Cell Structure

i-710d005c8660d36282911838843a792d-ClockWeb logo2.JPGSecond lecture notes from my BIO101 class (originally from May 08, 2006). As always, in this post and the others in the series, I need comments - is everything kosher? Any suggestions for improvement?

BIO 101 - Bora Zivkovic - Lecture 1 - Part 2

The Cell

All living organisms are composed of one or more cells - the cell is the unit of organization of Life.

Most cells are very small. Exceptions? Ostrich egg is the largest cell. Nerve cell in a leg of a giraffe may be as long as 3m, but is very thin.

Basic Structure of the Cell

A cell is a small packet or bag of liquid. The liquid is cytoplasm (or cytosol), which is essentially salty water with various organic molecules suspended in it.

The cytoplasm is contained within a cell membrane. Cell membrane is a phospholypid bilayer - this means that it is composed of two layers of tighly packed molecules of fat. Within the membrane, proteins are embedded into the bilipid layer and are more or less free to move around within the membrane. These proteins are important for the communication between the inside and outside of the cell.

You can see a good image here.

On the outside of the membrane, some cells may have additional structures. For instance, many bacterial and plant cells have thick cell walls that confer more rigidity to the cell as well as better defense against mechanical, chemical or biological insults.

Some cells also have hair-like cilia on the surface (e.g., a protist called Silver Slipper), or long whip-like flagella at one end (e.g., sperm cells). Both of these structures allow the cell to move utilizing its own energy.

Inside every cell, there is hereditary material - DNA. Exceptions? Red blood cells which have a membrane and cytoplasm, but no hereditary material.

Differences between prokaryotes and eukaryotes:

Prokaryotes (bacteria) have a cell membrane and cytoplasm and no other organelles.
Eukaryotes (plants, animals, fungi, protista) have a number of different cell organelles.

The nuclear material in Prokaryotes is a single, circular strand of DNA.
The nuclear material in Eukaryotes is organized in multiple chromosomes contained with a nucleus.

Cell Organelles

i-762b5917878abf32802084dbcd6f93fb-a2 animal cell.pngEukaryotic cells have organelles. Organelles are subcellular structures that provide internal compartmentalization and other functions.

Nuclues is a large membrane-bound organelle. Its function is to sequester the DNA from the rest of the cell. The nuclear membrane (or nuclear envelope), which is also a phospholipid bilayer, selectively allows molecules to pass between the nucleus and cytoplasm. Inside the nucleus, DNA is organized in chromosomes. A chromosome is a tighly coiled and wound strand of DNA packaged with various proteins (e.g,. histones).

Smooth endoplasmic reticulum is a system of membranes and is involved in carbohydrate and lipid synthesis.

Rough endoplasmic reticulum is a system of membranes that possesses ribosomes. Proteins are synthesized in the rough ER.

Golgi apparatus stores and packages various molecules. When a molecule is needed elsewhere in the cell, a portion of the Golgi membrane closes off and forms a vesicle that can be transported around the cell.

Some eukaryotic organelles contain a little bit of their own DNA: the mitochondria and the chloroplasts. These two organelles used to be intercellular parasites, i.e., different species of bacteria that, over time, became an integral part of a cell.

Chloroplasts are found in plant cells. Photosynthesis is the process that occurs in them.

Mitochondria are found in all Eukaryotic cells. Breakdown of glucose begins in the cytoplasm and ends in the mitochondria, where the final products of the breakdown are ATP, water, CO2 and heat. This process requires oxygen - that is why we breath: to provide the oxygen for the mitochodria and to get rid of carbon dioxide produced in the mitochondria.
i-4b4812479176489e01cec06b6163c6c2-a3 mitochondria.png
ATP (adenosine triphosphate) is the energy currency of the living world. Every cellular process that requires energy gets it from ATP. Thus, mitochondria are sometimes refered to as "factories of the cell".

The final portion of the process of glucose digestion (the Krebs cycle) is, like any process, not 100% efficient. Errors happen and not every atom of every glucose molecule ends up where it should: in ATP, water or CO2. The result of this inefficiency is production of heat and production of highly reactive small molecules called free radicals (e.g., hydrogen peroxyde, H2O2). Free radicals tend to quickly react with whatever molecule they first encounter upon leaving the mitochondria. Such reactions damage those molecules, be they proteins, lipids, sugars or nucleic acids. The intercellular damage caused by free radicals is one aspect of the process of aging.

Some animals - birds and mammals - have harnessed the heat production by the mitochondria to keep a stable internal temperature. The efficiency of the mitochondrial "machine" is held low under the control of hormones like thyroid hormones. As a result, there is a greater production of free radicals, so warm-blooded animals evolved particularly good mechanisms for neutralizing free radicals and for repairing the damage. If a person keeps a constant low temperature or constant low-grade fever, the first thing the physician will check is the function of the thyroid gland.

The cytoskeleton, composed of filaments and microtubules, anchors the organelles and gives a cell its shape. Microtubules move organelles, including vesicles, within a cell. They also move the membrane-embedded proteins around where they are needed.
i-e3a6e122dbadbaf1b9a1e05ab9d358ed-a4 cytoskeleton.jpg


Peter H. Raven, George B. Johnson, Jonathan B. Losos, and Susan R. Singer, Biology (7th edition), McGraw-Hill Co. NY, Chapter 5

Previously in this series:
Biology and the Scientific Method


More like this

this really helped me with my cell project...=)

By Myrna Rodriguez (not verified) on 31 Aug 2007 #permalink

Thanks for the good, simple, fun-fact-filled info. I'll have to direct some of my biology students this way : )

Explain the process of Osmosis and Diffusion in relation to respiration,nutrition and excretion.

the pictures helped explain alot

This was a really good set of notes, however it'd be even better if more of the structures were explained. Thanks for posting it!

Thank you so much! I'm having trouble in my BIO class due to the fact that my teacher is foreign and has a heavy accent and I can't read her handwritting on the board. So, this was wonderful! Thank you so much!

Perhaps when you talk about cells being small, mention why they are small, and what kind of adaptations allow an ostrich egg to seem to "break" the rule.

Friendly asides like that help make things interesting and give students time to absorb the info.

Microtubules don't actively move vesicles about, now do they? I think that is an over-simplification that the students can do without. Besides motor proteins are kind of cool.
Otherwise a very succinct and nice, accurate and good lecture. Thank you.
/4th year undergrad

Your good lecture made me forget why I initially googled into it; I wondered if the ostrich egg contains a nucleus that is in any way bigger than the average mammal stem cell nucleus? Or any other odd cell physiology? Or if the entire size is strictly due to nutritional resources? Would be neat to know.

Thanks very much for posting this blog it was very helpful and had lots of interesting/helpful information. it helped me do my science model:)

This was a lot of help on my report. BTW, Ilunga, Diffusion is when molecules move through a membrane from an area of high concentration to an area of low concentration, and osmosisis when it happens with water.

very good for student university of laos

By noum and hum (not verified) on 20 Dec 2007 #permalink

i like the pretty picture it is nice

By dane train (not verified) on 06 Jan 2008 #permalink

Thanks, it helped me do my homework when i had nothing else to look at

O thx alot. this is everything what i needed to here.

This is a great help but you could add more to it!! If u need any help than i would happily help u with it!

tiz reali helpz me in my bio studiez..

yo...i was doin a cell project for school and i used this diagram...the only problem was that it doesnt have many of the parts i need...sorry but i didnt read it...i am doing this project...last minute...

By madison kirby (not verified) on 26 Feb 2008 #permalink

This is a fantastic diagram and the info is really good...its helping me with my biology assingment for college!

can you please tell me what ATP stands for?

>> can you please tell me what ATP stands for?

Yikes. Isn't it spelled out literally right next to it in the above paragraph?
ATP (adenosine triphosphate) is the energy currency of the living world...

>> yo...i was doin a cell project for school and i used this diagram...the only problem was that it doesnt have many of the parts i need...sorry but i didnt read it...i am doing this project...last minute...

Really? Well, let's cater the whole intarwebs to idiots that can't bother to read a few pages of text, and then bitch because the diagram they stole wasn't perfect.

Coturnix, you have infinite patience. I sincerely appreciate these notes, as I am re-boning up on my bio to go back to school next fall and am interested in biology. Any advice? I graduated a few years ago with an English degree (stop throwing things at me, please.) and find it to be worthless, more or less. And I've recently become more in touch with my childhood love of science. Thank you again, and I apologize for the plethora of idiots who seem to propagate the webs.

super.more usefull for usmle

By kanakaraju (not verified) on 25 Apr 2008 #permalink

tanx this website is very legite and has some really excellant information on the organelle of a animal cell

what type of cell is it?????????????????????????????

By gabrielle bella (not verified) on 16 Jun 2008 #permalink

yowzaz, this site blew my mind, i didnt know that there was so much to know about cells. wow i didnt know that the Mitochondria are found in all Eukaryotic cells.fyi get another picture

By beavus franklin (not verified) on 22 Jul 2008 #permalink

I am helping my child do an animal cell project. We need to label a chromosome of an animal cell. I haven't found it anywhere on the internet. Help us please!

Thanks a lot! I am a first-time Biology teacher. This will simplify the topic for my students.

By Marian Tantingco (not verified) on 25 Aug 2008 #permalink

REMOTE CONTROL by DNA as a Bio-piezoelectric -Antenna.

"Piezoelectric quantum transduction is a fundamental property of at distance induction of genetic control "

Remote control of Nuclear-DNA is determined by the piezoelectric changes in response to structural modification in shape and lengths of the double helix during the formation of RNA copies.

More info in www.wbabin.net Paolo Manzelli pmanzelli@gmail.com

what about lysosomes

i was wondering if you could send me some more pics of diff kinds of cells
i am doing a project for a report for school that would be great

this is fantastic helped me do my college work thanks alot.
I was woundering wether there is more on cell organelles ?

i have no fuckin idea what a cytoskeleton and this website did not help no one fuckin bit.

What about vacuoles?

I was wondering wich is bigger, the nucleus or the chloroplast?
Also, you spelled nucleus wrong in the bold heading for "nucleus" as "nuclues".
and I really like your shirt! (the "I am away from my computer right now")

Thanks a lot!! Wonderful description.

yay nerds

I would like to reproduce in our book the figure showing cell organells from your blog. The book is about DNA Fingerprinting, and is aimed at students and common public for educational purpose. Appropriate credit line will be incuded. Please respond. Urgent.

By M W Pandit (not verified) on 29 May 2009 #permalink


Each and every one of the trillions of cells in the body has to defend themselves. And the most important celluar component inside every cell that protects all cell components you failed to show.

it is pretty cool

Nicely done. Well worded for adult students who typically have difficulty understanding cellular structure or the importance of knowing it. The only typo I saw was under mitochondria...it should read "it is why we breathE." (not breath). :-)

This made my exams so easy. So thank you!!!

By Jeremy Monreal (not verified) on 14 Dec 2009 #permalink

please someone send me more pictures to my email of the euand pro kary. i need them for school.

can tell us wat is d function found inside d SELL?

By mark ocampo (not verified) on 17 Jul 2010 #permalink