Proteins in action

[Proteins in action, my goodness. This book has some weird titles.]

Quaternary structure = proteins made of more than one polypeptide

Haemoglobin - transport protein

- Globular; water-soluble

- Quaternary structure consists of four polypeptide subunits - 2 alpha-chains, 2 beta-chains — forms one haemoglobin molecule

- Function is to carry oxgyen from lungs to tissues; binds with oxygen in lungs and releases it in tissues; haem group [contains iron ion, hehehe iron ion] is responsible for colour of haemoglobin:

haemoglobin [purple-red] + oxygen —> oxyhaemoglobin [bright red]

- Oxygen molecule binds to iron in haem group - four haem groups, four oxygen molecules


Collagen - structural protein

- Fibrous; made of 3 polypeptide chains held together by hydrogen bonds [looks like twisted rope]

Function is to provide mechanical strength in many areas:

  • in walls of arteries, collagen layer prevents blood being pumped at high pressure from bursting walls
  • tendons connecting skeletal muscles to bones
  • bones
  • cartilage and connective tissue
  • cosmetic treatments - e.g. injecting into lips to give fuller appearance

this is how i spent my saturday evening!

the trickier bits of ocr a2 biology f215.

they were meant to be clouds, but my hands were aching so i didn’t cut them out properly, now they look like apoptosing cells with blebs formed.

so much content in this exam, no clue what’s going to come up.

Why would you say not to credit something and then in the next question credit it ? 



this type of shit is the reason I can’t get a good grade.

You have shit mark schemes. 

Proteins from amino acids

Amino acids —> dipeptides —> polypeptides

Polypeptides and proteins are made in cells on ribosomes - protein synthesis —> as mRNA passes through ribosome, amino acids join together one at a time [condensation reaction happening each time]

Primary structure = unique amino acid sequence

Secondary structure = coiling/pleating of polypeptide molecule [alpha helix/beta pleated sheet] - hydrogen bonds hold coils in place

Tertiary structure = final 3D shape of protein, coils coil and pleats pleat - held together by numerous bonds; tertiary structure vital to protein - hormone and hormone receptor, active site of enzyme…

The bonds:

  1. disulfide - two cysteines close to each other form a covalent bond
  2. ionic - oppositely charged amino acids
  3. hydrogen - slightly oppositely charged [+ and -] groups come close to each other
  4. hydrophobic and hydrophilic- hydrophobic amino acids tend to be found at center, surrounded by hydrophilic amino acids

Heating a protein increases kinetic energy, molecule vibrates and some bonds are broken, tertiary structure broken - denaturation

- Globular proteins - roll up into compact globe/ball shaped structure; hydrophobic R-groups turned inwards, hydrophilic R-groups on outside — makes protein water-soluble [enzymes, plasma proteins, antibodies]

- Fibrous proteins - form fibres, have regular repetitive sequences, usually insoluble [Keratin in nails and hair, collagen in bone and cartilage]

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Cells and living processes

Characteristics of living things [MRS. NERG]:

  • Movement
  • Respiration
  • Sensitivity
  • Nutrition
  • Excretion
  • Reproduction
  • Growth 

[Some bacteria don’t respire but use other chemical reactions for energy]

Ultrastructure = detailed structure of internal components of cells revealed by electron microscopes

Division of labour = different organelles working together in a cell, each contributing its part to the survival of the cell

Cytoskeleton = network of protein fibres wiithin cells that gives structure and shape to cell, also moves organelles around inside cells:

  • some fibres [actin filaments] are like muscle cell fibres - able to move against each other easily; cause movement seen in some white blood cells; move organelles around inside cells
  • other fibres [microtubules] - cylinders; made of tubulin; used to move microorganisms through liquids or to waft liquids past cell


  • In eukaryotes flagella [undulipodia] and cilia are structurally similar - hair-like extensions; each one made of a cylinder containing 9 microtubules arranged in a circle and 2 microtubules in central bundle
  • Undulipodia are longer than cilia
  • undulipodium forms tail of sperm cell - can move whole cell
  • Microtubules use energy from ATP to move
  • Some bacteria have flagella but internal structure differs - made of spiral protein [flagellin] atteched by a hook to a protein disc at base; disc rotates using ATP, flagellum spins


  • Vesicles = membrane-bound sacs found in cells; used to carry substances around cells
  • In plant cells, large vacuole maintains cell stability - filled with water and solutes so it pushes cytoplasm against cell wall, cell becomes turgid

Plant cell walls:

  • On outside of plant cell plasma membrane [cell surface membrane]
  • Made of cellulose [carbohydrate polymer made of glucose]
  • Cellulose forms sieve-like network strands that makes the wall strong
  • Held rigid by pressure of fluid inside cell [turgor pressure] - supports cell and whole plant

Antibodies = protein molecules that identify and neutralise antigens

  • produced by B lymphocytes [plasma cells] in immune system
  • released in response to infection
  • large proteins; immunoglobulins
  • specific shape complimentary to particular antigen
  • attach to antigens and render them harmless

Antigens = molecules that stimulate immune response; antibody generator

  • stimulate immune response
  • almost any molecule can act as antigen
  • large molecules with specific shape
  • stimulate production of antibodies
  • usuall a protein or glycoprotein in/on plasma membrane

! Don’t confuse antigens with pathogens - pathogen has antigens on its surface.

Specificity = antibody is specific to a particular antigen because of shape of variable region

Structure of antibody:

  • four polypeptide chains, held together by disulfide bridges
  • constant region [same in all antibodies] - allows antibody to attach to phagocytic cell
  • variable region [differs in each type of antibody; result of amino acid sequence] - complimentary to specific antigen
  • hinge regions - allow certain degree of flexibilty [to attach to more than one antigen]

So we're learning about mutations in Biology.

To get a good idea of how mutations work, we’re told to use this sentence to help us:


This sentence is used because each word has 3 letters. Letters act as nucleotide bases, and 3 nucleotide bases code for one amino acid. 

If one of the letters changes, the whole sentence has a different meaning. If one nucleotide base changes, amino acid will be different and this is called a mutation.

This is the example we’re given to help us understand this concept.


They referenced mpreg… in biology.


A science subject.