Topic 2 biochem student notes 2015

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http://bioknowledgy.weebly.com/ (Chris Paine)

Understandings, Applications and Skills (This is what you maybe assessed on) Statement Guidance

2.1.U.1 Molecular biology explains living processes in terms of the chemical substances involved.

2.1.U.2 Carbon atoms can form four covalent bonds allowing a diversity of stable compounds to exist.

2.1.U.3 Life is based on carbon compounds including carbohydrates, lipids, proteins and nucleic acids.

Sugars include monosaccharides and disaccharides. Only one saturated fat is expected and its specific name is not necessary. The variable radical of amino acids can be shown as R. The structure of individual R-groups does not need to be memorized.

2.1.U.4 Metabolism is the web of all the enzyme-catalysed reactions in a cell or organism.

2.1.U.5 Anabolism is the synthesis of complex molecules from simpler molecules including the formation of macromolecules from monomers by condensation reactions.

2.1.U.6 Catabolism is the breakdown of complex molecules into simpler molecules including the hydrolysis of macromolecules into monomers.

2.1.A.1 Urea as an example of a compound that is produced by living organisms but can also be artificially synthesized.

2.1.S.1 Drawing molecular diagrams of glucose, ribose, a saturated fatty acid and a generalized amino acid.

Only the ring forms of D-ribose, alpha–D-glucose and beta-D-glucose are expected in drawings.

2.1.S.2 Identification of biochemicals such as sugars, lipids or amino acids from molecular diagrams.

Students should be able to recognize from molecular diagrams that triglycerides, phospholipids and steroids are lipids. Drawings of steroids are not expected. Proteins or parts of polypeptides should be recognized from molecular diagrams showing amino acids linked by peptide bonds.

http://bioknowledgy.weebly.com/

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2.1.U1 Molecular biology explains living processes in terms of the chemical substances involved. 2.1.U4 Metabolism is the web of all the enzyme-catalysed reactions in a cell or organism. 1. The structure of DNA was discovered in 1953, since then molecular Biology has transformed our

understanding of living processes. a. Outline the relationship between genes (DNA) and polypeptides. (page 24)

b. Outline what the term metabolic pathway means. (page 17)

c. Referring to the term metabolic pathway describe what the term metabolism means to a molecular biologist. (page 101)

d. Describe the reductionist approach that a molecular biologist uses discover the working of a metabolic pathway. (page 20)

e. Explain why ultimately the reductionist approach used by molecular biologists might be a limited one. (page 20)

2.1.U2 Carbon atoms can form four covalent bonds allowing a diversity of stable compounds to exist. 2. Despite only being the 15th most abundant element on the planet carbon forms the backbone of every

single organic molecule. a. What type of bonds can carbon molecules form? And how does the strength of these bonds

compare with other types of bond? (page 17)

b. Explain why Carbon can form four bonds with up to four different atoms, and explain why. (slide 23)


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2.1 U.3 Life is based on carbon compounds including carbohydrates, lipids, proteins and nucleic acids. 3. Compare the key feature of the different groups of organic molecules by completing the table below.

Key features Examples

Carbohydrates (page 24)

Lipids (page 25)

Proteins (page 26)

nucleic acids (page 27)


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2.1.S1 Drawing molecular diagrams of glucose, ribose, a saturated fatty acid and a generalized amino acid.

4. Draw the simplified (ring) structures of glucose and ribose. Number the carbon atoms correctly. Which sugar is a pentose? Which is a hexose? How are they named this way? (page 26)

5. Octanoic acid is a fatty acid with the formula CH3(CH2)6COOH. Draw the structure of molecule and explain why it is called a saturated fatty acid.

6. Draw the generalized structure of an amino acid. Label and annotate the diagram to show the different groups that comprise amino acids. (Slide 32/Page 24)


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2.1.S2 Identification of biochemicals such as sugars, lipids or amino acids from molecular diagrams.

7. Which type of molecule is shown in the diagram to the right?

8. The diagrams below show various molecular structures. a. Identify which of the diagrams

represent: i. the structure of glucose.

ii. the structure of an amino acid.

iii. the structure of fatty acids.

b. Discuss which of the molecules are most similar in structure.

CH C

C

C

CC

C

H

HH

HH

HH

N C

R

C

O

OH

H

CH OH

C

H

HOH C

C

OH

H

C

H

OH

C

H

OH

OO

O

OH

OH

OH

OH

OH

(CH )3 2

2

n

I.

III.

II.

IV.2


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2.1.U5 Anabolism is the synthesis of complex molecules from simpler molecules including the formation of macromolecules from monomers by condensation reactions. 2.1.U6 Catabolism is the breakdown of complex molecules into simpler molecules including the hydrolysis of macromolecules into monomers. (Slide 37-41/Page 24) 9. Distinguish between the terms anabolism and catabolism.

anabolism catabolism

synthesis or breakdown?

type of reaction

substrates

products

water produced or used?

enzymes/agent involved

10. Annotate the diagram below to complete your notes on anabolism and catabolism. In the carbohydrate section add a named example, include both the names of the molecules and enzymes.


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2.1.A1 Urea as an example of a compound that is produced by living organisms but can also be artificially synthesized. (Slide 21-22/Page 17/worksheet #38) 11. Vitalism is a theory that nowadays has no credit.

a. Describe the central tenant that Wöhler falsified.

b. Wöhler accidentally artificially synthesised urea, hence falsifying vitalism. What compound was he trying to produce?

c. Accidental discoveries are a surprisingly common part of the development of scientific understanding. Referring to the IB guide identify which ‘Nature of Science’ points this example applies to.


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2.2.U.1 Water molecules are polar and hydrogen bonds form between them.

2.2.U.2 Hydrogen bonding and dipolarity explain the cohesive, adhesive, thermal and solvent properties of water.

Students should know at least one example of a benefit to living organisms of each property of water. Transparency of water and maximum density at 4°C do not need to be included.

2.2.U.3 Substances can be hydrophilic or hydrophobic.

2.2.A.1 Comparison of the thermal properties of water with those of methane.

Comparison of the thermal properties of water and methane assists in the understanding of the significance of hydrogen bonding in water.

2.2.A.2 Use of water as a coolant in sweat.

2.2.A.3 Modes of transport of glucose, amino acids, cholesterol, fats, oxygen and sodium chloride in blood in relation to their solubility in water.


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2.2.U1 Water molecules are polar and hydrogen bonds form between them. 12. Draw a minimum of three molecules to show the hydrogen bonding between them. The diagram should

be labelled and annotated to indicate: (Slide 32/Page 24)

• Large oxygen atom • Small hydrogen atom • Covalent bond – due to the larger size and greater +ve charge of the oxygen atom the shared

electrons reside closer to the oxygen nuclei. This leads to the imbalance of charges in the molecule as a whole.

• δ+ (indicate the region of each molecule which possesses a slightly positive charge ) • δ- (indicate the region of each molecule which possesses a slightly negative charge) • The imbalance of charges in a water molecule results in water being a polar molecule • Weak hydrogen bond between δ+ and δ- parts of neighbouring water molecules.

13. Explain why the water molecule is polar. Refer to electrons and covalent bonding in your answer.

(Slide 44/Page 18/worksheet 39)


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2.2.U2 Hydrogen bonding and dipolarity explain the cohesive, adhesive, thermal and solvent properties of water. 14. Summarise the key points on each property of water and how it relates to the structure of the water

molecule. Also give examples of the importance it has to organisms. Each example should use one or more of the following phrases/terms: coolant, medium for metabolic reactions and transport medium.

Outline the

property Explain how the property is due to either hydrogen bonding or dipolarity

Give examples of how organisms exploit this property

Cohesive


Adhesive (Slide 49/Page 19/worksheet 40)

Thermal



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Solvent (Slide 50/Page 19/worksheet 40)


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2.2.U3 Substances can be hydrophilic or hydrophobic. 15. Define the terms:

a. Hydrophilic (Slide 51/Page 18)

b. Hydrophobic (Slide 52/Page 18)

16. Complete the table to give examples of hydrophilic and hydrophobic molecules.

Polar, non-polar, charged? Examples

Hydrophilic

Hydrophobic

2.2.A3 Modes of transport of glucose, amino acids, cholesterol, fats, oxygen and sodium chloride in blood in relation to their solubility in water.

Complete the table to describe the transport of key substances in the blood. (Page 18) 17.

Describe the solubility in water Relate how it is carried in the blood to the solubility

Glucose (Slide 54)

Amino acids (Slide 55)

Cholesterol (Slide 56)

Fats (Slide 56)

Oxygen (Slide 57)


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2.2.A2 Use of water as a coolant in sweat. (Slide 46/page 19)

18. Outline the consequences, to cells, of not cooling the human body.

19. What property of water means it is useful as a coolant?

20. Explain how the body exploits this property of water to cool the body using sweat.

2.2.A1 Comparison of the thermal properties of water with those of methane. (Slide 47/page 18) 21. Complete the table to compare the thermal properties of water with methane.

Methane Water

Formula H

2O

Molecular mass 16 Bonding Single covalent

Polarity polar

Density (g cm-3) 0.46

Specific Heat Capacity (J g-1 oc

-1) 2.2

Latent heat of vapourisation (J g-1)

Melting point (oC) 0

Boiling point (oC) 100


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22. Referring to the table on page 13 outline how the polarity of water has affected the thermal properties of water and its ability to remain a liquid at most temperatures found on the surface of the planet.


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2.3.U.1 Monosaccharide monomers are linked together by condensation reactions to form disaccharides and polysaccharide polymers.

Sucrose, lactose and maltose should be included as examples of disaccharides produced by combining monosaccharides. The structure of starch should include amylose and amylopectin.

2.3.U.2 Fatty acids can be saturated, monounsaturated or polyunsaturated.

Named examples of fatty acids are not required.

2.3.U.3 Unsaturated fatty acids can be cis or trans isomers.

2.3.U.4 Triglycerides are formed by condensation from three fatty acids and one glycerol.

2.3.A.1 Structure and function of cellulose and starch in plants and glycogen in humans.

2.3.A.2 Scientific evidence for health risks of trans fats and saturated fatty acids.

2.3.A.3 Lipids are more suitable for long-term energy storage in humans than carbohydrates.

2.3.A.4 Evaluation of evidence and the methods used to obtain the evidence for health claims made about lipids.

2.3.S.1 Use of molecular visualization software to compare cellulose, starch and glycogen.

2.3.S.2 Determination of body mass index by calculation or use of a nomogram.


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2.3.U1 Monosaccharide monomers are linked together by condensation reactions to form disaccharides and polysaccharide polymers. 23. Condensation of monosaccharides is a polymerization reaction. It can continue to create a longer chain

of saccharides (a carbohydrate). These building reactions are part of the anabolic metabolism. a. Define polymer. (Slide 72/page 20/worksheet 41)

b. Monosaccharides are quickly and absorbed and readily used in cell respiration to release energy List the three key examples of 6-carbon monosaccharides. (Slide 62,63 &65/page 20/worksheet 41)

•

•

•

c. Annotate and complete diagram below to outline how two monosaccharides are converted into a

disaccharide through condensation, producing a glycosidic bond. Include a word equation. (Slide 67/page 19/worksheet 42)

d. What else is needed to make the reaction occur? (Hint: enzymes?... example)


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24. Complete the table to summarise the common forms of disaccharides. (Slide 68,69&70/page 20)

Disaccharide Produced by plants or animals?

Produced from which Monosaccharides?

Commonly found in

plant

Lactose animal milk

glucose + fructose sugar beet and sugar cane

2.3.A1 Structure and function of cellulose and starch in plants and glycogen in humans.

25. All three common polysaccharides are formed by the condensation of glucose molecules. Their properties however are markedly different complete the table to summarise how and why. (worksheet 43 & 44/internet)

Polysaccharide

Cellulose Starch

Glycogen Amylose Amylopectin

Size / number of glucose

molecules

variable, typically 1,500 units

Orientation and / or bonding of

glucose molecules

1-4 bonds between alternately oriented (upwards and downwards) glucose molecules

chain - straight or bent? bent

chain - branched or un-branched? branched

Properties of the molecule

• Insoluble, does not affect the osmotic balance of cells

• Molecule vary in size , easy to add / remove glucose units


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Function/use

• Useful for glucose, and consequently energy, storage, e.g. in seeds and storage organs such as potato cells.

• Temporary store in leaf cells when glucose is being made faster by photosynthesis than it can be exported.


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2.3.S1 Use of molecular visualization software to compare cellulose, starch and glycogen. 26. The easiest way to use jmol is to use the ready-made models from on the Biotopics website

(http://www.biotopics.co.uk/jsmol/glucose.html#). Play with the models, move them and zoom in and out. a. Select the the glucose molecule and identify the colours used to represent carbon, hydrogen and

oxygen atoms

Carbon –

Hydrogen –

Oxygen –

b. Using the models identify and describe the differences between glucose, sucrose and fructose

(hint: descriptions will be clearest if you refer to the numbered carbon atoms, see 2.3.U1)

c. Look at the amylose model and zoom out from it. Describe the overall shape of the molecule.

d. Zoom in on the amylose molecule. Each glucose sub-unit is bonded to how many other sub-units? Which carbons atoms used to form the glycosidic bonds? Are there any exceptions to these rules?

e. Select the amylopectin model and zoom in on the branch point. This glucose sub-unit is bonded how many others and which carbon atoms are used for bonded compared with the un-branched amylose molecule?


http://www.biotopics.co.uk/jsmol/glucose.html

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f. Using a similar approach to that above investigate the structure of glycogen and find the similarities and differences between it and both amylose and amylopectin.

2.3.U2 Fatty acids can be saturated, monounsaturated or polyunsaturated. 27. Fatty acids in the production of lipids.

a. In the space below, draw the generalized structure of a fatty acid. (Slide 82/page 22/worksheet 45)

b. Describe the term saturated when used in reference to fatty acids. (Slide 84/page 22/worksheet 45)

c. For each of the following fatty acids deduce whether it is saturated, monounsaturated or

polyunsaturated, Give reasons for each answer. • Oleic Acid

• Caproic Acid


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• α-Linolenic Acid

d.

2.3.U3 Unsaturated fatty acids can be cis or trans isomers. 28. Unsaturated fatty acids are described as being cis or trans isomers depending on the structure of the

double bonds in the fatty acids. (Slide 86) a. Complete the table to compare and contrast cis and trans isomers.

Cis-isomers Trans-isomers

Structural diagram

Natural / synthesised

Very common in nature Rare in nature – usually artificially produced to produce solid fats, e.g. margarine from vegetable oils.

Positioning of the hydrogen atoms

Shape of the fatty acid chain

The double bond causes a bend in the fatty acid chain

Packing of the fatty acids (density)

Trans-isomers can be closely packed

Triglyderides formed are liquid or solid at room temperature?


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a. Identify which isomer is cis and which is trans. Give reasons for your decisions.

2.3.A4 Evaluation of evidence and the methods used to obtain the evidence for health claims made about lipids. (Slide 95-97/page 23/worksheet 46) 29. What does the term evaluation mean?

30. Describe the key considerations for strengths.

______ -

______ -


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31. Describe the key considerations for limitations

32. Read the analysis on the article on “Health Warning: Exercise Makes You Fat” published on Bad Science (http://www.badscience.net/2009/08/health-warning-exercise-makes-you-fat/).

a. Is the health claim a valid one?

b. Review the analysis and identify which key considerations of strengths and limitations were addressed.


http://www.badscience.net/2009/08/health-warning-exercise-makes-you-fat/

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2.3.A2 Scientific evidence for health risks of trans fats and saturated fatty acids. 33. There have been many claims about the effects of different types of fat on human health. The main

concern is coronary heart disease (CHD). (Slide 97/page 23) a. Outline Identify the causes and effects of CHD.

b. Discuss the evidence that CHD is caused by a diet high in trans fats and saturated fatty acids.


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2.3.U4 Triglycerides are formed by condensation from three fatty acids and one glycerol. 34. Triglycerides are a common type of lipid formed from three fatty acids and one glycerol.

a. Draw the generalized structure of a glycerol molecule(Slide 83/page 22/worksheet 45)

b. Annotate and complete diagram below to outline how three fatty acids and one glycerol molecule are converted into a triglyceride through condensation, producing ester bonds. Include a word equation. (Slide 83/page 22/worksheet 45)


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2.3.A3 Lipids are more suitable for long-term energy storage in humans than carbohydrates. 35. Lipids are normally used for long-term energy storage whereas carbohydrates are used for short-term

energy storage. (Slide 92-94/page 23/worksheet 45) a. When the energy in carbohydrates is released what is produced?

b. The chemical energy stored in the form of glucose is for immediate use in what process?

c. Glycogen is the medium-term energy storage molecule in animals. • Where is it stored?

• Why is it used in preference to lipids?

d. The lipids used in energy storage are fats. Where and how are they stored in humans and other

mammals?

e. Explain the advantages that lipids have over carbohydrates in long-term energy storage:


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2.3.S2 Determination of body mass index by calculation or use of a nomogram. (Slide 98-100/page 23/worksheet 46) Body Mass Index (BMI) is used as a screening tool to identify possible weight problems, however, BMI is not a diagnostic tool. To determine if excess weight is a health risk further assessments are needed such as:

• skinfold thickness measurements • evaluations of diet • physical activity • and family history

BMI is calculated the same way for both adults and children. The calculation is based on the following formula:

BMI = mass in kilograms (height in metres)2

n.b. units for BMI are kg m-2

The BMI status of someone can be assessed using the table to the right. 36. A man has a mass of 75 kg and a height of 1.45 metres.

a. Calculate his body mass. (1)

b. Deduce the body mass status of this man using the table. (1)

c. Outline the relationship between height and BMI for a fixed body mass. (1)

BMI Status

Below 18.5 Underweight

18.5 – 24.9 Normal

25.0 – 29.9 Overweight

30.0 and Above Obese


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37. A woman has a height of 150 cm and a BMI of 40. a. Calculate the minimum amount of body mass she must lose to reach normal body mass status.

Show all of your working. (3)

b. Suggest two ways in which the woman could reduce her body mass. (2)

38. Use the nomogram to answer the following questions.

a. A women has a mas of 75 Kg and a height of 160cm. Determine her BMI status.

b. A man is 190cm tall and has an acceptable BMI. Estimate his body mass.


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http://helid.digicollection.org/documents/h0211e/p434.gif





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Understandings, Applications and Skills (This is what you may be assessed on) Statement Guidance

2.4 U.1 Amino acids are linked together by condensation to form polypeptides.

2.4 U.2 There are 20 different amino acids in polypeptides synthesized on ribosomes.

Students should know that most organisms use the same 20 amino acids in the same genetic code although there are some exceptions. Specific examples could be used for illustration.

2.4 U.3 Amino acids can be linked together in any sequence giving a huge range of possible polypeptides.

2.4 U.4 The amino acid sequence of polypeptides is coded for by genes.

2.4 U.5 A protein may consist of a single polypeptide or more than one polypeptide linked together.

2.4 U.6 The amino acid sequence determines the three-dimensional conformation of a protein.

2.4 U.7 Living organisms synthesize many different proteins with a wide range of functions.

2.4 U.8 Every individual has a unique proteome.

2.4 A.1 Rubisco, insulin, immunoglobulins, rhodopsin, collagen and spider silk as examples of the range of protein functions.

The detailed structure of the six proteins selected to illustrate the functions of proteins is not needed.

2.4 A.2 Denaturation of proteins by heat or by deviation of pH from the optimum.

Egg white or albumin solutions can be used in denaturation experiments.

2.4 S.1 Drawing molecular diagrams to show the formation of a peptide bond.


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2.4.U1 Amino acids are linked together by condensation to form polypeptides. AND 2.4.S1 Drawing molecular diagrams to show the formation of a peptide bond. (Slide 107/page 24/worksheet 47) 39. Condensation of amino acids is a polymerisation reaction. A chain of amino acids joined together is

called a polypeptide. These building reactions are part of the anabolic metabolism. a. What structure mediates and controls the formation of polypeptides?

b. Apart from the above structure what else is needed for the reaction to occur? (Hint: enzymes?... example)

c. Draw and annotate a structural diagram below to outline how two generalised amino acids (i.e. use the R-group nomenclature) into a dipeptide through condensation, producing a peptide bond.

2.4.U2 There are 20 different amino acids in polypeptides synthesized on ribosomes. (Slide 109-115/page 24/worksheet 47) 40. How many different amino acids do we know of?

41. How many of these amino acids are synthesized by ribosomes?


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42. List three examples of amino acids synthesised by ribosomes. Slide 123/worksheet 47)

•

•

•

42. Extension: Outline the process by which the remaining amino acids are created. (Hint: Proteomes)

2.4.U3 Amino acids can be linked together in any sequence giving a huge range of possible polypeptides. 43. State the three key ideas that explain the huge range of possible polypeptides: (Slide 111-113/page 25/worksheet 48)

•

•

•

43. If a polypeptide contains just 5 amino acids calculate the how many different polypeptides can be

created.

44. State both the name of the longest polypeptide known and approximately how many amino acids it contains.(Hint: Coverpage)

2.4.U4 The amino acid sequence of polypeptides is coded for by genes. 45. Outline the central dogma of genetics. (Slide 115/worksheet 48)


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2.4.U6 The amino acid sequence determines the three-dimensional conformation of a protein. 2.4.U5 A protein may consist of a single polypeptide or more than one polypeptide linked together.

46. The R-groups of an amino acid are classified as having one of a number of different properties. List the

properties can they possess. (Slide 108/page 25/worksheet 47)

•

•

•

•

n.b. the below question is helpful to SL students for a more complete understanding, but is required knowledge for HL students as it covers 7.3.U7 to 7.3.U10

47. Outline the four different levels of protein structure. (n.b. although you don’t need to be able to outline

the different levels of structure knowing of them helps to understand the different functions proteins have and why)

Notes Fibrous or Globular Primary

(polypeptide) • The order / sequence of the amino acids of which the

protein is composed

• Formed by covalent peptide bonds between adjacent

amino acids

• Controls all subsequent levels of structure

Neither (– will fold to

become one of the

subsequent levels of

structure)

Secondary (Slide 117/page 96-97/worksheet

219)

Tertiary (Slide 120/page 96-97/worksheet

219)

Quaternary (Slide 121/page 96-97/worksheet


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219)


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48. Distinguish between globular and fibrous proteins (Slide 123)

Fibrous Globular

Location of R groups

Shape

Function

Solubility

Amino acid sequence

Stability

Examples


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2.4.U7 Living organisms synthesize many different proteins with a wide range of functions. 2.4.A1 Rubisco, insulin, immunoglobulins, rhodopsin, collagen and spider silk as examples of the range of protein functions. 49. Complete the table to describe each of different functions that proteins have in and outside of cells.

(Slide 125-132/page 25/worksheet 49)

Function Description Key examples

Rubisco

Muscle contraction

Tubulin is the subunit of microtubules that give animals cells their

shape and pull on chromosomes during mitosis.

collagen

Blood clotting

Proteins in blood help transport oxygen, carbon dioxide, iron and

lipids.

Cell adhesion

Membrane transport

Insulin

Receptors

rhodopsin

Packing of DNA

This is the most diverse group of proteins, as cells can make huge

numbers of different antibodies. immunoglobulins


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2.4.U8 Every individual has a unique proteome. 50. The proteome is unique to every individual.

a. Define the term genome. (Slide 134/page 38)

b. Define the term proteome. (Slide 133/page 24)

c. Aside from the genome what affects the proteome? (Slide 133/page 24)


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d. Explain why the proteome is larger and more varied that the genome.

2.4.A2 Denaturation of proteins by heat or by deviation of pH from the optimum. (Slide 136/page 25/worksheet 48) 51. Describe the term denaturation. Refer to the structure of the protein in your answer.

52. What factors can commonly cause denaturation and how?


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Understandings, Applications and Skills (This is what you may be assessed on) Statement Guidance

2.6.U.1 The nucleic acids DNA and RNA are polymers of nucleotides.

2.6.U.2 DNA differs from RNA in the number of strands present, the base composition and the type of pentose.

2.6.U.3 DNA is a double helix made of two antiparallel strands of nucleotides linked by hydrogen bonding between complementary base pairs.

2.6.A.1 Crick and Watson’s elucidation of the structure of DNA using model making.

2.6.S1 Drawing simple diagrams of the structure of single nucleotides of DNA and RNA, using circles, pentagons and rectangles to represent phosphates, pentoses and bases.

In diagrams of DNA structure, the helical shape does not need to be shown, but the two strands should be shown antiparallel. Adenine should be shown paired with thymine and guanine with cytosine, but the relative lengths of the purine and pyrimidine bases do not need to be recalled, nor the numbers of hydrogen bonds between the base pairs.


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2.6.U1 The nucleic acids DNA and RNA are polymers of nucleotides. (includes 2.6.S1 Drawing simple diagrams of the structure of single nucleotides of DNA and RNA, using circles, pentagons and rectangles to represent phosphates, pentoses and bases.) (Slide 145-146/ worksheet 54) 53. Label and annotate the structures of this single nucleotide.

a.

b.

c.

54. State the =type of bond that joins a to b and b to c.

55. Complete the table below to show the pairings of the bases in DNA and RNA.

Purine Pyramidine

56. In the space below, draw a single strand of three nucleotides, naming the bonds between them and

showing the correct relative position of these bonds.


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57. Annotate the diagram above to outline the process of polymerisation of nucleotides to form a strand of DNA/RNA. (Slide 148/page 28/worksheet 54)

2.6.U2 DNA differs from RNA in the number of strands present, the base composition and the type of pentose. 58. Complete the table to distinguish between RNA and DNA.

RNA DNA

Bases

Adenine (A) Guanine (G) Uracil (U)

Cytosine (C)

Sugar

Number of strands Two anti-parallel,

complementary strands form a double helix

2.6.U3 DNA is a double helix made of two antiparallel strands of nucleotides linked by hydrogen bonding between complementary base pairs. (includes 2.6.S1 Drawing simple diagrams of the structure of single nucleotides of DNA and RNA, using circles, pentagons and rectangles to represent phosphates, pentoses and bases.) 59. In the space below, draw a section of DNA, showing two anti-parallel strands of four nucleotides each.

Label the bonds which hold the bases together as well as the correct complementary base pairs. Extension: include the carbon numbering on the deoxyribose sugars and indicate the 5-prime and 3-prime ends of the molecule (though not needed at this point this is useful for DNA replication, transcription and translation)


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60. Define the term double helix. (Slide 149/ page 28/worksheet 54)

61. Explain why the DNA helix is described as anti-parallel.

62. Explain the relevance of the following in the double-helix structure of DNA: (Slide 143-150/ page 28/worksheet 54) a. Complementary base pairing

b. Hydrogen bonds

c. Relative positioning of the sugar-phosphate backbone and the bases


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2.6.A1 Crick and Watson’s elucidation of the structure of DNA using model making. 63. Whilst others worked using an experimental basis Watson and Crick used stick-and-ball models to test

their ideas on the possible structure of DNA. (Slide 151/ page 28) a. State two benefits of modelling over an experimental approach.

b. Outline the reasons was their first model was rejected.

c. Because of the visual nature of Watson and Crick’s correct model of DNA led to other discoveries.

List the two key discoveries concerning of DNA that were found quickly after the model was published.

•

•

d. Modelling alone cannot led to discoveries. Watson and Crick’s work was based on the experiments

and insight of others. Give an example of the work of other scientists that supported their discovery.

Citations:

Allott, Andrew. Biology: Course Companion. S.l.: Oxford UP, 2014. Print. Paine, Chris http://bioknowledgy.weebly.com Taylor, Stephen. "Essential Biology 03.3 07.1 DNA Structure.docx." Web. 1 Oct. 2014.


Topic 2 biochem student notes 2015

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Transcript of Topic 2 biochem student notes 2015