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🪢 Protein synthesis amd central dogma Created Tags June 13 , 2025 1002 PM Pr ot ein synthesis amd central dogma 1

Questions regarding DNA structure Importance of the ratios of A to T and G to C to the structure of DNA The ratio of AT and CG is approximately 11 as specific complementary pairing occurs between A and T, C and G Hydrogen bonds hold two strands together which contributes towards the stability of the double helix A a purine 2 rings) is paired with a pyramidine 1 ring) which provides the same width of 2nm throughout double helix, contributing towards stability of DNA Structure of DNA that makes it stable as a hereditary material / contribute to its stability Numerous hydrogen bonds that hold the two DNA strands together via complementary base pairings to stabilise the structure of the DNA double helix prevents them from DNA separation DNA has a double helix structure to protect nitrogenous bases from degradation by preventing enzyme access to the bases and more resistant to mutations DNA is double strand and each strand can serve as a template to repair any DNA damage to maintain structure integrity amd can be replicated accurately or one strand can serve as a template for repair if the other has a mutation on it hence there is a backup code Numerous hydrogen bonds hold the two strands together and adjacent nucleotides in each strand in each strand are joined by strong covalent phosphodiester bonds in sugar phosphate backbones to prevent breaking up of DNA nucleotide sequences on the DNA strand, generations of coded information can be passed on to next generation without any loss Base stacking stabalises double helix through hydrophobic interactions between the planar structure of bases Lack of hydroxyl group at carbon 2 of deoxyribose reduces reactivity of DNA Pr ot ein synthesis amd central dogma 2

Hereditary material: Access to DNA is tightly regulated by histone proteins which packs and folds DNA to make it more compact into chromosomes to prevent DNA damage Coded information can be readily utilised as DNA strands are held by weak hydrogen bonds allowing the template strand to separate from non-template strand allowing transcription take place Complementary base pairings between complementary nucleotide sequences on each strands allow faithful transfer of information from DNA to RNA transcription, which will be translated to protein subsequently Describe structure of DNA Molecular level: DNA is a polymer of nucleotides Basic unit of DNA molecule is deoxyribonucleotides Nucleotides consists of a pentose sugar which is deoxyribose , phosphate group and a nitrogenous base Types of nitrogenous bases are adenine, guanine, thymine and cytosine Purines are nitrogenous bases with 2 rings while pyrimidines are nitrogenous bases with 1 ring. Purines are purer and have 2 virginity rings) Purines include Adenine and guanine while pyrimidines include thymine and cytosine Nitrogenous base is joined to carbon 1 of deoxyribose sugar by covalent bond Phosphate group joined to carbon 5 of deoxyribose sugar by phosphodiester bond and they are negatively charged molecule Nucleotides are joined together by phosphodiester bonds to form poly nucleotides, whereby the 3 OH end of a nucleotide joins with the 5 phosphate end of adjacent nucleotide The sugar-phosphate backbone of a strand of polynucleotide is formed by deoxyribose and phosphate and lies on the outside of the molecule with the nitrogen-containing bases on interior Pr ot ein synthesis amd central dogma 3

Each strand of polynucleotide has a 5ʼ end and a 3ʼ end which refers to the phosphate group attached to the 5th carbon of the deoxyribose and OH group attached to the 3rd carbon of deoxyribose respectively DNA in prokaryotes and eukaryotes consists of two strands of polynucleotides and in virus can either be single stranded or double stranded In double stranded DNA, two strands are anti parallel to each other Polynucleotides in dsDNA held together by hydrogen bonds via complementary base pairings Adenine forms two hydrogen bonds with thymine Cytosine forms 3 hydrogen bonds with guanine Double stranded DNA forms a double helix structure with a minor and minor groove Helix is right handed Role and property of DNA Function:store genetic information and pass it on from one generation to the next Property: It can be replicated accurately so that information can be passed down to next generation, ensuring daughter cells have identical copies of DNA as parent cell It is chemically stable to encode information without being easily degraded and passed to next generation without loss of coded information There is backup of code as DNA is double stranded Coded information readily utilised due to weak hydrogen bonds Capable of variation to allow evolutionary changes in a population Questions regarding DNA replication Why are two DNA polymerase needed for replication? Pr ot ein synthesis amd central dogma 4

The double stranded DNA is anti parallel in nature and since DNA polymerase is only synthesised in the 5ʼ to 3ʼ direction, necessary for two polymerase for more efficient replication Prevent degradation of single stranded DNA as efficiency is increased How End replication problem arises and its consequences Occurs during replication or linear DNA Unable to fill gap after last RNA primer at the 5ʼ end is removed at the end of lagging strand as there is no pre-existing 3OH group that DNA polymerase can bind to and elongation occurs in the 5ʼ to 3ʼ direction forming a 3ʼ overhang This results in shortening of daughter strand compared to parental strand,3ʼ end not completely replicated However, since telomeres are non-coding, this ensures vital genetic information not lost with each round of replication If telomeres shorten to critical length, cell will be signalled to stop dividing Pr ot ein synthesis amd central dogma 5

Describe DNA replication Occurs in the nucleus Enzyme helicase binds to the origin of replication and unwind the DNA helix by breaking the hydrogen bonds between complementary bases causing the parental strands to unzip and separate Single stranded binding proteins keep the strands apart so that they can act as the template for DNA synthesis Topoisomerase will relieve overwinding strain ahead of replication bubble by breaking and rejoining DNA strands An enzyme primase synthesis RNA primer which will then be added to each parental strand to provide a free 3 OH group for DNA polymerase iii to recognise and bind to as the 3D conformation of the active site of DNA polymerase is complementary to the 3OH group and hence initial of replication occurs from the 5ʼ to 3ʼ direction This is because DNA polymerase can only add nucleotides to the new strand to a free 3 OH group from a pre-existing strand (in this case the RNA primer) DNA polymerase iii binds to the RNA primer, recruits and attaches free nucleotides to the new strand in a sequence complementary to the parental strand, catalysing phosphodiester bonds between adjacent daughter DNA nucleotides of the newly synthesised strand and it also prof reads as it moved along the template, removing and replacing any incorrect deoxyribonucleotides Base pairing occurs between adenine and thymine, cytosine and guanine DNA polymerase I will hydrolyse the RNA primers and replace it with deoxyribonucleotides It will add nucleotides to the pre-existing 3ʼ OH end of the newly synthesised DNA strand DNA ligase seals the gap by catalysing formation of phosphodiester bond between the 3OH of one nucleotide and 5ʼ phosphate of adjacent nucleotide Pr ot ein synthesis amd central dogma 6

DNA replication is semi conservative as each new dna molecules contains one original parental strand and one newly synthesised strand Only one strand called the leading strand is synthesised continuously the other strand is called lagging strand as it undergoes discon