Proteins, nucleic acid and transport across a membrane

Proteins, nucleic acid and transport across a membrane

What is the structure of an amino acid?

1\. Has an amine group (NH2)

2\. Has a carboxyl group (COOH with double bonded O)

3\. Has an R group (rest of the molecule)

What bonds join together amino acids

Peptide bonds

What is a protein made up of (state all monomers involved)?

Amino acid → dipeptide → polypeptide → protein

What is the primary structure of a protein?

Is the sequence of amino acids held together by covalent peptide bonds

What is the secondary structure of a protein?

The folded 3D structure of the polypeptide- either a-helix or B-sheets held together by hydrogen bonds

What is the tertiary structure?

Other forces (disulphide bridges, ionic and hydrogen bonds) that cause further twisting and folding

What are the bonds present in the tertiary structure of proteins

1\. Disulphide bridges- strong bonds between cysteine

2\. Ionic bonds- weaker than disulfide and formed between carboxyl and amino groups

3\. Hydrogen bonds- numerous and easily broken

What are globular and fibrous proteins?

Globular- compact \n Fibrous- long and can form fibres

State and explain the test for proteins

Add sodium hydroxide in equal measure to the sample. Add Biuret solution (very dilute copper sulphate). Solution will turn lilac if peptide bonds are present

What is the function of enzymes

They increase the rate of reaction by lowering the activation energy of the reaction they catalyse

Describe the structure of an enzyme

They are 3D tertiary structured globular proteins whose shape is determined by the primary sequence of amino acids

Describe the induced-fit model

Enzymes are specific to substates they bind to, forming an enzyme-substate complex. The structure of the enzyme then changes slightly to fit around the substate.

Describe the effect of temperature on RoR

Initially the rate of reaction will increase as the kinetic energy increases, however once the temperature gets too high, the enzyme gets denatured

Describe the effect of pH on RoR

pH affects the enzymes shape as it can disrupt the bonds in the tertiary structure of the enzyme. The optimum pH will depend on the enzyme

Describe the effect of enzyme concentration on RoR

The rate of reaction will increase the higher the concentration of enzymes as there will be more active sites to bind to. This occurs until substrates are the limiting factor

Describe the effect of substate concentration on RoR

The rate of reaction will increase the higher the concentration of substates as there will be more enzyme-substate complexes formed. This occurs until the enzymes are the limiting factor

Describe the effect of concentration of competitive reversible inhibitors

As concentration increases, rate of reaction decreases as the active sites are temporarily blocked by inhibitors so substrates cannot bind to them

Describe the effect of concentration of non-competitive reversible inhibitors

As concentration increases, rate of reaction decreases as the shape of the enzyme (not the active site) is altered by the inhibitors.

What was the original model of how enzyme action occured

Lock and key model

What is the role of DNA and RNA?

DNA holds genetic information and RNA transfers genetic information from DNA to ribosomes

What is the structure of a nucleotide?

There is a phosphate, pentose sugar and a nitrogen containing organic base

What are the 4 bases of DNA?

Adenine, thymine, guanine, cytosine

What are the components of an RNA nucleotide?

1\. Ribose sugar

2\. A phosphate group

3\. A base

How are nucleotides joined together?

They are bonded in condensation reactions forming phosphodiester bonds

Describe the structure of DNA

It is a double helix composed of two polynucleotides joined together by a hydrogen bonds between complementary bases

What is the structure of RNA

It is a relatively short polynucleotide chain

Why is DNA a stable molecule?

1\. It has a phosphodiester backbone which protects the more chemically reactive nitrogen contain ing organic bases

2\. Hydrogen bond form bridges between the phosphodiester uprights. There are 3 bonds between G and C, and 2 bonds between A and T

What is the term used to describe how DNA replicates

Semi-conservatively

Describe the process of semi-conservative replication

2\. DNA helicase, causes the two strands of DNA to separate breaking the hydrogen bonds between the complementary bases.

3\. One of the strands is used as the template and complementary base pairing occurs between the template strand and free nucleotides.

4\. Once activated nucleotides are bound the enzyme DNA polymerase joins them together by forming phosphodiester bonds. The result is that two identical strands of DNA are formed

Describe the structure of the cell membrane

1\. They contain both extrinsic and intrinsic proteins embedded in the phospholipid bilayer.

2\. Attached to some extrinsic proteins are carbohydrates

3\. There are also glycolipids and glycoproteins

What is the name given to the structure of the cell membrane

The fluid mosaic model

Describe simple diffusion through the cell membrane

It is the passive movement of small, non-polar, lipid soluble molecules such as CO2 and O2 down the concentration gradient, which move directly through the phospholipid bilayer

Describe facilitated diffusion in the cell membrane

Occurs through a channel protein in the cell membrane to transport polar molecules, charged and water soluble molecules across the membrane

Describe the process of osmosis within the cell membrane

The diffusion of water molecules from an area of high water potential to an area to low water potential through a partially permeable membrane

Describe the process of active transport

1\. Occurs with the sodium-potassium pump in the ileum.

2\. K+ is actively transported into the cell and Na+ into the bloodstream.

3\. This maintains a low conc of Na+ ions in the epithelial cell

4\. Facilitated diffusion of Na+ ions from ileum to epithelial cell doen a conc gradient, glucose follows by co-transport

5\. Glucose then enters the capillary by facilitated diffusion