1st course, Bacteria

Structure of a Bacteria

If we look at the structure of bacteria we will find:

Life Processes

Bacteria are alive, as they conduct all of the functions of life

These functions are: MRSGREN

Movement - move something

Reproduction - make more of your type

Sensitivity - sense something

Growth - get bigger

Respiration - break down compounds for energy

Excretion - get rid of waste compounds

Nutrition - eat atoms 

Movement

The main way that bacteria move is with their flagella

The Flagella is like a tail

The bacteria whip it around, causing motion

Reproduction

Binary Fission 

Binary Fission is the main form of bacteria reproduction

The bacteria eats, grows, gets to its maximum size, copies its DNA, moves its DNA to either side of its cell, then splits in half

The cell that splits is called the 'parent' cell

The new cells are called 'daughter' cells

These daughter cells have identical DNA, so they are all the same

These daughter cells are genetic clones of the parent cell

This is asexual reproduction

Asexual reproduction only uses one parent. The offspring are clones, because there is no exchange of DNA

When there is an abundance of food, binary fission will allow the bacterial numbers to grow very rapidly.

This is because for each parent cell, there will be 2 daughter cells. 

So, bacterial numbers double quickly: 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192. We'll stop at this 13th generation.

By the 20th generation we have crossed 1,000,000 and by the 30th generation we cross the billion mark. 

Because bacteria are so small, it doesn't take them long to eat enough atoms to double in size and then divide. 

It we take a hypothetical number of 1 generation per hour, then by the second day the numbers of bacteria are in the billions

In ideal conditions, some bacteria can grow and divide every 20 minutes!

Yoghurt bacteria

Bacterial Growth Curves 

The reproduction of bacteria can be charted on a 'growth of colony' graph, known as: Bacterial Growth Curves 

Be aware that these Bacterial Growth Curves chart the growth of the colony not of individual bacteria

With these Bacterial Growth Curves there are 4 phases: Lag, Exponential, Stationary, Death.

The colony growth takes a while to start, this is because the bacteria must release enzymes to digest the agar, and then it must absorb the nutrients. This lag at the start of population growth is called the 'lag stage'

As the nutrients become available from the extracellular digestion, the numbers skyrocket. The population increases exponentially. This phase is called the exponential phase.

Finally the abundance of nutrients reduces as they are digested and absorbed. Here we have a stationary phase, where the number of bacteria dying due to starvation are equal to the number that still have access to nutrients and are continuing to reproduce. The bacteria are competing for the nutrients. Some of the remaining bacteria are able to feed on the dead ones.

Finally the wastes from the bacteria buildup and the nutrients are few and far between. The bacteria starve and die on mass, the number of bacteria falls as they die. This is the death phase.  

Sensitivity

Chemotaxis - chemo is chemical and taxis is to move like to catch a taxi or the plane is taxing on the runway

Bacteria move towards and away from different things

This is because they can sense these things

Some bacteria will move away from light to prevent them from drying out, while photosynthetic bacteria will move towards it

Bacteria can sense nutrients due to diffusion gradients in their environment. Much like you can sense KFC when walking near by, and if your eyes were closed, you could probably figure out how to get to the store just using your chemosense - your nose

Chemosensing is the sensing of chemicals, including nutrients

For bacteria to chemosense, the some of the chemical compounds must either diffuse into the cell (the side of diffusion indicates the direction of the chemicals). Alternatively the compounds can touch a receptor, the side of the bacteria that has the activated receptor is the side that the chemicals must be on, so the bacteria will move either towards (nutrients) or away (toxins) from that chemical 

Growth

Often when we talk about bacterial growth, we are talking about the growth of bacterial colonies - so really we are talking about reproduction

However, reproduction can only happen when a bacterial cell has grown large enough that it can split - so the two things are related

The faster a bacterial cell can get atoms into its cell, the faster the cell can grow, so the sooner it will get large enough to divide, so the faster it will reproduce, and so the faster the bacterial population will increase, so the faster the bacterial colony will 'grow'.

Bacteria are made up of atoms

To get bigger they need more atoms!

To get more atoms they eat things. 

Bacteria eat by simply absorbing nutrients straight through their cell membrane

This might seem weird, but that is how all of our cells get their nutrients, our cells absorb them through their cell membrane. With the nutrients coming from the blood

Even in our intestine, the nutrients are absorbed through membrane of the cells of the villi in the small intestine

So, its a normal way for cells to get their nutrients, they absorb them

The movement of the nutrients to the cells is through concentration gradients. Usually once a nutrient is inside a cell

To digest food, the bacteria release digestive enzymes. These digestive enzymes move through to the substance to be digested and break it down, releasing small nutrients that dissolve in water and move down their concentration gradient. Away from where they are in high supply near the food, towards the bacteria that absorbs them through its membrane, thus making the nutrients 'disappear' and maintaining the concentration gradient

Ideal Bacterial Environment and their Growth

Growth of individual bacteria, or growth of the colony through the rate of reproduction (reproductive rate).

These are affected by the environment. 

Temperature is a good example of a abiotic environmental factor that can effect growth of both individual bacteria and growth of the colony (reproductive rate)

As the environment gets warmer, the molecules in liquids speed up. 

Water moves faster and the substances floating in the water speed up

Increase in temperature increases the kinetic energy of particles

The enzymes slam into the food source faster

The enzymes have more energy, the quickly bend the food source allowing the chemical reaction (usually hydrolysis) to occur splitting the food into smaller nutrients

Because water molecules are moving faster, these nutrients are carried in the water to the bacteria faster

They are absorbed into the bacteria faster and become part of the bacteria faster. 

Because the bacteria is absorbing atoms faster, it grows faster

As it grows faster, it gets to the size required for splitting faster. 

The bacteria thus splits into two. Thus reproduction via binary fission has occurred sooner.

So the number of bacteria doubles sooner.

Because molecules are moving faster, everything happens faster.

Nature and Denature

At temperatures closer to 50 degrees, the water molecules are moving so quickly that they shake the enzyme

The water molecules shake the enzyme so hard that its weaker hydrogen bonds break and the enzyme changes shape

This is 'denaturing'. A denatured enzyme no longer works.

Because the chemical reactions of life are conducted by enzymes, broken enzymes slows everything down.

As more enzymes are denatured, things slow down more, until the processes of life can no longer occur, and the bacteria die

This is one of the reasons that we cook our food. 

(The other reason we cook our food is to begin to hydrolyze cellulose, starch and proteins - in other words, to make the food softer and easier to eat)

pH can also denature proteins by breaking hydrogen bonds in the proteins. This is how our stomach acid kills bacteria

This food safety poster actually covers all the things that bacteria need to survive!

Food - Nutrition

Acidity -pH affects the bacteria

Time - time for the colonies to grow and get up to their exponential phases and their stationary phase

Temperature - the closer to human body temperature the faster the bacteria multiply

Oxygen - some bacteria breath oxygen

Moisture - bacteria need moisture in order to get dissolved nutrients into their cells from the environment

Respiration

Respiration is the process of breaking down large compounds, releasing chemical potential energy, and using this energy in the cell

This is related to breathing, in that for us we need oxygen to do this process

For use we combine a hydrocarbon (big compound) with oxygen, to make carbon dioxide (small compound) and water (small compound)

Whenever you combine small compounds together to make big compounds you need to put a lot of energy in

Think of building a brick wall by yourself. Putting each brick in takes energy. 

Whenever you break big compounds back down to small compounds you need to put in a small amount of energy, but you get a lot of energy out of the big compound

Think of using a sledgehammer to breakdown the wall. A small amount of energy to start it falling, a huge amount of energy out as it falls down. 

This relates to activation energy and energy graphs below

When compounds with lots of atoms are made from compounds that have few atoms, a lot of energy has to be put in. Some of that energy stays in the big compound. 

In other words, it takes lots of energy to build complex compounds from simple compounds and some of that energy is stored in the complex compound as chemical potential energy. 

When a big compound with lots of atoms is broken down into smaller compounds with fewer atoms, energy needs to be put in to start the reaction, but lots of energy is then released from the big compound

In other words, it takes some energy to start to deconstruct complex molecules into simple molecules, but that deconstruction releases lots of stored chemical potential energy

This is much like building a brick wall, and then pushing it over. 

Building by hand takes lots of energy. Pushing it over takes some energy. When it crashes down and brakes back into bricks we hear that energy being released.

Aerobic Respiration

All biological molecules contain Carbon. 

This Carbon enters living system as Carbon dioxide during photosynthesis and combines with Water to make a Carbohydrate (carbo = carbon, hydrate = water)

Enzymes in plants and in photosynthetic bacteria turn these carbohydrates into fats and into amino acids for proteins

These carbon based structures can be 'burnt'. This involves taking oxygen and combining it with the Carbon to remake Carbon dioxide. What is left over is water. 

Through this process, the large carbohydrate glucose (sugar) is broken into smaller carbon dioxide and water compounds. This releases chemical energy for the cell to use

This form of respiration is called 'Aerobic' respiration because it uses the air. 

This is like an Aeroplane. An aeroplane uses the air

More specifically though, Aerobic Respiration uses oxygen

Aerobic respiration breaks the carbohydrate glucose down to the smallest possible compounds, thus it releases the most energy from glucose. 

In other words, aerobic respiration releases the highest amount of energy possible

Anaerobic Respiration

Anaerobic Bacteria do not use oxygen (anaerobic - an no air)

So, no oxygen

The big carbohydrate compound (glucose) can still be broken down into smaller compounds to release stored chemical energy

But it can't be broken all the way down to Carbon dioxide, because there is no dioxide to bind the carbon onto

Breaking down carbohydrates without oxygen is also called Fermentation

Anaerobic Bacteria will do Lactic Acid Fermentation

The big 6 carbon carbohydrate, glucose, is broken down into two 3 carbon compounds called Lactic Acid. This releases only a small amount of energy

If this Acid is added to Milk the milk will become thick as it curdles in acid... Yoghurt

Anaerobic Respiration

C6H12O6 = C3H6O3 + C3H6O3  Chemical Energy released


Glucose = Lactic Acid + Lactic Acid  Chemical Energy released

Notice that the number of atoms and the number of each type of atom in Lactic Acid is exactly half that of Glucose

C6H12O6 = C3H6O3 + C3H6O3 

Excretion

Excretion of Carbon products

These are the 3 that are due to Respiration:

  1. Carbon dioxide (aerobic)


  1. Methane (anaerobic)

Excretion of Toxins

Imagine that you are in a tribe of humans trying to find food. 

Walking for years from place to place. Then you find a place that has food, enough for you and your tribe. 

What would you do to protect your find? To secure food for you and your tribe? You might make weapons and traps to keep others away.

For Bacteria, they can secrete Toxins. These are their weapons.

These weapons will be either excreted: exotoxin

Or released when they die: endotoxin

Bacteria excrete their exotoxin weapons for 2 reasons:

Competition - the use of Toxins in the War for food

The use of exotoxins to prevent bacterial to bacteria competition is used in agar art

Bacteria can be 'drawn' onto the agar plate. They then secrete toxins stopping the other bacteria from coming over to their 'space'. 

Sometimes one bacteria's toxin might be more effective than the others, it will then be able to kill of the other species and take the whole plate for its descendants

Hunting and killing - the use of Toxins to turn cells into food

This toxin is designed to turn cells into food

It is a pore forming toxin. 

The bacteria excretes this toxin. The bacteria is safe from its own toxin due to its slime layer

The toxin then arrives at a cell, and bores a tunnel into the cells membrane, a pore

This tunnel causes water to pour into the cell (osmosis) 

The cell can not stop the water from pouring in 

The cell swells, then bursts

The bacteria moves over and digests the remnants of the burst cell. 

Flesh eating bacteria secrete a pore forming toxin, as well as others that cause blood cells to burst and all the cells in the flesh to die. This all becomes food for the bacteria, which then eat, grow, reproduce, repeat.

Bacterial Toxins in Human Disease

Botulism toxin is a exotoxin that is one of the deadliest

Luckily, it is easily destroyed by cooking

As are the toxins from Salmonella and Campylobacter

This is why cooking your food thoroughly is so important.

However, not all toxins can be destroyed through cooking.

This is why once food is 'off' cooking it will not make it safe. Despite killing the bacteria and destroying many of the toxins, there will still be many toxins that will retain their toxicity. 


Exposure to very high levels of bacterial toxins can cause 'toxic shock' which is when the immune system goes nuclear on the toxins. The chaos that follows causes multi-organ failure and death die

Nutrition

The best clip of how the life of decay feeds back into food chains

Extracellular Digestion

Bacteria eat by releasing releasing digestive enzymes into their environment

Basically, this is like vomiting onto your food to digest it, then sipping up the digested mess

These digestive enzymes, like Lactase, diffuse away from the bacteria and arrive at large nutrients like Lactose

They then cut up the large nutrients into small soluble molecules like glucose

These nutrients then diffuse towards the bacteria and either diffuse across the cell membrane or are transported across the membrane using channels. 

Temperature affects the rate of diffusion. Cold is slow and warm is fast.

These channels either operate through passive diffusion and just facilitate the diffusion (facilitated transport) or they use some ATP to actively facilitate the movement of nutrients (active transport)

The Internal Assessment reminder