1st course, Bacteria
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Name and describe the micro-organism used in yoghurt making
Describe the steps to produce yoghurt and explain the role of bacteria in this process
Link the Life processes of the bacteria to the production of yoghurt
Describe the most important bacterial life processes in the production of yoghurt
Explain how these life processes help to produce yoghurt
Link the physical characteristics of yoghurt to these life processes
Discuss the effect of different environmental factors (temperature and pH) on the production of yoghurt
Explain how the environmental factors affect the relevant bacterial life processes
Explain how the affected life processes impact the production of yoghurt
Explain how the produced yoghurt is preserved through elimination of other unwanted micro-organisms
Discuss the impacts of this knowledge of micro-organisms and food production on your everyday life
Structure of a Bacteria
Structure of a Bacteria
If we look at the structure of bacteria we will find:
Cytoplasm - The chemical reactions of life need to happen in a fluid filled environment, to allow for the chemicals to move
The cytoplasm is mostly water. In this water is all of the chemicals of life - dissolved oxygen, carbon dioxide, sugars, lipids and proteins along with nucleic acids
DNA - this contains the genetic instructions to make all of the proteins and enzymes of the cell
Plasmid - smaller circular bits of DNA that code for making proteins and enzymes, these can be shared between bacteria
Ribosomes - these are enzymes that make proteins
Proteins are either structural or they are enzymes. Enzymes are proteins that do stuff.
Cell membrane - this is made from lipid. This lets nutrients, wastes and oxygen diffuse into and out of the cell
Cell Wall - this is strong and provides structure for the cell
Capsule - even stronger
Slime layer - this helps to keep water inside the cell and prevents it from drying out. It can also hid the cell from animal immune systems
Pili - these are like tiny fingers that help to hold the bacteria in place so that it can feed
Occasionally one of the pili might become a sex pilus so that two bacteria can exchange genetic material
Flagellum - by moving the tail like flagellum, the bacteria can move and swim
Life Processes
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
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
Reproduction
Binary Fission
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
Bacterial Growth Curves
Lag Phase - The bacteria are releasing digestive enzymes to make nutrients available, absorbing the nutrients and growing in individual size
Exponential Phase - The bacteria are multiplying, the colony is growing. There is plenty of nutrients to provide the atoms for this growth and reproduction
Stationary Phase - There is not enough nutrients to go around. Some bacteria are able to get enough nutrients to stay alive and respire but not divide. There are some bacteria that are able to get an abundance of nutrients and can grow and reproduce. There are some bacteria that are not able to get enough nutrients to sustain respiration, so they die
Death phase - There is not enough nutrients so the bacteria starve and die off.
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
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
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
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
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 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
Excretion of Carbon products
Excretion of Carbon products
These are the 3 that are due to Respiration:
- Carbon dioxide (aerobic)
If the bacteria is a obligate aerobe or a facultative anaerobe in an oxygen rich environment, then it will conduct aerobic respiration.
Aerobic respiration: Glucose + Oxygen = Carbon dioxide + Water (+ lots of energy)
The Carbon Dioxide diffuses out of the bacteria and re enters the air
- Lactic Acid (anaerobic)
If the bacteria is a obligate anaerobe or a facultative anaerobe in a hypoxic (low O2) or anoxic (no O2) environment then it will conduct anaerobic respiration
Lactic acid Anaerobic respiration: Glucose = Lactic Acid + Lactic Acid (+ little bit of energy)
- Methane (anaerobic)
If the bacteria is a methanogenic bacteria then it will be an obligate anaerobe that produces methane
Methanogenic Anaerobic respiration: Glucose = Methane + Carbon Dioxide
Excretion of Toxins
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 (War)
To keep the food for only their species
once the bacteria have found a new food supply, the release of toxins will stop other species from becoming established
These toxins will Kill other bacterial species
Hunting and Killing
To turn other cells into food
some of the toxins are designed to kill other cells so that they can become food
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
Nutrition
The best clip of how the life of decay feeds back into food chains
Extracellular Digestion
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
Name and describe the micro-organism used in yoghurt making
Describe the steps to produce yoghurt and explain the role of bacteria in this process
Link the Life processes of the bacteria to the production of yoghurt
Describe the most important bacterial life processes in the production of yoghurt
Explain how these life processes help to produce yoghurt
Link the physical characteristics of yoghurt to these life processes
Discuss the effect of different environmental factors (temperature and pH) on the production of yoghurt
Explain how the environmental factors affect the relevant bacterial life processes
Explain how the affected life processes impact the production of yoghurt
Explain how the produced yoghurt is preserved through elimination of other unwanted micro-organisms
Discuss the impacts of this knowledge of micro-organisms and food production on your everyday life
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