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The sequence of codons on the mRNA is used to generate a specific sequence of amino acids, forming a polypeptide. It takes place on a ribosome and involved tRNA. Each ribosome is made of 2 subunits:
the larger subunit has 2 sited for the attachment of tRNA molecules, so 2 tRNA molecules are associated with a ribosomes at any one time.
the smaller subunit binds to the mRNA.
Ribosome acts as a framework, moving along the mRNA & holding the codon-anticodon compels together, until the 2 amino acids attached to adjacent tRNA molecules bind. The ribosome moves along the mRNA adding 1 amino acid at a time until the polypeptide chain is assembled.
Initiation - ribosome attaches to a 'start' codon at one end of the molecule.
Elongation - the 2 amino acids are sufficiently close for a ribosomal enzyme to catalyse the formation go a peptide bond between them.
Termnation - the sequence repeats until a 'stop' codon is reached.
Usually several ribosomes bind to s single mRNA strand, each reading the coded information at the same time. This is called a polysome. Each ribosome produces a polypeptide, so several are made at once.

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DNA doesn't leave the nucleus. Transcription is the process where part of the DNA, the gene, acts as a template for the production of mRNA which carries info needed for synthesis out of the nucleus and to the cytoplasm. Ribosomes in the cytoplasm proved a suitable surface for the attachment of mRNA & the assembly of protein. This is the sequence of events:
DNA helicase breaks down hydrogen bonds..(see DNA replication)
RNA polymerase binds to the template strand of DNA at the beginning of the sequence to be copied.
Free RNA nucleotides align opposite the template strand, based on the complementary relationship between bases in DNA & the free nucleotides. E.g a nucleotide containing cytosine aligns opposite guanine nucleotide in DNA etc.
RNA polymerase moves along the DNA forming sugar-phosphate bonds that add RNA nucleotides, one at a rime to the growing RNA strand. This results in the synthesis of a molecule go mRNA alongside the unwound portion of DNA. Behind the RNA polymerase, the DNA strands rewind to reform the double helix.
The RNA polymerase separates from the template strand when it reaches a 'stop' signal. The production of the transcript in complete & newly formed RNA detaches from the DNA.

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The stages of protein synthesis:
Transcription: one strand of DNA acts as a template for the production of mRNA, a complementary section of the part of the DNA sequence. This occurs in the nucleus.
Translation: the mRNA acts as a template for the complementary tRNA molecules attach, and the amino acids they carry are linked to form a polypeptide. This occurs on ribosomes in the cytoplasm.

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DNA contains information for making polypeptides, an RNA version of the code is made first from the DNA. In prokaryotes, the RNA is mRNA & directs the synthesis of polypeptide. In eukaryotes the RNA is processed before being used for synthesis.
In eukaryotes, the initial RNA of the code is much longer than the final mRNA & contains sequences of bases that need to be removed. This RNA is called pre-messanger RNA(pre-mRNA) & the sequences that are removed are called introns. They aren't translated into proteins. The introns are cut out of the pre-mRNA using endonuclease & the sequences left are axons, which are joined together and spliced, with ligases.

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The genetic code is a triplet code. It consists of 64 triplets of nucleotides. These triplets are called codons, each codon encodes for 1 of 20 amino acids used in the synthesis of proteins. Most of the amino acids are being encoded by more than 1 codon. These codes are universal for amino acids in all organisms. The genetic code is degenerate by characteristics, this means that most amino acids have more than 1 triplet code/codon. The degenerate nature of the genetic code protects organisms against mutation. The code is non-overlapping: each base occurs in only 1 triplet.

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Initially there were 3 possible mechanisms of DNA replication.
Conservative replication, where the parental double helix remains intact I.e is conserved & a whole new double helix is made.
Semi-conservative replication, in which the parental double helix separates into 2 strands, each of which acts as a temple for synthesis of a new strand. Half the parental material is 'conserved'. Free nucleotides would form the 2nd strand.
Dispersive replication, in which the 2 new double helixes contain fragments from both strands of the parental double helix.
When Watson & Crick built their model of DNA, they realised that complementary base pairs implied that if 2 strands were separated, they would each make another complementary strand. Two new identical molecules would form, each with one old strand & one newly synthesised strand; semi-conservative replication.

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Genetic information coded in the sequence of bases in the DNA, in thousands of sections along its length, called genes. The base sequence determines which proteins are made & it determines which reactions take place in an organism(because enzymes are proteins). If 1 bases coded for 1 amino acid, only 4 could be coded for. If 2 bases coded for 1 amino acid, only 16 could be coded for. If 3 bases coded for 1 amino acid, 64 amino acids could be coded for.

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They grew the bacterium Escherichia coli(E. coli), for several generations in different isotopies of Nitrogen - ¹⁵N(heavy nitrogen). The bacteria incorporated the ¹⁵N into their nucleotides & then into their DNA, that eventually contained only ¹⁵N. The bacteria was extracted & centrifuged it. The DNA settled at a low point in the tube because the 15N made it heavy. The 15N was washed then transferred to a medium containing a lighter isotope of nitrogen, 14N & divided again. Washing it prevented any 15N incorporating into any new strands.

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Chromosomes make copies of themselves, so each daughter receives exact copies of the genetic information.
Helicase - Temporarily removes the helix shape. Helicase will disrupt the hydrogen bond between the bases, separating(unzipping) the DNA.
Primase - It attaches a primer(RNA primer) which will be ~10 bases long & allows DNA to attach & begin to synthesise.
DNA polymerase - Attaches to the ends of the primer, works on a base by base process matching up each & synthesising a strand of DNA which is complementary.
DNA ligase - This attaches or re-forms the sugar backbone of sugar & phosphate

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DNA is in the nucleus of eukaryotes & loose in the cytoplasm of prokaryotes. Small molecules of DNA occur in chloroplasts, mitochondria & some viruses.
Replication - DNA comprises 2 contemporary strands, the base sequence of 1 strand determining the base sequences of the others. If 2 strands of double helix are separated, 2 identical double helixes can be formed, as each parent strand acts as a template for the synthesis of a new complementary strand.
Protein synthesis - the sequence of bases represent the information carried in DNA & determines the sequence of amino acids in proteins.

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DNA & RNA have 4 bases, 3 are the same(ACG)

All have pentose sugar

All contain phosphate

ATP & RNA have ribose sugar - DNA has deoxyribose

RNA has uracil instead of thymine

ATP only has adenine

DNA self-replicates

Only 1 type of DNA & ATP - 3 types of RNA

Both DNA & RNA are involved in protein synthesis - ATPs function is in energy respiration(releases energy when phosphate bond is hydrolysed)

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It's a stable molecule & its information content passes essentially unchanged from generation to generation. It is a very large molecule & carries a large amount of genetic information. The 2 strands are able to separate, as they are held together by hydrogen bonds. As the base pairs are on the inside of the double helix, within the deoxyribose-phosphate backbones, the genetic information is protected.

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RNA is a single stranded polynucleotide, contains the pentose sugar ribose & contains the purine bases adenine & guanine & the pyrimidine bases cytosine & uracil. 3 types of RNA are involved in protein synthesis:
1. Messenger RNA(mRNA) - long, single-stranded molecule. Synthesised in the nucleus & carries the genetic code from the DNA to the ribosomes in the cytoplasm. Different mRNA molecules have different lengths, related to genes from which they are synthesised.
2. Ribosomal RNA(rRNA) -found in the cytoplasm & comprises large, complex molecules. Ribosomes are made of rRNA & protein. They are the site of translation of the genetic code & protein.
3. Transfer RNA(tRNA) - small, single-stranded molecule, which folds so that in places, there are base sequences forming complimentary pairs. Its shape is described as a cloverleaf. The 3' end of the molecule has the sequence C-C-A, when the specific amino acid the molecule carries is attached. It also carries 3 bases called the anticodon. tRNA transports specific amino acids to the ribosomes in protein synthesis.

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Composed of 2 polynucleotide strands would around each other in a double helix

pentose sugar in the nucleotide is deoxyribose

4 organic bases in DNA: two purines(adenine & guanine) two pyrimidines(cytosine & thymine)

'backbone' is formed by the deoxyribose sugar and phosphate groups

bases of 2 strands face each other, pointing inwards. Adenine opposite thymine & guanine opposite cytosine. Hydrogen bonds join the bases & form complimentary pairs, these bonds maintain the shape of the double helix

A DNA molecule is very long, think& tightly coiled within the chromosome

nucleotides in 1 strand are arranged in the opposite direction from those in the complimentary strand. The strands are antiparallel(parallel but facing opposite directions)

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Metabolic processes - to build large, complex molecules from smaller, simpler ones(DNA synthesis from nucleotides)

Active transport - to change the shape of carrier proteins in membranes to allow molecules/ions to move against a conc. gradient

Movement - muscle contractions

Nerve transmission - sodium-potassium pumps actively transport sodium & potassium across the axon membrane

Secretion - packaging & transporting of secretory products in vesicles

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Advantages of having ATP as an intermediate in providing energy compared to glucose directly:

hydrolysis of ATP to ADP involves a single reaction that releases energy immediately, glucose takes longer to break down

only one enzyme is needed to release energy from ATP, many are needed for glucose

ATP releases energy in small amounts, when its needed. Glucose contains large amounts of energy which is released all at once

ATP provides a common source of energy for many different chemical reactions, increasing efficiency & control by the cell

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Universal energy currency in cells because it is involved when energy changes happen. ATP is synthesised when energy is made available(mitochondria) & broken down when energy is needed(muscle contraction). ATP is made up of adenine & three phosphate groups(triphosphate).

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In biological systems, the chemical energy changes because chemical bonds need to be broken for reactions to happen. Heterotrophic organisms(animals) derive their chemical energy from food & autotrophic organisms(green plants) derive their energy from sunlight which is converted to chemical energy during photosynthesis.

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Nucleic acids are polymers(polynucleotides) made up of monomers called nucleotides. There are 3 components combined by condensation reactions:

a phosphate group

a pentose sugar; ribose in RNA & deoxyribose in DNA

an organic base(nitrogenous base)

There are 2 groups of organic bases:
pyrimidine bases: thymine, cytosine & uracil
purine bases: adenine & guanine