• Transcription and Translation

From Wiki-Books:
Compare the structure of RNA and DNA
1. The number of strands.
  • DNA has two strands forming a double helix.
  • RNA has one strand.
2. The type of sugar.
  • DNA has a deoxyribose.
  • RNA has a Ribose.
3. The Nucleotides.
  • DNA has A,C,G,T
  • RNA has A,C,G,U, (Uracil replaces Thymine)
Outline DNA transcription in terms of the formation of the RNA strand complimentary to the DNA strand by RNA polymerase.
  • Transcription: The copying of the base sequence of a gene by making an RNA molecule.
  1. The DNA double helix uncoils and the two strands separate.
  2. RNA Polymerase attaches to promoter regions of the DNA strand
  3. RNA polymerase binds free RNA nucleotides to create mRNA that are a copied template of the corresponding DNA strand.
  4. The mRNA separates from the DNA.
  5. The DNA strands reforms into a double helix.
Describe the genetic code in terms of codons composed of triplets and bases. The genetic code is a triplet code- three bases code for one amino acid. A group of three bases is :*called a codon.
Explain the process of translation, leading to polypeptide formation
  1. Before the mRNA strand is translated, it must be processed. A cap and tail are added to the mRNA strand to allow the mRNA strand out of the nucleus.
  2. There are intron and exon segments of the strand. The introns are removed by the introduction of a splicesome. The splicesome pushes out the introns and binds the exons together.
  3. The mRNA then passes through the nuclear pore and enters the cytoplasm.
  4. The two subunits of a ribosome (60s and 40s) lock onto the mRNA at the ribosome-binding site.
  5. Transfer RNA (tRNA) are clover-leafed shaped molecules that have a specific amino acid attached.
  6. Each tRNA also has three bases called the anticodon that binds to the mRNA. The anticodon determines which amino acid the tRNA carries.
  7. The tRNA can only bind to the mRNA in the presence of a ribosome. In each ribosome there are two tRNA binding sites (Aminoacyl tRNA binding site or A site and Peptidinal tRNA binding site or P site) and a tRNA exit site (E site).
  8. The mRNA is divided into groups of three bases each called a codon. The anticodon on the tRNA binds to the complementary codon on the mRNA. In so doing it brings the amino acid into position.
  9. The mRNA is fed between the small and large subunits of the ribosome. The first tRNA molecule with the attached start amino acid, methanine, attaches at the A site and is transferred to the P site. The next tRNA binds to the mRNA and contains an amino acid.
  10. When two tRNA molecules are bound to the mRNA at the ribosome a ribosomal enzyme forms a peptide bond between the two amino acids.
  11. The first tRNA becomes detached from its amino acid and moves off from the ribosome after it slides into the exit site.
  12. The ribosome moves a distance of one codon and a new tRNA binds bringing in another amino acid to be joined to the polypeptide chain.
  13. The first codon translated on any mRNA is always AUG. This is called the initiation codon and it sets the reading frame of the mRNA.
  14. There are also three codons that signal the end of the mRNA and stop translation. They are the stop codons UAG, UAA and UGA.
  15. Several ribosomes may all be translating the same mRNA at the same time. This is called a polysome.
Define the terms degenerate, and universal as they relate to the genetic code
  • Degenerate: Having more than one base triplet to code for one amino acid.
  • Universal: Found in all living organisms.
Discuss the relationship between one gene and one polypeptide
  • Polypeptides are long chains of amino acids.
  • Amino acids must be linked up in a precise sequence to make a polypeptide.
  • Genes store the information needed to make a polypeptide in a coded form.
  • The sequence of bases in a gene codes for the sequence of amino acids in a polypeptide.
  • The information in the gene is decoded during the making of the polypeptide.
  • This process is conducted in two stages known as transcription and translation.

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Biology Guide

Do the activities:
From Gene to Protein: Transcription
From Gene to Protein: Translation

  • Protein Structure:

From Wiki-books:
Explain the four levels of protein structure

Primary structure
  • A linear sequence of amino acids joined by peptide linkages. There are about 20 different amino acids.
Secondary structure
  • α -Helix is maintained by hydrogen bonds. The helix makes up keratin (skin, nails, hair)
  • β -Pleated Sheet flat zig-zag amino acid chain. The sheets make up fibroin (silk)
Both structures are fibrous and form structural proteins
Tertiary structure
  • Folded polypeptide chains into specific shapes. This means that tertiary proteins are globular (hormones, enzmyes, membrane proteins)
Quaternary structure
  • Two or more polypeptide chains joined (e.g. haemoglobin).
Outline the difference between fibrous and globular proteins, with references to two examples of each protein type
Fibrous proteins (such as keratin, collagen)
  • Chain extended
  • Insoluble
  • Resistance to pH/temperature changes
  • Structural material
Globular proteins (such as haemoglobin, amylase)
  • Chain folded
  • Soluble/colloidal
  • Susceptible to pH/temperature changes
  • Compact, rounded molecules

i-Biology 7.5 Proteins

Biology Guide- 7.5

  • Enzymes

From wiki-books:


Define Enzyme and Active Site
  1. Enzyme: Globular proteins used to catalyze chemical reactions.
  2. Active site: The binding site on the surface of an enzyme where catalysis occurs.
Explain enzyme-substrate specificity
  • The active site for an enzyme is very specific in shape, with very precise chemical properties. Active sites match the shape of their substrates. Other molecules do not fit or do not have the same chemical properties. The enzyme is therefore substrate specific. This enzyme is a lock, and the substrate is the key which can open it.
Explain the effects of temperature, pH and substrate concentration on enzyme activity
  • Temperature, pH and substrate concentration all affect the rate at which enzymes catalyse chemical reactions.
Substrate concentration: At low s.c. the enzyme activity is proportional to the substrate concentration, because of random collision between substrate and enzyme. Thus the more substrate the higher the rate. However at a high substrate concentration, at some point all active sites are occupied so raising the substrate concentration has no effect.
Temperature: Enzyme activity increases as temperature increases, often doubling with each 10°C. This is because collision between substrate and active site happen more frequently at higher temperatures, due to fast molecular movement. However at high temperatures enzymes are denatured and stop working. This is because heat causes vibrations inside the enzyme, which break bonds needed to maintain the structure.
pH: There is an optimum at which enzyme activity is fastest ( mostly pH 7), and as pH increases or decreases from its optimum, enzyme activity is reduced. (acids and alkali denature enzymes)
Define Denaturation
  • Denaturation: A structural change in a protein that results in a loss of its biological properties. This can be caused by pH or by temperature.
Explain the use of lactase in the production of lactose free milk

Lactose- The sugar present in milk. Lactose is obtained from Kluveromyces and lactis. Lactose can be converted to glucose and galactose using the enzyme lactase (di-saccarharide). Biotechnology companies culture the yeast and extract the enzyme in order to produce lactose free milk.
  • Advantages: Pectinase makes juice more fluid and easy to separate from pulp.
  • Fructose is widely used in food manufacturing because it is much sweeter than glucose. It is made from starch, usually found in maize. Amylase is needed to break down the starch into glucose.
  • 'Source of Enzyme: Amylase is obtained from fungi.
  • Use: Used to break Starch into glucose, which is then converted into fructose using the enzyme glucose isomerase.
i-Biology Enzymes

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Biology Guide