Friday, 3rd October 2014, 7th Microbiology Class "Eid al-Adha"

Everyone was in the mood of going back home today, with their bags (please notice the (s) on the bag hahaha indicating they are carrying more bags than they usually do to class) I wish you Happy Eid al-Adha in advance :) I hope all of you arrived home safely. 

Today's lesson continues from where we last stop last week. Still under the topic of external structures of prokaryotes before proceeding on some of "The Internal structures of Prokaryotes". Despite the "Raya" mood, everybody was cooperating with the lesson as usual. Hehe. And we even had some foods mentioned during class! It's not even related to Raya actually. It's all because we came across the diagrams of peptidoglycan that looks a lot like sausages, Gram negative and Gram positive cell walls that look like spaghetti with meatballs and cytoplasm, due to it's jellylike structure, it reminds everyone of jelly or in malay we called it 'dadih'. Hahahaha. I see all of you are hungry, eh? x'D

"Spaghetti and meatballs" Gram negative and Gram positive cell walls

"Sausages" peptidoglycan 

Today Dr Wan kind of focusing more on the Gram positive and Gram negative cell walls during the end of the lesson. Thus, I shall conclude about these cell walls first.

The two cell walls are different are different by the structure itself. Like the one that I have posted above. 

GRAM POSITIVE CELL WALL 

1. 1- Have many layers of peptidoglycan. 
2. 2- Contains teichoic acid and lipoteichoic acid (which is teichoic acid that attached to plasma membrane) 
3. 3- 90% of the cell wall is peptidoglycan. 
4. 4- Do not contain outer membrane. 

FUN FACT #1

Teichoic acid

• There are two types : wall teichoic acid (WTA) that attached to peptidoglycan and lipoteichoic acid (LTA) that attached to plasma membrane.
• Resistance towards environmetal stresses, low osmolarity, antimicrobial peptides, antimicrobial fatty acids, cationic antibiotics and lytic enzymes produced by the host. 
• Act as receptor for phage particles. 
• Can bind to cationic groups thus providing a reservoir of ions close to the surface of bacteria that may ease the activity of different enzymes. 
• Involved in cell division and cell morphogenesis (a process that concerned with the shapes of tissues, organs and entire organisms and the positions of the various specialized cell types).
• WTA act as the spatial and temporal regulator for peptidoglycan metabolism, controlling the level of cross-linking. The highly cross-linked peptidoglycan showed a higher resistance to enzymatic degradation by lysozyme. 
• Thus, the high resistance helped the bacteria when interacting with host that produce lysozyme as they can defense themselves against bacterial infections. 
• And also, the cell wall does not degrade easily! 
• Hence, that's why most of Gram positive bacteria are not pathogenic; harmless.

GRAM NEGATIVE CELL WALL 

1. Very few layer of peptidoglycan. 
2. Have outer membrane that consists of lipoproteins, lipopolysaccharides (LPS), phospholipids and porins. 
3. 10% of the cell wall is peptidoglycan.

Aside from Gram positive and Gram negative cell wall, there are also atypical cell walls. Which 'atypical' itself means 'unusual'. 

ATYPICAL CELL WALL (Unusual cell wall) 

1. Mycoplasma : Have no cell wall. Instead, they have sterols. (which has the same composition with cholesterol). 
2. Chlamydiaceae : The cell wall contains LPS.
3.  Archaea : Lack of peptidoglycans in their cell walls but have pseudopeptidoglycans. 

THE DIFFERENCE BETWEEN CELL WALL OF AN ARCHAEA AND BACTERIA

As I had mentioned in the previous entry. The difference between archaea and bacteria is the components of their cell wall where peptidoglycan is present in bacteria but not in archaea.

Instead, archaea have pseudopeptidoglycan which is a substance that is quite similar to peptidoglycan.

The difference between peptidoglycan and pseudopeptidoglycan is that in peptidoglycan, the disaccharide molecule is made up of monosaccharides called N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM). The alternating NAM and NAG molecules are linked by β(1,4) glycosidic bonds.

On the other hand, pseudopeptidoglycan in archaea are made up of N-acetylglucosamine (NAG) which is the same as in peptidoglycan, but instead of NAM, it has N-acetyltalosamimuronic acid (NAT).  The alternating NAM and NAT are linked by β(1,3) glysodic bonds.

Next, we proceeded on the “Internal Structures of Prokaryotes”. During this “session”, the class participated more when discussing/learning this topic, there were more response compared to when Dr Wan was teaching us about the “External Structures of Prokaryotes”. It’s obvious that this is all because of our previous assignment Dr Wan assigned us last week -->> Make a mind map for the topic of internal structures of prokaryotes.

The internal structures of prokaryotes consists of

• Plasma membrane
• Cytoplasm
• The nuclear area (Nucleoid and plasmid)
• Ribosomes
• Inclusions
• Endospore

FUN FACT #2

Prokaryotes do carry on respiration. There are two types of respiration which are aerobic respiration and anaerobic respiration.  The plasma membrane is the one who is responsible to carry on the respiration, though. 

PLASMA MEMBRANE

There are two movements of materials across the membrane namely the active process and passive process.

PASSIVE PROCESS

·    The process where molecules move from a region of higher concentration to a region of lower concentration, down the concentration gradient, WITHOUT the aid of energy (ATP).

·   

T   There are three types of passive process which are simple diffusion (The movement of molecules from high to low concentration until equilibrium), facilitated diffusion (the movement of molecules from high to low concentration, WITH the aid of carrier protein), and osmosis (the movement of water from high concentration of water to low concentration of water).

ACTIVE PROCESS

·    The process where molecules move from a region of lower concentration to a region of higher concentration, against the concentration gradient, WITH the aid of energy (ATP).

·   
     There are two types of active process which are active transport (molecules are moved by transporter protein from low to high concentration, with the aid of energy) and group translocation (where the transport protein change shape when transporting the molecules, with the aid of energy).

CYTOPLASM

This is where we were all reminded to “dadih” due to the jelly-like structure of the cytosol. Haha!

The major substances of cytoplasm are DNA, ribosomes and inclusions.

NUCLEAR AREA

Consists of the nucleoid and plasmid.

NUCLEOID

·    Nucleoid is a single, long circular molecule of double stranded DNA (in prokaryotes, we called it “bacterial chromosome”).

PLASMID

•      Small, circular, double-stranded DNA.
•      An extrachromosomal genetic elements.
•      There are five types of plasmid with their own specific functions which are virulence plasmid, Col plasmid, fertility plasmid, degradative plasmid and resistance plasmid.

The functions of each type of plasmid

•     They are transferable from one bacteria to another bacteria. (same species only!!)

Functions of the plasmid :

1.     To carry antibiotic resistant genes and spread them. Thus, many diseases can be prevented or treated.
2.    To carry genes that involved in metabolic activities.
3.     Capable of producing antibacterial proteins. 

And there are also other functions of plasmid. 

RIBOSOMES

In my opinion, ribosome is an organelle that is very well known to everyone.  For  “everyone” that previously studied Biology/Science in secondary school, that is. Hehe.

The function of ribosome is as the site of protein synthesis. And they are one of the major components of cytoplasm, as I had mentioned earlier. In eukaryotes, some ribosome are membrane bound (where they are attached to the rough endoplasmic reticulum (RER) and some are boundless, and floating around in the cytosol). Since there are no RER in prokaryotes, the ribosomes are pretty much boundless.

There are 70S (S = Svedberg unit) ribosomes which consists of two subunits, small subunits = 30S and large subunits = 50S).

If you’re wondering why 30S and 50S doesn’t make up a total of 80S but instead of the stated 70S. I did wonder about that too, but sadly I didn’t do any initiatives to look up for it. Hee. I’ll be more productive and curious after this. I will!! And. Ah. Actually Dr Wan asked us during today’s class. “Anybody searched for why it 70S and not 80S?” but nobody answered. Hehe. 

Dr Wan said that it is because during centrifugation, there are some ribosomes that are lost, that’s why the number of ribosomes are not enough (80S).

In conclusion, cells that have a high rates of protein  synthesis, obviously have a large number of ribosomes inside them. Thus, several antibiotics will get into action in order to inhibit protein synthesis of ribosomes.

Some examples of the antibiotics are :

•      Aminoglycoside antibiotic (streptomycin, gentamicin, azithromycin, telithromycin etc) 
•      Macrolide antibiotics (Erythromycin, clarithromycin etc….)

FUN FACT #3

Macrolides are primarily bacteriostatic, that is by binding to 50S subunits of the ribosome, they inhibit bacterial protein synthesis. 

"Bacteriostatic" = Capable of inhibiting the growth or reproduction of bacteria. 

And today’s class ended!! Three days of holiday, is quite long…  I mean, Dr Wan said that it is long.. I… have no comment on that. Hahaha. What I do know is, I can’t wait to go home! Salam Eid al-Adha everyone! 

P/S  Although today’s lesson went well, and I understand most of it but there are some that I don’t understand, especially on the Gram positive and Gram negative part. Since there are Gram positive and Gram negative cell walls for both bacteria and archaea. It is quite confusing at first, i didn’t know that there are also Gram positive and Gram negative archaea too!! I’m surprised when I found out that in the lecture notes. Haha.. I will read more on that, read carefully. Real careful. Hmm but come to think of it, it’s not that I don’t understand. I’m confused. Hehe...