Biological Molecules - Proteins Flashcards by Sana Ahmed

Define Amino Acid

An organic compound - contains both an amino group and a carboxyl group
Monomer of protein molecules

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Define Amino Group

NH2
Functional group in amino acids
1 atom nitrogen attached covalently to 2 atoms of hydrogen - leaves a lone valence e- on the nitrogen which is available for bonding to another atom.

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Define Carboxylic acid Group

COOH
Functional group in amino acids
1 carbon atom covalently bonded to 2 oxygen atoms. 1 oxygen atom covalently bonded to hydrogen atom. 1 valence e- on carbon available for bonding to another atom to carboxyl group can form part of larger molecule.

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Collagen

Most common Structural FIBROUS protein found in:
- connective tissue
- bones
- skin
- cartilage

extremely strong - fibres have tensile strength COMPARABLE TO STEEL
3 polypeptide chains - each up to 1000 amino acids long
repeating sequences of glycine w two other amino acids
3 alpha helixes arranged in a TRIPLE HELIX - held together by many hydrogen bonds
Collagen molecules found in fibrils held together to form collagen fibres
Collagen fibres combined w bone tissue

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Condensation

Chemical reaction where 2 molecules joined together by means of covalent bond to form LARGER molecule - at the same time a WATER MOLECULE is RELEASED.

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Dipeptide

Molecule consisting of 2 or more amino acids joined by PEPTIDE bond.

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Disulphide bridge

between 2 sulphur atoms
forms during cross-linking of the amino acids during protein synthesis
Disulphide bonds can be broken by a REDUCING AGENT

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Fibrous Protein

Protein w relatively long + thin structure
INSOLUBLE in water
metabolically INACTIVE
often has a STRUCTURAL role

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Globular Protein

have relatively SPHERICAL molecules
SOLUBLE in water
often have METABOLIC roles in organisms

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Haemoglobin

GLOBULAR Protein which carries oxygen in RBCs - a conjugated protein asw

4 polypeptide chains held together by DISULPHIDE BONDS - 574 amino acids in total
Each chain arranged around iron-containing haem group.
Iron enables haemoglobin to bind to and release O2 molecules.
Arrangement of the polypeptide chains determine how easily oxygen binds/is released.

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Hydrogen Bond

WEAK bond formed when partially positively charged groups come close to partially negatively charged groups.
Seen in water molecules + the secondary and tertiary structure of proteins.
form btwn amino acids w Strongly Polar R groups. Individually weak, collectively strong.

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Hydrolysis

Reaction in which molecule broken down into 2 SMALLER molecules by the ADDITION of a WATER MOLECULE + the BREAKING of a COVALENT bond.

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Hydrophobic

Water-repelling

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Hydrophilic

Water-loving(dissolve in water) - usually polar

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Ionic Bond

Attraction btwn opp charged molecules
Form btwn R groups which have IONISED AMINE AND CARBOXYLIC ACID groups - asparagine + aspartic acid
Easily broken by pH changes
Stronger than hydrogen bonds, weaker than disulphide bridge

hydrogen bond < ionic bond < disulphide bridge

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Peptide

Molecule consisting of small num of amino acids which are bonded together by PEPTIDE bonds

Peptide Bond

Covalent bond which is formed when amino acids joined in a CONDENSATION reaction

Polypeptide

Polymer consisting of many amino acid monomers which are covalently bonded together

Primary structure

The sequence of amino acids found in a protein molecule/polypeptide chain

Protein

Polymer consisting of many amino acid monomers covalently bonded together

Quaternary Structure

Protein Structure where protein consists of MORE THAN ONE polypeptide chain
e.g. Haemoglobin + Insulin

R-group

Side chain of amino acid
Structure of R group decides amino acid special properties

Secondary Structure

Coiling/folding part of the protein due to formation of hydrogen bonds.
Alpha Helix
Beta-pleated Sheets

Tertiary Structure

Overall 3D shape of the protein molecule in WATER.
Held together by bonds between R groups.
Result of interaction btwn parts of the protein: hydrgoen bonding, disulphide bridges, ionic bonds + hydrophobic interactions when in water/a cell.

how many naturally occurring types of amino acids are there?

20 diff types

What elements make up proteins?

Carbon, Hydrogen, Oxygen, Nitrogen(some contain Sulphur)

What are the functions of proteins?

- Enzymes - Hormones - Structural Proteins - Haemoglobin - binds to oxygen - Antibodies

What is the structure of an amino acid?

All amino acids have same basic structure. Central carbon atom which forms bond w 1 carboxyl group + another bond w hydrogen group + third bond w amino group + fourth bond w any of a whole range of groups(R groups) H R O | | || N_____C_____C | | | H H O__H Glycine R Group = H ----- formula = CH2NH2COOH Cysteine R Group = CH2__SH

Where does protein synthesis occur?

In ribosomes in the cell

How does a peptide bond form?

In ribosomes: The amino acids are brought closer together and react to form a peptide bond Peptide bonds = V Strong - involve covalent bonds(sharing of electrons) Formation of Peptide bond happens through CONDENSATION REACTION - Hydrogen and Oxygen atoms are released to form a water molecule which is RELEASED

How are proteins formed in plants?

Plants can manufacture the amino acids which they need. Nitrate obtained from soil --> amino acids then bonded to organic groups which are made from products of P/SYN

How are proteins formed in animals?

Animals take in proteins from diet --> preoteins digested into amino acids Essential amino acid = CANNOT be built from materials taken into body can only be obtained from diet - mostly found in MEAT Animals CANNOT STORE EXCESS AMINO ACIDS - amino group makes the amino acids toxic - amino acids are REMOVED THROUGH DEAMINATION in liver.

How do we test for proteins

BIURET Test: used to determine the presence of peptide bonds in the protein Add Sodium Hydroxide and then Copper Sulphate. If test positive: Solution turns from BLUE to Violet/Purple then the Proteins are present. Solution turns from BLUE to PINK then peptides(short chains of amino acid/residues) are present. If test negative: No change - Biuret solution stays BLUE - no protein present

Where do hydrophobic interactions occur in the tertiary structure?

Occur btwn NON-POLAR R Groups of amino acids. Such R groups tend to be clustered in the CENTRE of the protein molecule. these R groups fold away from water - towards inside of protein -- when in cell

Where are the hydrophilic R groups found in proteins

On the OUTSIDE of GLOBULAR PROTEINS attracted to water - these R groups fold towards the water