralizing toxins—contain lots of it.

Next, look out into the cytosol. Do you see some free-floating ribosomes? The proteins made on those ribosomes stay in the cytosol. In contrast, proteins made on the rough ER's ribosomes end up in other organelles or are sent out of the cell to function elsewhere in the body. A few examples of proteins that leave the cell (called secreted proteins) are antibodies, insulin, digestive enzymes, and many hormones.

Rx: Ribosome Blockers

In a dramatic technical feat, scientists obtained the first structural snapshot of an entire ribosome in 1999. This more recent image captures a bacterial ribosome in the act of making a protein (the long, straight spiral in the lightest shade of blue). It also shows that–unlike typical cellular machines, which are clusters of proteins (shown here as purple ribbons)–ribosomes are composed mostly of RNA (the large, light blue and grey loopy ladders). Detailed studies of ribosomal structures could lead to improved antibiotic medicines.

IMAGE COURTESY OF HARRY NOLLER

All cellular organisms, including bacteria, have ribosomes. And all ribosomes are composed of proteins and ribosomal RNA. But the precise shapes of these biological machines differ in several very specific ways between humans and bacteria. That's a good thing for researchers trying to develop bacteria-killing medicines called antibiotics because it means that scientists may be able to devise therapies that knock out bacterial ribosomes (and the bacteria along with them) without affecting the human hosts.

Several antibiotic medicines currently on the market work by inhibiting the ribosomes of bacteria that cause infections. Because many microorganisms have developed resistance to these medicines, we urgently need new antibiotics to replace those that are no longer effective in fighting disease.

Using sophisticated imaging techniques like X-ray crystallography, researchers have snapped molecular pictures of antibiotics in the act of grabbing onto a bacterial ribosome. Studying these three-dimensional images in detail gives scientists new ideas about how to custom design molecules that grip bacterial ribosomes even more strongly. Such molecules may lead to the development of new and more effective antibiotic drugs. —Alison Davis

A Typical Animal Cell Animal Cell Model Diagram Project Parts Structure Labeled Coloring and Plant Cell Organelles Cake