Biomolecules — Proteins

Amino Acids:

The basic building blocks of proteins are amino acids. Amino acids are the monomers which form polypeptide and proteins.

Properties of Proteins:

• sensitive to pH and heat
• shape determines function
• enzymes are special group of proteins
• contain H, N, C and S
• made up of amino acids

There are about 20 essential amino acids found in proteins, and they differ in their R group. 

Amino acids join together to form a polypeptide through the process called condensation.

Two amino acids are joined by a peptide bond to form a dipeptide via condensation. Water is formed as a by product. 

The reaction is between an amino group and a carboxyl group. 

Continued condensation leads to the addition of more amino acids and thus resulting in a polypeptide chain.

 

Structure of proteins:

1. Primary structure --> specific linear order which amino acids join to form a polypeptide chain
2. Secondary structure --> regular folding of segments by hydrogen bonds (α-helix and β-pleated sheet)
3. Tertiary structure --> (only for globular proteins) overall shape of polypeptide resulting from interactions* between the R group 
4. Quaternary structure --> association of 2 or more polypeptide chains 

*Bonds that form tertiary structures:

• hydrogen bonds
• ionic bonds
• disulfide bonds
• hydrophobic interaction

Classification of proteins (based on structure):

• Globular --> compact and spherical structure which is soluble
• Fibrous --> long polypeptide chains twisted around each other, forming long fibres that provide tensile strength, insoluble 

Cell Transport

Passive transport (requires no ATP as molecules move along a concentration gradient):

• Simple Diffusion
• Facilitated Diffusion
• Osmosis

Active transport (requires ATP as molecules move against a concentration gradient):

•  Endocytosis
•  Exocytosis
•  Pinocytosis (“drinking”)
•  Phagocytosis

Simple Diffusion

• Net movement of molecules in and out of the cell along a concentration gradient
• Eg. gas exchange during photosynthesis, gas exchange at the alveoli 

Facilitated Diffusion

• Movement of specific molecules down a concentration gradient through specific carrier proteins
• Molecules that move by facilitated diffusion include glucose and amino acids

Osmosis

• Net movement of water molecules from a region of higher water potential to a region of lower water potential, across a partially permeable membrane
• Eg. absorption of water by plant roots

credits to: http://www.biologymad.com/resources/diffusionrevision.pdf

Cell membrane structure

Function of cell membranes:

•      To compartmentalize the cell --> separate different enzymes of different organelles and prevent autolysis
•      Control entry and exit of substances
•      Increases surface area for exchange of substances
•      Cell recognition
•      Cell communication
•      Site of chemical reactions (eg. light reactions of photosynthesis)

Fluid mosaic model

The cell membrane consists of:

• phospholipids --> head is polar while tail is non-polar 
• proteins --> peripheral/integral proteins 
• glycoproteins (consists of carbohydrate chains bound to peripheral proteins and hydrophilic regions of integral proteins) 
• cholesterol --> maintains membrane fluidity

Cell Structure — Animal cell vs Plant cell

Animal Cell structure

Plant Cell structure

credits to: http://www.diffen.com/difference/Animal_Cell_vs_Plant_Cell

Biological Molecules - You Are What You Eat: Crash Course Biology #3

A helpful video on biomolecules!

 ← screengrab from the video!