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Organelles in depth

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Cell membrane/Plasma membrane/Lipid bilayer

has 2 layers of lipids (fats); hence aka lipid bilayer.

Often we see simplified 2D drawings, showing a small section of the lipid bilayer.

Here we see the two layers, and some proteins.

 

Cytoplasm

The thick viscous liquid filling the cell. All the organelles float in it; and it’s also filled with millions of enzymes and other chemicals.

Dancing Queen molecules in cytoplasm

Here is a (false color) visualization of proteins in a cell’s cytoplasm – notice how densely packed this is.

Densely packed proteins in cytoplasm

Nucleus

The command-and-control center of the cell.

Chromosomes (made of DNA) are stored in here.

Here we see a more realistic image of the nucleus (lower left); we see mRNA copies of DNA coming out of the nucleus through nuclear pores.

Nucleus to ribosomes to ER GIF Protein synthesis NPR

Nucleus to ribosomes to ER GIF from NPR: Protein synthesis

Chromosomes

If we magnify a cell we see chunks floating in the nucleus called chromosomes. They are made of a chemical called DNA.

organism cell chromosome DNA 2

Here we see a cell nucleus being lysed (broken open) and all the chromosomes are spilling out on the right.

(The color was added by hand to make it easier to tell them apart.)

We can then cut-and-paste each of the chromosomes, number them, and line them up (lower left.)

In humans we find 23 pairs of chromosomes in every cell.

These X shaped chromosomes are not solid; they are like objects made of wound-up yarn.

A chromosome could be unwound into a long, thing string.

This string is made of DNA molecules.

chromosomes 1

Each section of the chromosome has difference sequences of DNA.

A complete sequence of DNA is called a gene; it is an instruction on how to build a protein.

 

Mitochondrion

Plural is mitochondria.

Converts energy from food molecules into a form usable by the cell.

and

 

The Endomembrane system

More details: The endomembrane system is composed of the different membranes that are suspended in the cytoplasm within a eukaryotic cell.

Endomembrane system by Mariana Ruiz Villarreal LadyofHats

Endomembrane system by Mariana Ruiz Villarreal, LadyofHats

Ribosomes

Little organic machines that take in amino acids (from our food) and turn them into proteins.

They are very tiny compared to the size of a cell – often seen as mere dots. 

plant and animal cell ribosomes

Next we see a more realistic 3D model of a cell;

On the right we can just barely see the ribosomes – as small dots stuck to the ER.

On the left we see the ER magnified, and the ribosomes are a bit clearer. (Although we don’t see any details.)

Darryl Leja, NHGRI Rough endoplasmic reticulum and ribosomes

Darryl Leja, NHGRI Rough endoplasmic reticulum and ribosomes

Some ribosomes also float freely in the cytoplasm.

Here we see mRNA copies of DNA coming out of a cell nucleus, and moving to a ribosome floating nearby.

Nucleus to ribosomes to ER GIF Protein synthesis NPR

Nucleus to ribosomes to ER GIF from NPR: Protein synthesis

And now you’ll always remember this:

Beyonce look like the rough ER

 

Cytoskeleton

These thin protein tubes give the cell its shape and mechanical resistance to deformation.

and a photo

 

MCAS question: Structures called microtubules are found in the cytoplasm of most eukaryotic cells. Microtubules are made up of proteins and help shape and support
the cell. Which of the following elements are most abundant in microtubules?

A. lead and zinc .             B. nitrogen and carbon
C. sodium and chlorine .  D. iodine and magnesium

Golgi body

Packages proteins into vesicles inside the cell, and send them to their destination.

Golgi GIF

and here we see the complete system, from nucleus to ER to the Golgi.

Endomembrane system by Mariana Ruiz Villarreal LadyofHats

Endomembrane system by Mariana Ruiz Villarreal, LadyofHats

 

Endoplasmic reticulum

This manufactures lipids and proteins.

Like an assembly line which makes our products

Rough ER GIF

and here we see the ER in a typical animal cell.

Darryl Leja, NHGRI Rough endoplasmic reticulum and ribosomes

Darryl Leja, NHGRI Rough endoplasmic reticulum and ribosomes

 

Lysosome

Contain enzymes that can break down virtually all kinds of biomolecules. Garbage disposal.

Lysosome GIF

Vacuoles

A lipid bag that can store organic molecules.

Vacuole GIF

 

Chloroplasts

Contain a pigment (colored molecule), chlorophyll.

It captures the energy in light.

Transforms that energy into chemical energy, e.g. ATP  and sugar molecules.

 

Here we see a single chloroplast, vastly magnified with a TEM (transmission electron microscope.) We see that there is quite a bit of detail within them.

Chloroplast structure Thylakoid Granum

Cell wall

Note that animal cells don’t have this organelle. Only plants and bacteria have it.

Made of cellulose – a special sugar used to provide structure, and not used for energy.

If the cell membrane is like a balloon, then the cell wall is like a cardboard box around the balloon, protecting it.

Gives strength and support. Allows plants like bamboo and trees to grow tall.

Animal cell versus plant cell

Here we see a typical boxy shaped plant cell, clearly showing the cell wall (green) and the lipid bilayer (yellow, aka plasma membrane.)

Plant cell has a wall adapaproject

Plant cell has a wall adapaproject

 

Large central vacuole

A membrane that stores watery bags of food or waste molecules.

 

Sample questions

Feb 2016 MCAS: Which of the following types of organisms have cell walls composed of cellulose?

A. amoebas     B. birds    C. grasses        D. worms

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Feb 2016 MCAS.  Antibiotics are medicines used to treat bacterial infections in humans. Some antibiotics work by interfering with the bacteria’s ribosomes. Other antibiotics work by interfering with the bacteria’s plasma membrane.

a. Describe the function of the ribosomes and explain why interfering with the ribosomes would kill the bacteria.

b. Describe the function of the plasma membrane and explain why interfering with the plasma membrane [lipid bilayer] would kill the bacteria.

Medicines called antifungals are used to treat infections caused by fungi. One way antifungals work is by targeting cell parts that are present in fungal cells but not in human cells.

c. Identify one cell part other than a ribosome or a plasma membrane that human cells and fungal cells have in common.

d. Describe what would happen to a human cell if the cell part you identified in part (c) were affected by an antifungal. Explain your answer based on the function of the cell part.

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External resources

http://www.amoebasisters.com/gifs.html

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