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ocr as/a level biology a > Module 2.5 Biological Membranes > Flashcards

Module 2.5 Biological Membranes Flashcards

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AP® Biology flashcards
1
Q

How thick are membranes?

A

7-10nm

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2
Q

Describe the phospholipid bilayer

A

Hydrophilic phosphate heads make up outside
Hydrophobic fatty acid tails make up inside
2 layers of phospholipid make up the bilayer

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3
Q

Is the phosphate head evenly charged?

A

No

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4
Q

Intrinsic protein

A

Spans whole bilayer

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5
Q

Extrinsic protein

A

Partially embedded inside or outside

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6
Q

Glycolipids and glycoproteins

A 
For cell signalling 
Allow self recognition 
Receptors for drugs + hormones
Antigens 
Glycoproteins can bind cells in tissues
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7
Q

Channel proteins

A

Allow small ions/small water soluble molecules to diffuse through

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8
Q

Carrier proteins

A

Help large molecules to diffuse through

Used in active transport

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9
Q

Cholesterol

A

For stability and to regulate fluidity

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10
Q

Cells communicate w/hormones

A

Hormones bind to receptors (complimentary shape)

Response occurs in target cell e.g. gene/DNA activated

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11
Q

Insulin

A

Made in beta cells in the islets of langerhans in the pancreas
Released when glucose level of blood too high
Target cells are muscle tissue, adipose tissue + liver cells
Effect is glucose taken out of blood = blood glucose level lowered

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12
Q

Beta blockers

A

Stop heart muscle beating to fast which could cause a heart attack

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13
Q

Poisons

A

Bind w/receptors

Botox paralyses facial muscles

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14
Q

Hijacking receptors

A

Viruses can bind with receptors e.g. HIV and AIDS
HIV virus can bind with receptors on T-lymphocytes
Lowers immune system
HIV bursts WBCs

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15
Q

🌟Diffusion

A

Net movement
High to low conc.
Down conc. gradient
Passive process

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16
Q

🌟Osmosis

A 
Net movement of water
From high water pot. to lower water pot. 
Across partially permeable membrane
Down water pot. gradient
Passive process
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17
Q

🌟Active transport

A 
Net movement of molecules/ions
Low to high conc.
Against conc. gradient
Uses ATP
Requires energy 
Across partially permeable membrane
Needs carrier proteins/channel proteins
18
Q

Channel proteins

A

Polar molecules/ions

19
Q

Carrier proteins

A

Large molecules

20
Q

Hypertonic

A

Lots of salts and sugars

21
Q

Isotonic

A

The same water pot. in and out =no net movement

22
Q

Hypotonic

A

High water pot.

23
Q

Water pot. of pure water

A

0 kPa

24
Q

More concentrated solution

A

Lower water pot. = more negative number

25
Q

Water moves from a

A

Higher water potential (less neg. number) to a lower water potential (more neg. number)

26
Q

Water potential

A

Solute potential + pressure potential

27
Q

What happens when a cell is placed in a hypotonic solution?

A

Water moves into the cell (via osmosis)
Animal cells will burst (haemolysed)
Plant cells will become turgid (cytoplasm and vacuoles will push the membrane against the cellulose cell wall)

28
Q

What happens when a cell is placed in a hypertonic solution?

A

Water moves out of the cell (via osmosis)
Animal cells shrink (crenated)
Plant cells become plasmolysed (cell membrane pulls away form cell wall)

29
Q

🌟Basic structure of cell surface membranes

A

Phospholipids form bilayer

Hydrophobic tails pointing inwards

Hydrophilic heads pointing out

Role of phospholipids: to provide a barrier to large/polar molecules and ions

Carrier/channel proteins for active transport/facilitated diffusion

Cholesterol stabilises the membrane and regulates fluidity

Glycoproteins which act as receptors for cell communication

30
Q

🌟Roles of cell surface membranes inside cells

A

Form edge of organelles within a cell

Isolation of contents of organelles from cytoplasm

Site of attachment of enzymes and ribosomes (on RER)

Provide selective permeability - controls what enters and leaves organelles

Separates areas of differing concentration to provide gradients

31
Q

🌟Cell signalling - how receptors work

A

Release of signal molecules e.g. hormones by exocytosis into the blood

Proteins/glycoproteins/glycolipids act as receptors for hormones and drugs

The receptor is specific as the shape of the receptor and hormone are complementary in shape

The hormone binds to the receptor

Binding causes a change inside the cell which brings about a response

32
Q

🌟Role of glycoproteins

A

Cell signalling - communication between cells to help them work together

Act as antigens for…

Cell recognition - self/non-self

Receptors found on target cells

For hormones/cytokines to trigger reactions/responses in cells

Cell adhesion in tissues

Form bonds with water molecules to stabilise the membrane

Receptors on transport proteins

33
Q

🌟Small, non-polar substances

A

Diffuse through the phospholipid bilayer

34
Q

🌟Larger substances

A

Use carrier proteins

Specific to certain molecules

The protein changes shape to allow the molecule through to the other side

Facilitated diffusion/active transport (uses ATP, against gradient, faster, one way)

Endocytosis/exocytosis

Bulk transport

35
Q

🌟Polar substances

A

Through channel proteins

Facilitated diffusion

36
Q

🌟Compare active transport and facilitated diffusion

A

Active transport:

  • Carrier proteins
  • Anything from low to high conc.
  • Uses ATP
  • Only goes in one direction
  • Much quicker than diffusion

Facilitated diffusion:

  • Carrier proteins
  • Channel proteins
  • Larger molecules e.g. glucose
  • Ions/polar molecules e.g. K+ and Ca2+
  • Needed when phospholipid bilayer won’t allow large/polar/water soluble molecules to cross
  • No ATP needed
37
Q

🌟Compare the roles of carrier proteins and channel proteins and how they work

A

Carrier proteins:

  • Specific to molecule
  • Molecule attaches on one side of the membrane
  • Protein changes shape
  • Releases molecule on the other side of the membrane
  • Carries large molecules across the membrane in facilitated diffusion (doesn’t require energy)
  • Carries all molecules across the membrane in active transport (requires energy)

Channel proteins:

  • Specific to molecule
  • Forms a pore through the centre of the protein
  • Hydrophilic conditions inside the pore
  • Allows charged and polar substances across the membrane in facilitated diffusion
38
Q

🌟Facilitated diffusion

A 
Net movement 
High conc. to lower conc.
Down conc. grad.
Through carrier proteins (large molecules)
Channel proteins (ions)
Passive process
39
Q

🌟Stages of exocytosis

A

Vesicle moves towards cell surface membrane along microtubules

Vesicle fuses w cell surface membrane

Protein released out of cell by exocytosis

Movement of vesicles on microtubules and fusion of vesicles w membrane requires ATP

40
Q

🌟Stages of endocytosis

A

Molecule binds w receptor

Cell surface membrane invaginates (ATP required)

Membrane fuses w itself

Vesicle formed

Vesicle moves through cytoplasm to destination organelle

ocr as/a level biology a (14 decks)

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