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March 29, 2024, 09:08:33 pm

Author Topic: VCE Biology Question Thread  (Read 3571583 times)  Share 

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MM1

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Re: VCE Biology Question Thread
« Reply #240 on: January 16, 2014, 05:38:47 pm »
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Free ribosomes are the site of protein synthesis, for proteins that carry out their biological function within the cells they are produced. Ribosomes studded on the endoplasmic reticulum, which forms the rough endoplasmic reticulum organelle, synthesise proteins that carry out their biological function outside the cell in which they are produced.

The endoplasmic reticulum is an organelle made up of a network of membranous sacs, transporting substances within the cell and also partially modify the substances transported within the cell. It is the golgi apparatus that packages synthesised materials into vesicles that bud off the golgi body, and transport the synthesised materials out of the cell by exocytosis.

Thanks! Can the smooth and rough E.R interact; does it always have to follow the sequential steps of E.R > Golgi complex > vesicle?

Yacoubb

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Re: VCE Biology Question Thread
« Reply #241 on: January 16, 2014, 05:45:02 pm »
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Thanks! Can the smooth and rough E.R interact; does it always have to follow the sequential steps of E.R > Golgi complex > vesicle?

The smooth endoplasmic reticulum synthesises lipids and transports them within cells, whereas the rough endoplasmic reticulum synthesises proteins and transports them within cells. So no, they don't react.

Yes, the step is rough endoplasmic reticulum --> golgi complex --> vesicle!

alchemy

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Re: VCE Biology Question Thread
« Reply #242 on: January 16, 2014, 07:36:22 pm »
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In reference to pages 29 & 185 of Cambridge checkpoints 2013:

Q: In fibrous proteins, the polypeptide chains are arranged in parallel to form long fibres or sheets. In globular proteins, the polypeptide chains are folded into compact spherical or globular shapes. Describe a distinctive property of a fibrous protein and explain how this property is due to the arrangement of its polypeptides?

The answer says that one of the properties is its elasticity. But I'm confused because silk is an example of a fibrous protein and I know that silk does NOT stretch due its tightly constructed beta pleats secondary structure.

Could someone please explain this to me??

Thanks!

Notice that the actual answer addresses two points, which I have summarized below:

1) The parallel arrangement of polypeptides means that they form long fibers or sheets. This refers to the beta pleated sheets as a secondary structure. Silk is well known for this property.
2) Some, but not all, fibrous proteins can be stretched and then return to their original shape. This refers to a protein's alpha helices.

You've only quoted one of them in your question.
You may have reached the correct conclusion if you payed attention to when the question asked "explain how this property as due to the arrangement of polypeptides". Fibrous proteins can have either an alpha helix or a beta pleated sheet. Recall that alpha helices can be twisted or stretched and return to their original shape. Beta pleated sheets, on the other hand, do the opposite. They are rigid and cannot be stretched. I would negate the comparison to a globular protein. That's not exactly what the question asks for. Anyway, hopefully I answered your question ( :

grannysmith

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Re: VCE Biology Question Thread
« Reply #243 on: January 16, 2014, 07:53:28 pm »
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In reference to pages 29 & 185 of Cambridge checkpoints 2013:

Q: In fibrous proteins, the polypeptide chains are arranged in parallel to form long fibres or sheets. In globular proteins, the polypeptide chains are folded into compact spherical or globular shapes. Describe a distinctive property of a fibrous protein and explain how this property is due to the arrangement of its polypeptides?

The answer says that one of the properties is its elasticity. But I'm confused because silk is an example of a fibrous protein and I know that silk does NOT stretch due its tightly constructed beta pleats secondary structure.

Could someone please explain this to me??

Thanks!

Elasticity is only one property, and silk is only one form of fibrous protein.
The reason silk is relatively rigid is due to its beta pleated sheets, so you're correct. But this doesn't mean it's elastic. Rather, it isn't.

Basically, the arrangement (secondary structure) of a polypeptide determines its property.

millie96

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Re: VCE Biology Question Thread
« Reply #244 on: January 16, 2014, 09:47:53 pm »
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In the study design it says 'polysaccharides and their glucose monomers' --> are the glucose monomers like starch,cellulose etc?

datfatcat

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Re: VCE Biology Question Thread
« Reply #245 on: January 16, 2014, 09:52:38 pm »
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In the study design it says 'polysaccharides and their glucose monomers' --> are the glucose monomers like starch,cellulose etc?
Glucose, fructose and galactose are examples of monomers. Starch and cellulose are polysaccharide. (Starch consists of a large number of glucose units joined by glycosidic bonds)
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vox nihili

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Re: VCE Biology Question Thread
« Reply #246 on: January 16, 2014, 10:27:51 pm »
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Basically, the arrangement (secondary structure) of a polypeptide determines its property.

I'm not sure this is correct. Each level of structure plays a part in the role of a protein.

The primary structure determines the sequence of amino acid residues in the polypeptide, which in turn determines the basic folding patterns of the secondary structure, which then in turn determine the overall folding pattern of the tertiary structure, which can then influence the ability of a polypeptide to associate with other polypeptides in a quaternary structure.
It would be folly to say that the secondary structure is the most important. The tertiary/quaternary structure is what allows the protein to carry out its functions. Any changes to that are what researches are normally concerned with. Many of those changes involve a change in the primary structure (base sequence of the DNA essentially), which alter everything thereafter.
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grannysmith

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Re: VCE Biology Question Thread
« Reply #247 on: January 16, 2014, 10:34:55 pm »
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I'm not sure this is correct. Each level of structure plays a part in the role of a protein.

The primary structure determines the sequence of amino acid residues in the polypeptide, which in turn determines the basic folding patterns of the secondary structure, which then in turn determine the overall folding pattern of the tertiary structure, which can then influence the ability of a polypeptide to associate with other polypeptides in a quaternary structure.
It would be folly to say that the secondary structure is the most important. The tertiary/quaternary structure is what allows the protein to carry out its functions. Any changes to that are what researches are normally concerned with. Many of those changes involve a change in the primary structure (base sequence of the DNA essentially), which alter everything thereafter.

My bad. I was referring to the way the quantity of alpha helices/beta pleats generally determines whether the fibrous protein is more elastic or rigid. But I may be wrong :/ Sorry for that

vox nihili

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Re: VCE Biology Question Thread
« Reply #248 on: January 16, 2014, 10:54:14 pm »
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My bad. I was referring to the way the quantity of alpha helices/beta pleats generally determines whether the fibrous protein is more elastic or rigid. But I may be wrong :/ Sorry for that

In that case, sure that's a reasonable assumption to make, it's just not one that you want to generalise, because I think the course really tries to stress the interrelationship between the various levels of protein structure. It's an important consideration to make, so I wanted to clear that up.

Don't be sorry! That's exactly what everyone's here for, for that back and forth. Plus, only the completely stupid are always right :)
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vella97

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Re: VCE Biology Question Thread
« Reply #249 on: January 16, 2014, 11:02:57 pm »
+1
Notice that the actual answer addresses two points, which I have summarized below:

1) The parallel arrangement of polypeptides means that they form long fibers or sheets. This refers to the beta pleated sheets as a secondary structure. Silk is well known for this property.
2) Some, but not all, fibrous proteins can be stretched and then return to their original shape. This refers to a protein's alpha helices.

You've only quoted one of them in your question.
You may have reached the correct conclusion if you payed attention to when the question asked "explain how this property as due to the arrangement of polypeptides". Fibrous proteins can have either an alpha helix or a beta pleated sheet. Recall that alpha helices can be twisted or stretched and return to their original shape. Beta pleated sheets, on the other hand, do the opposite. They are rigid and cannot be stretched. I would negate the comparison to a globular protein. That's not exactly what the question asks for. Anyway, hopefully I answered your question ( :

I've only quoted one in the question because that is how the question appeared in the Checkpoints, which confused me because I knew that beta pleats structures could not stretch. Should it have been made clearer in the question or is this supposed to be assumed knowledge? And if it's supposed to be assumed knowledge, then what was the point of stating the first type of structure of a fibrous protein in the first place?

Thanks for your help!

alchemy

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Re: VCE Biology Question Thread
« Reply #250 on: January 17, 2014, 08:26:51 am »
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I've only quoted one in the question because that is how the question appeared in the Checkpoints, which confused me because I knew that beta pleats structures could not stretch. Should it have been made clearer in the question or is this supposed to be assumed knowledge? And if it's supposed to be assumed knowledge, then what was the point of stating the first type of structure of a fibrous protein in the first place?

Thanks for your help!

Like I said before, the question asks for you to refer to the "arrangement of polypeptides" in your answer. This, in other words, means something to do with the proteins structure (Primary, Secondary, Tertiary or Quaternary). We only have to really consider the secondary structure as the question states the type of structure as a fibrous protein, as you correctly recalled. So it's not exactly "assumed knowledge" in this case, but rather knowing how to interpret the question. 

MM1

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Re: VCE Biology Question Thread
« Reply #251 on: January 17, 2014, 02:53:20 pm »
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How is non-competitive inhibition reversed?

MM1

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Re: VCE Biology Question Thread
« Reply #252 on: January 17, 2014, 05:45:17 pm »
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Can someone please provide a concise definition of 'denaturation'? One that possibly encompasses the following points:
  • It's irreversible
  • Loss of 3-dimensional shape.
  • Results from an altercation of bonds.
  • Rendering the protein non-functional
  • Is caused by a variety of factors

Cheers!

alondouek

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Re: VCE Biology Question Thread
« Reply #253 on: January 17, 2014, 06:03:53 pm »
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Can someone please provide a concise definition of 'denaturation'? One that possibly encompasses the following points:
  • It's irreversible
  • Loss of 3-dimensional shape.
  • Results from an altercation of bonds.
  • Rendering the protein non-functional
  • Is caused by a variety of factors

Cheers!

You're pretty much already done! haha

"Denaturation is the irreversible loss of 3-dimensional protein shape due to the alteration of intra-molecular bonds. This is due to environmental factors such as heat or pH, and renders the denatured protein non-functional".

:)
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MM1

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Re: VCE Biology Question Thread
« Reply #254 on: January 17, 2014, 06:22:55 pm »
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You're pretty much already done! haha

"Denaturation is the irreversible loss of 3-dimensional protein shape due to the alteration of intra-molecular bonds. This is due to environmental factors such as heat or pH, and renders the denatured protein non-functional".

:)

Thanks alondouek for that condensed definition :)