Biology  by Bradford
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B1.2 Proteins: revision map

The subtopic in the middle and ten tasks round it: label four diagrams, complete two tables, put a process in order and fill 49 gaps. Every standard level statement has a box; the five boxes for higher level only are dashed and badged HL, and drop off for an SL class. Type into the blanks and check them, or print it on A4, Letter or A3 with an answer key.

B1.2 practice questionsThe whole B1 map

B1.2

Proteins

Molecules · Form and functionName

B1.2.1An amino acid

NCHCOOHHH1234
  1. 1
  2. 2
  3. 3
  4. 4

B1.2.9Holding the foldHL

SS+−1234
  1. 1
  2. 2
  3. 3
  4. 4

This folding of the whole chain is the structure. Only one of the four links shown is covalent: it joins the R-groups of two amino acids. Amine and carboxyl groups in R-groups become charged by gaining or losing .

B1.2.11, B1.2.12Proteins comparedHL

Polypeptide chainsShape
Insulin2
Collagen
Haemoglobin

Haemoglobin is a protein: each of its chains carries a non-polypeptide group. Insulin and collagen are not. Compact and soluble, insulin travels in the blood to its target cells; the long, rope-like chains of collagen give to skin, tendons and bone.

B1.2.2Joining amino acids

NCCNCCHHHOHHOOH

Two amino acids link in a reaction: amino acid + amino acid → + . The shaded bond, from the carbon of one to the nitrogen of the next, is a . More links like it build a .

B1.2.3What we must eat

Amino acids the body cannot make for itself are : they must come from food. amino acids can be made from other amino acids. Some plant foods are low in one or more of the first kind, so a diet needs a varied mix of protein sources.

B1.2Proteins

B1.2.6, B1.2.10Variety in R-groupsHL

Every R-group is either hydrophobic or ; the second kind are either or charged, and charged ones are acidic or . In a protein dissolved in water, hydrophobic R-groups cluster in the , away from water, while an integral protein has bands of them where it sits in the .

B1.2 examA simplified model of a haemoglobin moleculeHL

A simplified model of a haemoglobin molecule1234
  1. 1
  2. 2
  3. 3
  4. 4

B1.2.4Counting sequences

Amino acids in the chainPossible sequences
120
2
3
n

Chains run from a few amino acids to many , in any order, so the number of possible polypeptides is practically .

B1.2.5Heating a protein

Number the steps in order.

  1. Its atoms vibrate more and more strongly.
  2. The temperature rises far above the protein's normal range.
  3. Bonds holding the folded chain in place break.
  4. The chain unfolds and loses its precise three-dimensional shape.
  5. The protein can no longer do its job, and usually stays that way when it cools.

This change is . Extremes of cause it too, by altering the charges on R-groups.

B1.2.7, B1.2.8Regular foldsHL

123
  1. 1
  2. 2
  3. 3

The order of amino acids, the structure, decides where these folds form and how the whole chain folds up, so every copy of a protein has the same precise . These folds are its structure, held by bonds between C=O and N–H groups at regular intervals.

Word bank 20ⁿ344008000alpha carbonalpha helixalpha-helixamine groupbasicbeta-pleated sheetcarboxyl groupcondensationconjugatedcorecysteinedenaturationdipeptidedisulfide bondessentialfibrousglobularH⁺haemhydrogen bondhydrophilichydrophobic interactionsinfiniteionic bondironmembraneNon-essentialpeptide bondpHpolarpolypeptideprimaryR-groupsecondaryshapetensile strengthtertiarythousandsveganwater

Answer key

Every box on the sheet with its gaps filled in, as the subtopic reads in full.

  1. LabelAn amino acid

    1. amine group
    2. alpha carbon
    3. R-group
    4. carboxyl group

  2. GapsJoining amino acids

    Two amino acids link in a condensation reaction: amino acid + amino acid → dipeptide + water. The shaded bond, from the carbon of one to the nitrogen of the next, is a peptide bond. More links like it build a polypeptide.

  3. GapsWhat we must eat

    Amino acids the body cannot make for itself are essential: they must come from food. Non-essential amino acids can be made from other amino acids. Some plant foods are low in one or more of the first kind, so a vegan diet needs a varied mix of protein sources.

  4. TableCounting sequences

    Amino acids in the chainPossible sequences
    120
    2400
    38000
    n20ⁿ

    Chains run from a few amino acids to many thousands, in any order, so the number of possible polypeptides is practically infinite.

  5. OrderHeating a protein

    1. The temperature rises far above the protein's normal range.
    2. Its atoms vibrate more and more strongly.
    3. Bonds holding the folded chain in place break.
    4. The chain unfolds and loses its precise three-dimensional shape.
    5. The protein can no longer do its job, and usually stays that way when it cools.

    This change is denaturation. Extremes of pH cause it too, by altering the charges on R-groups.

  6. GapsVariety in R-groups HL

    Every R-group is either hydrophobic or hydrophilic; the second kind are either polar or charged, and charged ones are acidic or basic. In a protein dissolved in water, hydrophobic R-groups cluster in the core, away from water, while an integral protein has bands of them where it sits in the membrane.

  7. LabelRegular folds HL

    1. alpha helix
    2. beta-pleated sheet
    3. hydrogen bond

    The order of amino acids, the primary structure, decides where these folds form and how the whole chain folds up, so every copy of a protein has the same precise shape. These folds are its secondary structure, held by bonds between C=O and N–H groups at regular intervals.

  8. LabelHolding the fold HL

    1. disulfide bond
    2. ionic bond
    3. hydrogen bond
    4. hydrophobic interactions

    This folding of the whole chain is the tertiary structure. Only one of the four links shown is covalent: it joins the R-groups of two cysteine amino acids. Amine and carboxyl groups in R-groups become charged by gaining or losing H⁺.

  9. TableProteins compared HL

    Polypeptide chainsShape
    Insulin2globular
    Collagen3fibrous
    Haemoglobin4globular

    Haemoglobin is a conjugated protein: each of its chains carries a non-polypeptide haem group. Insulin and collagen are not. Compact and soluble, insulin travels in the blood to its target cells; the long, rope-like chains of collagen give tensile strength to skin, tendons and bone.

  10. Exam diagramA simplified model of a haemoglobin molecule HL

    1. alpha-helix
    2. haem
    3. iron
    4. polypeptide