AQA · A-Level · Biology

    Course version: 7402 · Version from Sept 2016

    The arrangement and any movement of phospholipids, proteins, glycoproteins…

    Full specification wording

    Transport across cell membranes: The arrangement and any movement of phospholipids, proteins, glycoproteins and glycolipids in the fluid-mosaic model of membrane structure.

    Fluid refers to the lateral movement of phospholipids, proteins, glycoproteins, and glycolipids within the membrane, giving it flexibility to bend and fuse.

    Checked against the AQA 7402 specification (opens in a new tab) on .

    • Point 2 of 8
    • 4 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    Fluid refers to the lateral movement of phospholipids, proteins, glycoproteins, and glycolipids within the membrane, giving it flexibility to bend and fuse. Mosaic refers to the scattered arrangement of proteins. Phospholipids form a bilayer. Intrinsic proteins span the bilayer; their hydrophobic R groups face the fatty acid tails, while hydrophilic R groups line central channels for water-soluble substances, or act as receptors. Extrinsic proteins sit on one surface. Glycoproteins and glycolipids project from the outer surface for cell recognition. While many molecules move laterally, some proteins are anchored.

    What earns the marks

    • Phospholipids, proteins, glycoproteins and glycolipids being able to move laterally, making the membrane fluid.
    • Proteins scattered through the bilayer in a mosaic, with some spanning it and some on one surface.
    • Hydrophobic regions of an intrinsic protein lying next to the fatty acid tails.
    • Hydrophilic regions forming a channel for ions or polar molecules.
    • Glycoproteins and glycolipids projecting from the outer surface for cell recognition.

    Common mistakes and how to put them right

    • Placing glycoproteins and glycolipids on both faces of the membrane, or on the inner face.

    • Describing proteins as floating on top of the bilayer rather than embedded in or spanning it.

    • Stating all spanning proteins are transport proteins, ignoring that many are integral receptors.

    • Saying the membrane is fluid because liquid passes through it.

    Exam tips

    • Explain fluid and mosaic separately; each word usually carries its own mark.
    • When describing intrinsic proteins, mention both hydrophobic regions facing tails and hydrophilic regions lining channels.

    Try the lesson

    The start of the Transport across cell membranes: The arrangement and any movement of phospholipids, proteins, glycoproteins and glycolipids in the fluid-mosaic model of membrane structure. lesson, made from checked teaching notes for this specification point.

    Have a go first

    In the fluid-mosaic model of membrane structure, what forms the bilayer?

    Listen

    Fluid refers to the lateral movement of phospholipids, proteins, glycoproteins, and glycolipids within the membrane, giving it flexibility to bend and fuse. Mosaic refers to the scattered arrangement of proteins. Phospholipids form a bilayer. Intrinsic proteins span the bilayer; their hydrophobic R groups face the fatty acid tails, while hydrophilic R groups line central channels for water-soluble substances, or act as receptors. Extrinsic proteins sit on one surface. Glycoproteins and glycolipids project from the outer surface for cell recognition. While many molecules move laterally, some proteins are anchored. A strong answer earns marks for these points. phospholipids, proteins, glycoproteins and glycolipids being able to move laterally, making the membrane fluid. proteins scattered through the bilayer in a mosaic, with some spanning it and some on one surface. hydrophobic regions of an intrinsic protein lying next to the fatty acid tails. hydrophilic regions forming a channel for ions or polar molecules. Exam tip: Explain fluid and mosaic separately; each word usually carries its own mark.

    See it

    A flowchart starting from a phospholipid bilayer node. From it, one branch leads to phospholipids moving laterally, which leads to the membrane being fluid, giving flexibility to bend and fuse. Another branch leads to proteins scattered through the bilayer, labelled as the mosaic arrangement; this splits into intrinsic proteins spanning the bilayer and extrinsic proteins sitting on one surface. Intrinsic proteins split into hydrophobic R groups facing the fatty acid tails and hydrophilic R groups lining central channels or acting as receptors. A further branch from the bilayer leads to glycoproteins and glycolipids projecting from the outer surface, which leads to cell recognition.
    It shows the arrangement and lateral movement of phospholipids, proteins, glycoproteins and glycolipids in the fluid-mosaic model.

    Key words

    Say what each word means before you turn the card.

    fluid-mosaic model

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    lateral movement of membrane components

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    intrinsic and extrinsic proteins

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    glycoproteins and glycolipids

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    See every definition
    fluid-mosaic model
    The arrangement and any movement of phospholipids, proteins, glycoproteins and glycolipids in the membrane.
    lateral movement of membrane components
    Phospholipids, proteins, glycoproteins and glycolipids able to move laterally, giving the membrane flexibility to bend and fuse.
    intrinsic and extrinsic proteins
    Proteins scattered through the bilayer, with some spanning it and some sitting on one surface.
    glycoproteins and glycolipids
    Molecules projecting from the outer surface for cell recognition.

    Label the diagram

    Some boxes have lost their names. Pick the right name for each number.

    The diagram again, with 3 boxes numbered instead of named. A flowchart starting from a phospholipid bilayer node. From it, one branch leads to phospholipids moving laterally, which leads to the membrane being fluid, giving flexibility to bend and fuse. Another branch leads to proteins scattered through the bilayer, labelled as the mosaic arrangement; this splits into intrinsic proteins spanning the bilayer and extrinsic proteins sitting on one surface. Intrinsic proteins split into hydrophobic R groups facing the fatty acid tails and hydrophilic R groups lining central channels or acting as receptors. A further branch from the bilayer leads to glycoproteins and glycolipids projecting from the outer surface, which leads to cell recognition.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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