Units Within the Metric System


The metric system is the most widely used system of measurement in the world. It is a more universal measurement standard as compared to the customary system used in the United States.
The three basic units of the metric system are the meter, gram, and liter:

The gram measures weight.The meter measures length.The liter measures capacity.

thousands	hundreds	tens	basic unit	tenths	hundredths	thousandths
1000	100	10	1	0.1	0.01	0.001
kilo-	hecto-	deca-	Meter Gram Liter	deci-	centi-	milli-

A millimeter is about how thick a dime is.
A centimeter is how wide one of your fingernails is.
A kilometer is a little more than half of a mile.

From smallest to greatest they range:

Milli-

Centi-

Deci-

Meter Gram Liter

Deca-

Hecto-

Kilo-

Conversion Chart for Measuring Length
1 kilometer (km) = 1000 meters (m)
1 meter = 100 centimeters (cm) = 1000 millimeters (mm)1 millimeter = 1000 micrometers (um) Cells are measured in micrometers
1 micrometer = 1000 nanometers (nm) Ribosomes and molecules are measured in nanometers

This system is based on the decimal system and base units of 10s. There are two ways to convert measurements:
All the measurements can either be multiplied or divided by 10, 100, 1,000, and so on. You can follow these short 3 steps if you are not sure what to do.

1. Count the number of zeros in the number you are multiplying or dividing by.
2. If you are multiplying, move the decimal point this number of places to the right.
3. If you are dividing, move the decimal point this number of place to the left.

Drill and Practice

Write the equivalents.

1) 18 m =_____ cm
2) 167 mm =_____mm
3) 500 kg = _____g
4) 23 dm =_____hm
5) 1,589 dl =_____dm
6) 700 ml =_____kl
7) 5 cm = _____mm

ATour of the Cell


The picture above is the basic structure of a cell. The nucleus of the cell is the control center. It is also were the DNA is housed in 23 pairs of chromosomes. This DNA contains all the information for the synthesis of the entire organism.Within these chromosomes there are about 25,000 genes, which code for more than 100,000 proteins. The DNA can't leave the nucleus so, in a process called transcription, segments of DNA are copied as mRNA( messenger RNA), which leaves the nucleus through nuclear pores.
After the mRNA leaves the nucleus,ribosomes attach to it and translate the sequence of nucleic acids into a sequence of amino acids (a polypeptide, orprotein). Ribosomes are about 20 nm in size and are made up of 65% ribosomal RNA (which was made in the nucleolous, a dark region of the nucleus) and 35% ribosomal protein. A ribosome has two sub units a large sub unit and a small sub unit (both units are shown in the figure below).
These subunits come together at the start codon (AUG) of mRNA. Ribosomes may be free-floating, or may be embedded in the rough endoplasmic reticulum. The endoplasmic reticulum (ER) is a network of tubular canals within the cytoplasm. Proteins are produced by ribosomes on the surface of the rough ER and released into the lumen (interior space) of the rough ER. These proteins are then transported to an ER which lacks surface ribosomes (smooth ER). A small vesicle then pinches off from the smooth ER (with proteins inside) and moves through the cytoplasm to the Golgi apparatus for further processing.
The Golgi looks like a “stack of pancakes” and contains enzymes that modify proteins ("post-translational modifications") and prepares them for transport to their final destination, either inside or outside the cell. The Golgi receives proteins and enzymes from the endoplasmic reticulum and packages them into membrane-bound vesicles. Often these vesicles move to the cell membrane and release their contents to the outside of the cell (exocytosis).
The Golgi also prepares lysosomes, which are "bags" of enzymes.The lysosomes assist in the digestion of ingested cellular materials and in the breakdown of worn-out cell organelles. Certain human white blood cells (WBC’s) have numerous lysosomes so they can efficiently destroy ingested bacteria that they have engulfed (through phagocytosis). Cells also have a cytoskeleton, which is made from filamentous proteins called “actin filaments” and “microtubules.”These filaments and tubules assist in the movement of organelles within the cells, the movement of the cell itself, and act to maintain the cell’s shape. Some cells have cilia, which are used to move materials past the cell. A good example is the cells lining the respiratory tract, which have cilia to beat mucus and dust up and out the trachea. Only one human cell type, sperm, has a flagellum, which is a long whip-like structure used for propulsion of cells.





Mitochondria (Power House)
The mitochondria are organelles that make energy for the cell in the form of ATP. All cells need a continuous supply of ATP, and it is in the mitochondria that this molecule is produced. The energy to make ATP comes from the food we eat, so ultimately this is why we eat. Oxygen is the final electron acceptor in the electron transport chain, which is happening in the inner membrane of the mitochondria, so ultimately this is why we breathe.

The mitochondria is sometimes referred to as the cellular power plant. It has it's own DNA and regenerates on it's own, much like the cell that it's found in. A cell CAN NOT make mitochondria.

CBS News published this interesting article on the role of mitochondrial DNA in aging. By inducing a high rate of mutation in mitochondrial DNA, researchers made mice age prematurely, suggesting that degradation of mitochondrial DNA may be one of the causes of aging (not just a result of aging). [Note: Kevin removed the article and replaced it with the link and this summary paragraph to avoid copyright violations]

Here is a simple way to remember the "power" of Mitochondria ...with some killer background music!!! http://www.youtube.com/watch?v=ceDopmx1Y2g

Structure of a cell membrane
A barrier must be present to prevent the loss of enzymes, nucleotides, and other cellular molecules that are water-soluble. This is because both inside and outside the cell contains water. So the cell membrane is composed of lipids. It is considered semipermeable because it is permeable to water, gas molecules, and lipid-soluble molecules, but impermeable to most other molecules.

Phospholipids

Phospholipids create most of the cell membrane. A phospholipid is both hydrophilic (the polar part which contains the phosphate group) and hydrophobic (the nonpolar part that contains the lipid (fat) group). The hydrophobic parts are attracted to each other so they form together making this a double layer of phospholipid. Hence, the lipid tails are pointing in towards each other while the phosphate heads are pointing out. The membrane is not solid--it has an oily consistency, and embedded proteins float in it like icebergs in the ocean. The plasma membrane is sometimes called the fluid mosaic model--fluid because it is not solid and things can move about in it, and mosaic because it is composed of many small pieces. The way of passage into or out of the cell mainly is due to the transport proteins embedded into the cell membrane.
***If something can dissolve in fat (lipid soluble) it can dissolve through the cell membrane. An example is steroid hormones, which are derived from cholesterol (a fat). Lipid insoluble products need to go through a channel protein to pass through the membrane.

Proteins in the cell membrane

The proteins can move around the cell membrane freely and transport materials in and out of the cell. Not all proteins are transport proteins--many are enzymes, and many are cell receptors. The proteins are not uniformally placed throughout the membrane--rather the distribution is patchy, localized depending on their function. Remember that receptor proteins only respond to certain chemicals. This is important because proteins serve as receptors for neurotransmitter chemicals released by nerve fibers at the synapse, for hormones, and for chemical messengers sent from one cell to another.

Carbohydrates

The carbohydrates of the plasma membrane are mainly attached to the outer surface as glycoproteins and glycolipids. The glycolipids of red blood cells serve to determine the blood type. A major group of identification proteins is made by the expression of the MHC (major histocompatability) gene complex. When they are searching for a "matching donor" for an organ or tissue transplant, they are looking for people who have similar MHC genes (hence, similar cell-surface markers).We are lucky that our red blood cells do not express MHC genes or blood donations would be as complex as donating a kidney. The carbohydrates affect interactions between cells and help keep red blood cells apart.

Cholesterol

Cholesterol mainly just stabilizes the cell membrane and is embedded inside the phospholipid.



Genetic Control
For those of you who may be really blown away by our discussion on genetics, here is a great tutorial from the U of U. It includes a tour of the cell, the basic concepts behind genetics, and how to transcribe and translate a gene.

Transcription is the process through which a DNA sequence is enzymatically copied by an RNA polymerase to produce a complementary RNA. So to say, it is the transfer of genetic information from DNA into RNA. In the case of protein-encoding DNA, transcription is the beginning of the process that ultimately leads to the translation of the genetic code (via the mRNA intermediate) into a functional peptide or protein. The stretch of DNA that is transcribed into an RNA molecule is called a transcription unit. Transcription has some proofreading mechanisms, but they are fewer and less effective than the controls for copying DNA; therefore, transcription has a lower copying fidelity than DNA replication.[1] As in DNA replication, transcription proceeds in the 5' → 3' direction (i.e. the old polymer is read in the 3' → 5' direction and the new, complementary fragments are generated in the 5' → 3' direction). In the case of transcription, the "old polymer" is the DNA template (non-coding) strand. RNA polymerase binds to the 3' end of a gene on the DNA template strand and travels toward the 5' end. In the process, the RNA polymerase synthesizes an RNA molecule from its 5' end to the 3' end. Except for the fact that thymines in DNA are converted to uracils in RNA, the newly synthesized RNA strand will have the same sequence as the coding (non-template) strand of the DNA. For this reason, scientists usually refer to the DNA coding strand when referring to the directionality of genes on DNA, not the template strand. Thus, genes are said to be transcribed in the 5' → 3' direction.

Here is a graphical representation of Transcription
http://www.johnkyrk.com/DNAtranscription.html


Translation is the second process of protein biosynthesis (part of the overall process of gene expression). Translation occurs in the cytoplasm where the ribosomes are located. Ribosomes are made of a small and large subunit which surrounds the mRNA. In translation, messenger RNA (mRNA) is decoded to produce a specific polypeptide according to the rules specified by the genetic code. This is the process that converts an mRNA sequence into a chain of amino acids that form a protein. Translation is necessarily preceded by transcription. Translation proceeds in four phases: activation, initiation, elongation and termination (all describing the growth of the amino acid chain, or polypeptide that is the product of translation). In activation, the correct amino acid (AA) is joined to the correct transfer RNA (tRNA). While this is not technically a step in translation, it is required for translation to proceed. The AA is joined by its carboxyl group to the 3' OH of the tRNA by an ester bond. When the tRNA has an amino acid linked to it, it is termed "charged". Initiation involves the small subunit of the ribosome binding to 5' end of mRNA with the help of initiation factors (IF), other proteins that assist the process. Elongation occurs when the next aminoacyl-tRNA (charged tRNA) in line binds to the ribosome along with GTP and an elongation factor. Termination of the polypeptide happens when the A site of the ribosome faces a stop codon (UAA, UAG, or UGA). When this happens, no tRNA can recognize it, but releasing factor can recognize nonsense codons and causes the release of the polypeptide chain. The capacity of disabling or inhibiting translation in protein biosynthesis is used by antibiotics such as: anisomycin, cycloheximide, chloramphenicol, tetracycline, streptomycin, erythromycin, puromycin etc.

Review Questions

1. The ___________ is also known as the "cellular power plant".
a. ribosome
b. mitochondria
c. golgi complex
d. nucleus
e. endoplasmic reticulum


2. Neurotransmitters are released from the ends of nerve cells are an example of what process?

a. phagocytosis
b. pinocytosis
c. endocytosis
d. exocytosis




3. Cassy the red blood cell went to a physiwiki party and after chatting with the other cells at the party she realized she was out of place and extremely different. Cassy realized the other cells were all under control and that she was lacking a nucleus. This means that Cassy is what?
a. a eukaryote
b. a ribosome
c. a prokaryote
d. a wileEcoyote
[Please see Kevin's comment on this question on the page with answers]

4. After floating around the cell for days the floating solid material was snatched up by the cell and taken inside. This is a process called?
a. excoytosis
b. pinocytosis
c. phagocytosis
d. absorption

5. The cells proteins and lipids are planning to leave the cell. In order for a safe trip outside the cell they must be packaged properly, where do they need to go inside the cell to accomplish this?
a. golgi apparatus
b. vacuoles
c. mitochondria
d. endoplasmic reticulum

6. How many different types of RNA are there?
a. 5
b. 6
c. 3
d. 2
e. 4

7. The term genome can refer to:
a. all the genes in a particular individual
b. only one gene in an individual
c. all the genes in a particular species
d. both a and c
e. none of the above

8. Which of the following is not a function of protein in the cell membrane?
a. structural support
b. synthesis of DNA
c. enzymatic control of chemical reactions
d. receptors for hormones and other arriving regulatory molecules

9. Which of the following organic molecules is not commonly found in the cell membrane?
a. carbohydrates
b. protein
c. cholesterol
d. nucleic acids

10. Which of the following molecules cannot pass through nuclear pores?
a. water
b. potassium ions
c. glycerol
d. DNA