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Cells and Cell Processes

WJEC Unit 2 Chapter 1
by

Alex Van Dijk

on 10 October 2012

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Transcript of Cells and Cell Processes

Cells and Cell Processes What are cells? Microscopes Animal and Plant Cells Cells are the basic unit of all living things. All living organisms are made up out of 1 or more cells (many trillions in our case). Robert Hooke was the person to describe cells in cork in 1665. Schwann and Schleiden in the 1830s were the first to propose what is now known as cell theory, which states that all living things consist of cells. Cell theory nowadays consists of 6 statements: 1. All living organisms consist of cells. They maybe be unicellular or multicellular 2. The cell is the basic unit of life 3. Cells are formed from pre-existing cells during cell division 4. Energy flow (the production of biological molecules and energy from these molecules) occurs within cells. 5. Hereditary information (DNA) is passed from cell to cell during cell division (as we saw in the genetics topic last year). 6. All cells have the same basic chemical composition Light Microscope Transmission Electron Microscope Scanning Electron Microscope Confocal Laser Scanning Microscope Animal and plant cells share certain components, but not all of them are the same. As you can see cells are made up out of a number of different components. We will looked at the shared components first. The cell membrane forms the barrier between the cell and the outside. It controls what can go in and out of the cell The cytoplasm is the liquid that fills the cell, and in the case of animal cells, gives it its shape. Substances can move throughout the cytoplasm and many reactions take place here. The cell nucleus is surrounded by a membrane. It separates the DNA (which is packaged in chromosomes) from the cytoplasm to protect it. Mitochondria are organelles ("little organs") inside cells that carry out aerobic respiration. This is the breakdown of glucose in presence of oxygen releasing energy. Ribosomes are responsible for turning messages from the nucleus into amino acid sequences for proteins. Plants have some components that animal cells do not. The cell wall gives shape to the plant cell and is made of cellulose. Chloroplasts are organelles surrounded by a membrane where photosynthesis takes place. The vacuole contains cell sap. This is a mixture of water, sugars and other substances. Plants cells use it for storage. Specialised cells Multicellular organisms have cells that adapted for specific tasks.
These cells are known as specialised cells. When specialised cells divide they make more of the same type of cell (so a muscle cell makes two muscle cells rather than say a muscle cell and a liver cell). Cells that can turn into other cell types are known as stem cells.
An early embryo is made up out embryonic stem cells which can turn into any type of tissue.
Bone marrow contains cells that can turn into the various blood cell types. Look up a minimum of two specialised cell types (1 from animals and 1 from plants). Find an image and label the cell's characteristics and how it is different from the generic cell that we saw earlier. A Multicellular Organism Muscle cells Liver cell Cone cells in the eye Adipose (fat) cells Cells of microorganisms Bacteria divide by splitting in two.
We call this binary fission.
The daughter cells are identical to the parent cell.
When the offspring are identical to the parent we call this asexual reproduction.
What are some of the advantages and disadvantages of reproducing asexually? Some fungi are also single-celled organisms.
One of these is yeast. The yeast uses the carbohydrates in the bread as a source of energy.
The products of respiration include CO2, which gets trapped in the gluten of the bread, causing it to rise. When yeast does not have enough oxygen to carry out respiration it will digest glucose anaerobically. This process is known as fermentation. One of the products of anaerobic fermentation in yeast is ethanol. How is this different to the algal and bacterial cells? Yeast cells reproduce asexually by budding. What do we use yeast for, and how does it work? Viruses Viruses are often classed as non-living disease-causing agents.
Whilst they can replicate inside of a host cell they don't show many of the signs of life outside of a host. Viruses do not look like cells. They consist of a protein capsid that surrounds its genetic material (which can be DNA or RNA). There is no cytoplasm and most viruses do not have membrane surrounding them. There are a number of reasons why they are often not classed as living organisms.
They can be crystallised
They can only reproduce inside a host cell
They have no metabolism of their own. They rely on the host. You could argue that they are alive because:
They have genes that code for proteins
They respond to natural selection
They can reproduce and infect more cells.

Some scientists argue that viruses should therefore be classified as being "on the edge of life". DNA, Proteins and Enzymes Cells contain a number of biologically active molecules. These include proteins, specialised proteins known as enzymes and nucleic acids such as DNA. Proteins Proteins are typically very large molecules. They are polymers made up out of a very long chain of amino acids. The structure of a protein depends on the sequence of amino acids in the protein.
As there are 20 different amino acids and most proteins are more than a hundred amino acids long there are many possible structures. For a protein with 100 amino acids there are a total of 20 possible combinations. This is a number containing 130 digits! 100 Proteins can have multiple different functions:
structural (for example the collagen in your skin)
hormones (such as insulin)
enzymes The function of a protein depends on its 3D structure. If this structure changes then the protein might not be able to carry out its function. Enzymes Enzymes are proteins that act as catalysts within the cell. A catalyst is a substance that speeds up a chemical reaction by lowering the energy required for the reaction to occur, but is not used up in the process. You might for example say that the enzyme amylase in your saliva catalyses the breakdown of starch into maltose.
Whereas starch might naturally breakdown into smaller pieces, amylase speeds this reaction up and makes sure that only maltose is produced. Enzymes work because they have a very specific shape. This includes an active site where the molecule(s) it acts on (the substrate(s)) will bind. This is known as the lock-and-key model If the active site changes shape then the substrate can no longer fit into it, and the enzyme can no longer catalyse the reaction. Most enzymes show an activity curve in response to temperature changes that looks something like this. As the temperature goes up, the rate of of enzyme activity goes up.
As the temperature exceeds the optimum temperature (which would be 37C in our bodies) the bonds that hold the enzyme in shape are starting to stretch and break.
The enzyme changes shape and the active site can no longer catalyse the reaction.
This is known as denaturation. A graph showing enzyme activity at different pH values will also show denaturation occurring as the pH moves from the optimum value, as the change in pH results in some of the bonds breaking that give the enzyme shape. You can also plot graphs of substrate concentration against enzyme activity and enzyme concentration against enzyme activity. Both will look like this: In the case of the substrate concentration the limiting factor will become the number of active sites that are available. If all active sites are occupied 100% of the time the rate cannot increase. As the concentration goes up the rate goes up until it levels off as something else becomes the limiting factor. For the enzyme concentration the limiting factor becomes the availability of substrate that is able to get into the active site. Some of the enzymes will end up not catalysing any reactions for periods of time. Uses of Enzymes Enzymes are used in a number of industrial processes. These include pre-digesting food for babies, sewage treatment and the main one you need to be aware of: washing powders. Many stains are of biological nature (mainly food, but also grass stains etc.) and therefore there are enzymes that can break them down. Fat stains are normally hard to treat but lipases break them down into glycerol and fatty acids which are both soluble.
Using lipases in washing powder therefore allows for easier removal of grease stains. Biological washing powders work at lower temperatures than non-biological washing powders, which reduces the temperature you need to wash your clothes at. What would happen if you used biological washing powder in a 60C wash?
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