The blueprint of life; from DNA to Protein

Bio 261Medgar 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

Figure 16.7a, c

C

T

A

A

T

CG

GC

A

C G

AT

AT

A T

TA

C

TA

0.34 nm

3.4 nm

(a) Key features of DNA structure

G

1 nm

G

(c) Space-filling model

T

O

–O O

OH

O

–OO

O

H2C

O

–OO

O

H2C

O

–OO

O

OH

O

O

OT A

C

GC

A T

O

O

O

CH2

OO–

OO

CH2

CH2

CH2

5 end

Hydrogen bond3 end

3 end

G

P

P

P

P

O

OH

O–

OO

O

P

P

O–

OO

O

P

O–

OO

O

P

(b) Partial chemical structure

H2C

5 endFigure 16.7b

O

N H O CH3

N

N

O

N

N

N

N H

Sugar

Sugar

Adenine (A) Thymine (T)

N

N

N

N

Sugar

O H N

H

NH

N OH

H

N

Sugar

Guanine (G) Cytosine (C)Figure 16.8

H

DNA

The Components and Structure of DNADNA 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.

Figure 17.5

Second mRNA baseU C A G

U

C

A

G

UUUUUCUUAUUG

CUUCUCCUACUG

AUUAUCAUAAUG

GUUGUCGUAGUG

Met orstart

Phe

Leu

Leu

lle

Val

UCUUCCUCAUCG

CCUCCCCCACCG

ACUACCACAACG

GCUGCCGCAGCG

Ser

Pro

Thr

Ala

UAUUAC

UGUUGC

Tyr Cys

CAUCACCAACAG

CGUCGCCGACGG

AAUAACAAAAAG

AGUAGCAGAAGG

GAUGACGAAGAG

GGUGGCGGAGGG

UGGUAAUAG Stop

Stop UGA StopTrp

His

Gln

Asn

Lys

Asp

Arg

Ser

Arg

Gly

U

CA

GUCAG

UCAG

UCAG

Fir

st m

RN

A b

ase

(5

end

)

Th

ird

mR

NA

bas

e (3

en

d)

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

CCACGCUUAA

GACACCU*

GC

* *G U G U *CU

* G AGGU**A

*A

A GUC

AGACC*

C G A GA G G

G*

*GA

CUC*AUUUAGGCG5

Amino acidattachment site

Hydrogenbonds

Anticodon

A

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