biology (Protein synthesis)

• DNA and RNA both carry information.
• DNA holds genetic information, whereas RNA transfers this genetic information from DNA to ribosomes made of RNA and proteins.
• Both deoxyribonucleic and ribonucleic acid are polymers of nucleotides.
• Nucleotides consist of pentose which is a 5 carbon sugar, a nitrogen containing organic base and a phosphate group.
• The components of a DNA nucleotide are deoxyribose, a phosphate group and one of the organic bases adenine, cytosine, guanine or thymine.
• Adenine and guanine both have a double ring structure and are classified as purine bases.
• Substitution is when 1 or more nucleotides are substituted by another in the DNA strand.
• Missense is a mutation resulting in a different amino acid being coded for hence changing the polypeptide chain.
• Mutations are a result of substitution, insertion, and deletion of nucleotides in the DNA strand.
• Nonsense is a mutation resulting in a stop codon hence no polypeptide chain will be formed.
• Insertion is when 1 or more nucleotides are inserted into the DNA strand.
• Silent is a mutation resulting in a different codon however it still codes for the same amino acid meaning the polypeptide chain produced is the same.
• Deletion is when 1 or more nucleotides are deleted in the DNA strand.
• The components of an RNA nucleotide are ribose, a phosphate group and one of the organic bases adenine, cytosine, guanine or uracil.
• Thymine, uracil and cytosine all have a single ring structure and are classified as pyrimidines.
• Nucleotides join together by phosphodiester bonds formed in condensation reactions.
• A double helix composed of two polynucleotides joined together by hydrogen bonds between complementary bases is the structure of DNA.
• In DNA, the 2 strands lie antiparallel and complementary base pairing takes place between the 5’ to 3’ strand and the 3’ to 5’ strand.
• A purine always joins to a pyrimidine base.
• Depending on the bases, a different number of hydrogen bonds are formed.
• Adenine and Thymine join together by 2 hydrogen bonds.
• Cytosine and guanine join together by 3 hydrogen bonds.
• Nucleotides are joined together by phosphodiester bonds.
• RNA is a relatively short polynucleotide chain.
• An RNA nucleotide consists of ribose instead of deoxyribose, a phosphate group and one of the organic bases adenine, cytosine, guanine and uracil (instead of thymine).
• DNA replication ensures genetic continuity between generations of cells meaning that genetic information is passed on from one generation from the next.
• DNA replication occurs during the S phase of the cell cycle.
• The steps of semi-conservative replication of DNA are as following: The double helix unwinds and the hydrogen bonds between the complementary bases break using DNA helicase thus separating the two strands of DNA.
• One of the strands is used as the template and complementary base pairing occurs between the template strand and free nucleotides.
• Adjacent nucleotides are joined by phosphodiester bonds formed in condensation reactions using DNA polymerase DNA polymerase only works in the 5’ to 3’ direction.
• A gene mutation occurs when the base sequence of DNA is altered.
• Translation: During translation amino acids join together to form a polypeptide chain.
• This process is repeated thus leading to the formation of a polypeptide chain until a stop codon is reached on mRNA and ends the process of protein synthesis.
• One of the DNA strands is used as a template to make the mRNA molecule, this is called the template or transcribed strand.
• The hydrogen bonds between the complementary bases break and the DNA uncoils, separating the two strands, this is done by DNA helicase.
• The amino acids attached to the tRNA molecules join by a peptide bond and then tRNA molecules detach themselves from the amino acids, leaving them behind.
• In eukaryotic cells, the RNA molecule formed from transcription is called the primary transcript.
• Free nucleotides bind to the exposed bases via complementary base pairing until a stop codon is reached.
• mRNA attaches to a subunit of a ribosome at the start codon.
• If the DNA sequence is altered, this change is replicated in the mRNA chain and thus can result in an altered polypeptide chain.