The blueprint of life; from DNA to Protein

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

DNA, the substance of inheritance • 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

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

5 end O OH Hydrogen bond P 3 end –O O OH O A T O CH2 O O P O –O O– O P O H2C O O G C O O CH2 O P O O O –O O– O– O– O P P P O O O H2C O O O O C G O O CH2 O P –O O H2C A T O O CH2 OH 3 end (b) Partial chemical structure 5 end Figure 16.7b

H N O H CH3 N N N N H Sugar N N O Sugar Adenine (A) Thymine (T) H O N H N N N H N Sugar N N N O H Sugar H Figure 16.8 Cytosine (C) Guanine (G)

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.

DNA Double Helix

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 sense strand. It serves as a template for the production of messenger RNA.

Transcription begins when an enzyme called RNA polymerase binds to a special region of the DNA called promoter sequence. Unlike DNA polymerase, RNA polymerase doesn’t need a primer. • RNA polymerase brings free floating RNA nucleotides to the sense strand.

Guanine and cytosine pair up. • But, there is no thymine in RNA. Another base called Uracil pairs up with adenine. • The messenger RNA strand will continue to elongate until it reaches a termination point.

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 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.

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

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

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

The blueprint of life; from DNA to Protein