beetroot experiment

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Why does the colour leak out of cooked Beetroot?

Introduction:

        The purpose of this experiment is to investigate the effect of temperature on membrane structure and highlight experimental and investigative skills.

Background Knowledge:

        Beetroot appears as a dark/red purple colour caused by betalain pigment which is contained within the vacuole of beetroot cells. In order for the betalain to leave the cell, it needs to pass through different membranes, the membrane bounding the vacuole and membrane enclosing the cell. Beetroot cells are quite unstable and will leak out when cut, heated, cooked, or when in contact with air or sunlight. This can also be showed and done by adding detergents and solvents as part of solution with the beetroot. Beta lain pigments are named after “beet” family of plants.

        Plant cells are quite different from other eukaryotic kingdom’s organisms. Their distinctive features are: large central vacuole that maintains the cell's turgid and controls movements of molecules' cytosol and sap, of course chloroplast that contain chlorophyll which is the pigment that allows photosynthesis and more importantly the nucleus which controls the whole activity of the cell, also a wall made up of cellulose and protein deposited by protoplast on the outside of cell membrane. The plasma membrane is the inner layer of protection surrounded by rigid cell wall.        

        The purpose of a cell membrane is to control the transport of substances moving into and out of the cell. The cell membrane is partially permeable due to its thin layer (7-10 nanometres) thick. It consists mostly of lipids and proteins the lipids found in cell membranes are triglycerides, have one molecule of glycerol chemically linked to 3 molecules of fatty acids, the majority being phospholipids.

        

        Biological membranes are bilipid layers. Phospholipids create a spherical three dimensional lipid bilayer shell around the cell. Each of the phospholipids molecules has two parts:

        The circle or head is the negatively charged phosphate group which is has a strong polarity because of sharing of electrons within this part of molecule is not quite even. One end becomes slightly positive and other end is negative. So this makes the phosphate head attract other polar molecule- the water. It is hydrophilic.

        Two tails are the two hydrocarbon chains of phospholipids. The tails of the phospholipids orient towards each other creating a hydrophobic environment. The bilipid layer is semi-permeable, meaning that some molecules are allowed to diffuse freely through membrane. Molecules that can diffuse through the membrane due so at differing rates depending upon their ability to enter the hydrophobic interior of the membrane bilayer.

        

        Diffusion refers to process by which molecules intermingle as a result of kinetic energy of random motion. It is the movement of particles from higher concentration or chemical potential to lower chemical potential. In cell biology, diffusion is often described as a form of passive transport by which substances cross membranes so no energy is expended in movement.

        Lipid bilayers are fluid and individual phospholipids diffuse rapidly throughout the two-dimensional surface of membrane; tail and head. This is known as “fluid mosaic model of biological membrane”. It is called as “mosaic” because it contains proteins and cholesterols, etc.

        Some phospholipids have carbohydrates attached to them called as glycolipids some proteins have carbohydrates attached to them called as glycoprotein. From time to time a given phospholipids will “flip-flop” through the membrane to opposite side but it is uncommon. To do so, it requires the hydrophilic head of phospholipids to pass through the hydrophobic interior of membrane and for the hydrophobic tails to be exposed to the aqueous environment. Some proteins span the membrane, other points only within inner layer(intrinsic protein) and some only within outer layer(extrinsic protein).

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        The molecules of cholesterol embedded in the membrane reduce the fluidity of the cell membrane by preventing the movement of phospholipids because it makes the fatty layer more viscous and more repellent to water. Another way for the cell to control the fluidity of its membrane is to regulate the ratio of saturated to unsaturated hydrocarbon chains of the phospholipids. Saturated hydrocarbons are straight-chains so it fits together and can pack close together tightly and hold the phospholipids to each other. Some are unsaturated fatty acids, so it bent and fit together loosely. The more unsaturated they are, the ...

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