2.4 Proteins

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  • Created by: sofiedb
  • Created on: 20-02-18 16:52
Workforce of nature
enzymes, protein pumps, agents of immune system, structural function
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Polypeptides
amino acids linked by condensation reactions, nr. of peptides is the polypeptide (aka protein)
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Basic unit of polypeptides
amino acid: carbon-based compound with carboxyl group (-COOH) & amine group (NH2)
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Dipeptide
2 amino acids bind in a condensation reaction to form a dipeptide
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H2O during condensation
the carboxyl group & amine group during condensation provide the OH & H to release an H2O molecule
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Larger polypeptides
more amino acids linked together
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Amino acids in nature
20 amnio acids: linked together in any sequence to form polypeptides - 20^n polypeptides can be formed (n=nr. of amino acids per polypeptide)
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Organelle responsible for polypeptide synthesis
ribosomes (during 'translation' process)
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Genes
coding sections of the genome - contain instructions for all building blocks of an organism, code for 1 polypeptide (sequence of amino acids linked by peptide bonds) - each polypeptide has one function
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Organelles & genes/polypeptides
Genes found in nucleus & polypeptides synthesised in the cytoplasm
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mRNA
messenger RNA: molecule containing specific instructions & carries instructions for amino acid sequences to ribosome in cytoplasm
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Protein
1 polypeptide or multiple polypeptides linked
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Type of polypeptide/protein
Rubisco: found in chloroplasts & used in photosynthesis, an enzyme, many polypeptide chains
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Examples of proteins & their nr of polypeptide chains
lysozyme: 1 chain, insulin: 2 chains, collagen: 3 chains, haemoglobin: 4 chains
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Conformation of protein
order of amino acids determines the shape & function of the protein
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20 amino acid differentiating factor
the R group:determines types of bonds & interactions with other molecules they can make, defines how polypeptide chain/chains fold up in a protein, affects 3-D structure of the polypeptide (conformation)
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Change in conformation
single change in the order of amino acids causes change of shape/loss of function - can be caused by gene mutations
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Primary structure
sequence of amino acids in a protein which defines the aspects of structure & function of a protein - defines the secondary, tertiary & quaternary structures
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Secondary structure
the folding of chains on themselves to form pleated sheets/helixes (regular sub-structures)
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Tertiary structure
when a polypeptide folds & coils to form a complex 3-D shape
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Quaternary structure
occurs in proteins made up of 2+ polypeptide chains & refers to the way the multiple subunits are held together in a multi-subunit complex (complex of protein molecules)
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Protein with quaternary structure
human haemoglobin - 2 alpha & 2 beta chains, it forms the structure which transports oxygen together with the heme group
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Proteome
unique set of proteins in an organism coded by the genome (protein + genome: proteome)
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Proteome analysis
new tool in medical research & cancer treatment (determining chemotherapy)
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Human genome
consists of more/codes for more proteins than a yeast genome, making it more complex
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Protein forms
globular & fibrous
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Globular proteins
globe-like/spherical, have active roles in cell's metabolism, consist of complex polypeptide chains (can be linked to other chains to form large, complex proteins), soluble in water (hydrophobic R groups folded into core of molecule, away from H2O)
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Fibrous proteins
long & thread-like, consist of long polypeptide chains where hydrophobic R groups are exposed making it insoluble, found in structural parts of the organism (e.g. tendons)
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Globular protein examples
Rubisco, insulin, immunoglobulin, rhodopsin
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Fibrous proteins examples
collagen, spider silk
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Rubisco function
enzyme: fixation of CO2 in chloroplasts
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Insulin function
hormone: produced in the pancreas by beta cells, glucose uptake from blood
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Immunoglobulin function
y-shaped antibodies: fight infections by recognising & binding to antigen molecules
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Rhodopsin function
linked to pigment: found on membrane of rod (photoreceptor) cells of retina - allow low light intensities to be detected
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Collagen function
structural protein: in muscles, tendons, ligaments for tensile strength & in skin/bones to prevent tearing/fractures
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Spider silk function
produced by spiders for webs - can be extended & are very resistant to breaking
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Denaturing proteins
2 main ways: exposing protein to high temp. & changing the pH of the surrounding solution - can influence functionality
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Temperature effect on proteins: example
when proteins in egg white lose conformation, the interaction between certain amino acids will be changed so the quaternary & tertiary structures (sometimes secondary) are irreversibly changed
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Effect of temp. in general
results in denatured proteins losing form & function, peptide bonds holding adjacent amino acids d o not break
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High fevers danger
temperatures above 40˚C cause proteins to denature & enzymes don't function properly
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Exceptions
Certain enzymes that break down RNA & prion proteins are extremely stable & require long periods of high temperatures (>100˚C) before denaturation
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pH effect on proteins
strong alkaline or acidic solutions can break bonds between non-adjacent amino acids or between polypeptide chains of quaternary proteins - protein denatures & loses functionality
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Other cards in this set

Card 2

Front

Polypeptides

Back

amino acids linked by condensation reactions, nr. of peptides is the polypeptide (aka protein)

Card 3

Front

Basic unit of polypeptides

Back

Preview of the front of card 3

Card 4

Front

Dipeptide

Back

Preview of the front of card 4

Card 5

Front

H2O during condensation

Back

Preview of the front of card 5
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