The blueprint of life; from DNA to Protein Biology 261 Medgar Evers College Prof. Santos

DNA, the substance of inheritance Hereditary information Is the most celebrated molecule of our time Hereditary information Is encoded in the chemical language of DNA and reproduced in all the cells of your body It is the DNA program That directs the development of many different types of traits

(a) Key features of DNA structure (c) Space-filling model Figure 16.7a, c C T A G 0.34 nm 3.4 nm (a) Key features of DNA structure 1 nm (c) Space-filling model

DNA The Components and Structure of DNA DNA is made up of nucleotides. A nucleotide is a monomer of nucleic acids made up of: Deoxyribose – 5-carbon Sugar Phosphate Group Nitrogenous Base

There are four kinds of bases in in DNA: adenine guanine cytosine thymine

Chargaff’s rule Chargaff's Rules Erwin Chargaff discovered that: The percentages of guanine [G] and cytosine [C] bases are almost equal in any sample of DNA. The percentages of adenine [A] and thymine [T] bases are almost equal in any sample of DNA.

There are 2 hydrogen bonds between adenine and thymine and three hydrogen bonds between cytosine and guanine.

DNA to RNA to Protein connection

Protein synthesis 3 steps 1- transcription 2- RNA processing 3- translation

Transcription Copying the genetic code directly from DNA. We make a single strand of messenger RNA. We begin initiation by unwinding the double stranded DNA and copying only one of the strands. The strand that is copied is called the nonsense strand. It serves as a template for the production of messenger RNA.

RNA processing The pre messenger RNA made must be modified before it can leave the nucleus and direct the production of proteins. 3 steps 1- removal of introns 2- addition of cap at 5 end 3- poly A tail at 3 end

The coding regions are called exons and the non-coding regions are called introns. The introns are removed by an enzyme-RNA complex known as the spliceosome. A tail of adenine bases is added to the 3 prime end and a modified guanine nucleotide is added to the 5 prime end.

Once the messenger RNA has been processed, it is ready to leave the nucleus and bind to a ribosome. The mature messenger RNA carries the message from DNA in the forms of codons. A codon is a group of 3 bases that correspond to one of the 20 amino acids.

There are 64 possible codons and only 20 amino acids There are 64 possible codons and only 20 amino acids. There is redundancy with some of the amino acids! The initial codon is AUG or methionine and there are three stop codons, UAA, UGA and UAG.

Figure 17.5 Second mRNA base U C A G UUU UUC UUA UUG CUU CUC CUA CUG AUC AUA AUG GUU GUC GUA GUG Met or start Phe Leu lle Val UCU UCC UCA UCG CCU CCC CCA CCG ACU ACC ACA ACG GCU GCC GCA GCG Ser Pro Thr Ala UAU UAC UGU UGC Tyr Cys CAU CAC CAA CAG CGU CGC CGA CGG AAU AAC AAA AAG AGU AGC AGA AGG GAU GAC GAA GAG GGU GGC GGA GGG UGG UAA UAG Stop UGA Trp His Gln Asn Lys Asp Arg Gly First mRNA base (5 end) Third mRNA base (3 end) Glu

Translation The messenger RNA attaches to the ribosome and the message in the form of codons is “translated” and the appropriate amino acid is put in place. A molecule of RNA called transfer RNA brings along the amino acid. It resembles a four leaf clover. On the top is the amino acid and on the bottom is a sequence known as the anti codon.

3 C A G U * 5 Amino acid attachment site Hydrogen bonds Anticodon

The anticodon pairs up with the codon The anticodon pairs up with the codon. This allows the amino acids to put placed in the correct sequence or order.