Author Topic: Edexcel BIOLOGY Doubts!!!!  (Read 130941 times)

Offline hissyfit

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Re: Edexcel BIOLOGY Doubts!!!!
« Reply #315 on: February 24, 2011, 03:09:53 pm »
Can anybody help me with SAQ12(a) ,I can t find the mark scheme...
It s the qs for Practical 4
thanks
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Amelia

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Re: Edexcel BIOLOGY Doubts!!!!
« Reply #316 on: February 24, 2011, 07:12:58 pm »
SAQ 12 The graph below shows the results of an investigation into the effect of substrate concentration on the initial rate of enzyme controlled reaction.

a) Suggest two conditions apart from temperature that should be kept constant in this investigation.

pH and substrate concentration.

Offline hissyfit

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Re: Edexcel BIOLOGY Doubts!!!!
« Reply #317 on: February 24, 2011, 09:22:32 pm »
thanks + rep,to my own surprise I was thinking the same as you (I m not the best  bio student there is)
 how would you keep pH constant?
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Offline Deadly_king

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Re: Edexcel BIOLOGY Doubts!!!!
« Reply #318 on: February 25, 2011, 04:01:39 am »
thanks + rep,to my own surprise I was thinking the same as you (I m not the best  bio student there is)
 how would you keep pH constant?

pH is kept constant by using a buffer.

In biology, you don't really need to know what a buffer is made up of. However you'll study them in Chemistry. ;)

Here you are :)


Offline hissyfit

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Re: Edexcel BIOLOGY Doubts!!!!
« Reply #319 on: February 25, 2011, 08:27:37 am »
ahhhh,I see a little bit complicated for me but I think I get the main function...

Thanks :D
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Offline hissyfit

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Re: Edexcel BIOLOGY Doubts!!!!
« Reply #320 on: March 10, 2011, 02:04:23 pm »
hi

I made different concentrations of catalase (from potato) and was wondering how I could accurately say that the enzyme concentrations will be different in different areas of the test tubes as some particles will sink to the bottom.I m not sure if its the heavy particles ...
thanks
+ rep
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Offline Blizz_rb93

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Re: Edexcel BIOLOGY Doubts!!!!
« Reply #321 on: March 11, 2011, 06:29:56 pm »
Can somebody let me know what we need to know about the structures of proteins;
Primary Proteins, Secondary Proteins, Tertiary Proteins & Quaternary proteins
Do they have functions that we need to know?
& Can someone let me know what are the shapes of each required to know?

Thank you.

Offline Deadly_king

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Re: Edexcel BIOLOGY Doubts!!!!
« Reply #322 on: March 12, 2011, 06:09:13 am »
hi

I made different concentrations of catalase (from potato) and was wondering how I could accurately say that the enzyme concentrations will be different in different areas of the test tubes as some particles will sink to the bottom.I m not sure if its the heavy particles ...
thanks
+ rep


If it is for class purposes, then you need to stir the mixture for about one whole minute. Then you can state its concentration exactly and accurately, ;)

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Re: Edexcel BIOLOGY Doubts!!!!
« Reply #323 on: March 12, 2011, 06:20:09 am »
Can somebody let me know what we need to know about the structures of proteins;
Primary Proteins, Secondary Proteins, Tertiary Proteins & Quaternary proteins
Do they have functions that we need to know?
& Can someone let me know what are the shapes of each required to know?

Thank you.

Protein Structure
Polypeptides are just a string of amino acids, but they fold up to form the complex and well-defined three-dimensional structure of working proteins. To help to understand protein structure, it is broken down into four levels:

1.    Primary Structure

This is just the sequence of amino acids in the polypeptide chain, so is not really a structure at all. However, the primary structure does determine the rest of the protein structure. Finding the primary structure of a protein is called protein sequencing, and the first protein to be sequenced was the protein hormone insulin, by the Cambridge biochemist Fredrick Sanger, for which work he got the Nobel prize in 1958.

2.    Secondary Structure



This is the most basic level of protein folding, and consists of a few basic motifs that are found in all proteins. The secondary structure is held together by hydrogen bonds between the carboxyl groups and the amino groups in the polypeptide backbone. The two most common secondary structure motifs are the a-helix and the b-sheet.

The a-helix.
The polypeptide chain is wound round to form a helix. It is held together by hydrogen bonds running parallel with the long helical axis. There are so many hydrogen bonds that this is a very stable and strong structure. Do not confuse the a-helix of proteins with the famous double helix of DNA. Helices are common structures throughout biology.

The b-sheet.
The polypeptide chain zig-zags back and forward forming a sheet of antiparallel strands. Once again it is held together by hydrogen bonds.

The a-helix and the b-sheet were discovered by Linus Pauling, for which work he got the Nobel prize in 1954. There are a number of other secondary structure motifs such as the b-bend, the triple helix (only found in collagen), and the random coil.

3.    Tertiary Structure

This is the compact globular structure formed by the folding up of a whole polypeptide chain. Every protein has a unique tertiary structure, which is responsible for its properties and function. For example the shape of the active site in an enzyme is due to its tertiary structure. The tertiary structure is held together by bonds between the R groups of the amino acids in the protein, and so depends on what the sequence of amino acids is. There are three kinds of bonds involved:

1. hydrogen bonds, which are weak.
2. ionic bonds between R-groups with positive or negative charges, which are quite strong.
3. sulphur bridges - covalent S-S bonds between two cysteine amino acids, which are strong.

So the secondary structure is due to backbone interactions and is thus largely independent of primary sequence, while tertiary structure is due to side chain interactions and thus depends on the amino acid sequence.

4.    Quaternary Structure

This structure is found in proteins containing more than one polypeptide chain, and simply means how the different polypeptide chains are arranged together. The individual polypeptide chains are usually globular, but can arrange themselves into a variety of quaternary shapes. e.g.:

Haemoglobin, the oxygen-carrying protein in red blood cells, consists of four globular subunits arranged in a tetrahedral (pyramid) structure. Each subunit contains one iron atom and can bind one molecule of oxygen.
   
Immunoglobulins, the proteins that make antibodies, comprise four polypeptide chains arranged in a Y-shape. The chains are held together by sulphur bridges. This shape allows antibodies to link antigens together, causing them to clump.
   
Actin, one of the proteins found in muscles, consists of many globular subunits arranged in a double helix to form long filaments.
   
Tubulin is a globular protein that polymerises to form hollow tubes called microtubules. These form part of the cytoskeleton, and make cilia and flagella move.
   

These four structures are not real stages in the formation of a protein, but are simply a convenient classification that scientists invented to help them to understand proteins. In fact proteins fold into all these structures at the same time, as they are synthesised.

The final three-dimensional shape of a protein can be classified as globular or fibrous.

globular structure

   

fibrous (or filamentous) structure


The vast majority of proteins are globular, including enzymes, membrane proteins, receptors, storage proteins, etc. Fibrous proteins look like ropes and tend to have structural roles such as collagen (bone), keratin (hair), tubulin (cytoskeleton) and actin (muscle). They are usually composed of many polypeptide chains. A few proteins have both structures: the muscle protein myosin has a long fibrous tail and a globular head, which acts as an enzyme.

This diagram below shows a molecule of the enzyme dihydrofolate reductase, which comprises a single polypeptide chain. It has been drawn to highlight the different secondary structures.


This diagram below shows part of a molecule of collagen, which is found in bone and cartilage. It has a unique, very strong triple-helix structure.
]

I think that is all you need to know ;)

Offline Blizz_rb93

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Re: Edexcel BIOLOGY Doubts!!!!
« Reply #324 on: March 12, 2011, 09:21:52 am »
Thank you! :)

Offline Deadly_king

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Re: Edexcel BIOLOGY Doubts!!!!
« Reply #325 on: March 12, 2011, 09:36:59 am »

Offline Hissa

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Re: Edexcel BIOLOGY Doubts!!!!
« Reply #326 on: March 18, 2011, 08:33:41 am »
What are the disadvantages of limitations of using a respirometer?

Offline SoONa

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Re: Edexcel BIOLOGY Doubts!!!!
« Reply #327 on: March 21, 2011, 09:50:54 am »
hey can someone please help me out with the fluid mosaic membrance structure .. what do i need to know??
thanks in advance

Amelia

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Re: Edexcel BIOLOGY Doubts!!!!
« Reply #328 on: March 21, 2011, 03:22:48 pm »
hey can someone please help me out with the fluid mosaic membrance structure .. what do i need to know??
thanks in advance

The Plasma membrane is a bi-layer of phospholipids.Each phospholipid molecule has a head that is attracted to water (hydrophilic: hydro = water; philic = loving) and a tail that repels water (hydrophobic: hydro = water; phobic = fearing). Both layers of the plasma membrane have the hydrophilic heads pointing toward the outside; the hydrophobic tails form the inside of the bilayer.
Because cells reside in a watery solution (extracellular fluid), and they contain a watery solution inside of them (cytoplasm), the plasma membrane forms a circle around each cell so that the water-loving heads are in contact with the fluid, and the water-fearing tails are protected on the inside.
Proteins and substances such as cholesterol become embedded in the bilayer, giving the membrane the look of a mosaic. Because the plasma membrane has the consistency of vegetable oil at body temperature, the proteins and other substances are able to move across it. That’s why the plasma membrane is described using the fluid-mosaic model.

The molecules that are embedded in the plasma membrane also serve a purpose. For eg:-

-The cholesterol that is stuck in there makes the membrane more stable and prevents it from solidifying when your body temperature is low. (It keeps you from literally freezing when you’re “freezing.”)

-Most proteins float about in the phospholipid bilayer forming a fluid mosaic pattern. The proteins stay in the membrane because they have regios of hydrophobic aminoacids which interact with the fatty acid tails and excludes water. The rest of the protein faces into the cell or out in the external environment, both of which are aqueous.

-Some proteins and lipids have short Carbohydrate chains like antennae forming glycoproteins and glycolipids, respectively. These carbohydrates are specific to every person, and they supply characteristics such as your blood type.


~ The Phospholipids are fluid and can move about by diffusion in their own layers.
~The mor unsaturated the tails of the phospholipid, the more fluid the membrane is.
~The membrane is about 7nm thick.  ::)
 
« Last Edit: March 21, 2011, 03:27:10 pm by Amelia »

Offline Hermione Granger

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Re: Edexcel BIOLOGY Doubts!!!!
« Reply #329 on: March 23, 2011, 07:10:22 pm »
hey can someone please help me out with the fluid mosaic membrance structure .. what do i need to know??
thanks in advance
amelia's given a good descriptn....and il add:
the glycoproteins that are present on the cell surface membrane play a vital role in cell recognition...it helps to differentiate between bodys own cells and foreign cells...helps in immunity(but u got to know that part in A2..for AS jus knw the recognition part)!!
Also go through the basics of enzyme-working, because the working of the membrane is greatly determined by the diff in pH,temp n so on... that usually affect the workin of an enzyme...because naturally...plasma membrane has the presence of proteins n enzyme are proteins 2...(duh!.=D)..so, any changes to the pH or extreme temp above optimum, will lead to the denaturation of these proteins,and so affect the permeability of the cell.
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