ACTIVITYGetting to Know the

DNA and RNA Structure

GUIDE QUESTIONSQ1. What are the components of the DNA and RNA molecule?

Fill in the comparison table below.Basis of Comparison DNA RNA

1. Number of Strands 2 1

2. Location in the cell nucleus cytoplasm

3. Type of sugar deoxyribose ribose

4. Nitrogenous base pair A,T,C,G A,U,C,G

ANSWER: SugarPhosphate GroupNitrogenous Base

GUIDE QUESTIONSQ2. What is the structural difference between DNA and RNA?

ANSWER: DNA and RNA are different in the following: a. DNA is double stranded while RNA is single-

stranded. b. The sugar in DNA is deoxyribose while that in RNA is ribose.

c. The nitrogen bases in DNA are adenine (A), guanine (G), thymine (T) and cytosine (C). In RNA are adenine, guanine, cytosine and uracil.

GUIDE QUESTIONSQ3. What nitrogenous base is found in RNA but not in DNA?

ANSWER:

Uracil

DNA(DEOXYRIBONUCLEIC ACID)

- is the main component of chromosomes (packaged form of the DNA)

DNA(DEOXYRIBONUCLEIC ACID)

- is the material that transfers genetic characteristics in all life forms

Where is DNA

found?

DNA STRUCTURE- has three main components:

1. deoxyribose (a pentose sugar)2. base (there are four different ones)3. phosphate

DNA STRUCTURE

nucleotide- formed by the condensation of a pentose sugar, phosphate and one of the 4 bases

DNA STRUCTURENucleotides are linked together by covalent bonds called phosphodiester linkage

DNA STRUCTURE -are divided into two groups:Pyrimidines (are single ring bases.)

Nitrogenous Bases:

C

C

C

C

N

N

O

N

DNA STRUCTURE -are divided into two groups:Pyrimidines (made of one 6 member ring)

ThymineCytosine

Nitrogenous Bases:

C

C

C

C

N

N

O

N

cytosine

C

C

C

C

N

N

O

O

thymine

C

DNA STRUCTURE -are divided into two groups:Purines (made of a 6 member ring, fused

to a 5 member ring; double ring bases)

Nitrogenous Bases:

CC

CC

N

N

N

N

N

C

DNA STRUCTURE -are divided into two groups:Purines (made of a 6 member ring, fused

to a 5 member ring; double ring bases) AdenineGuanine

Nitrogenous Bases:

C

C

C

C

N

N

N

Adenine N

N

C

C

C

C

C

N

NO

N

Guanine N

N

C

• Adenine and Thymine always join together because they form two H bonds with each other

A T• Cytosine and Guanine always join together because they form three H bonds with each other

C G

CHARGRAFF’S RULE

Antiparallel StrandsThe strands run opposite of each other.

The 5’ end always has the phosphate attached.

5’

3’

3’

5’

DNA-is a very long polymer that is double helix with about 10 nucleotide pairs per helical turn

James D. Watson and Francis Crick, co-originators of the double-helix model.

One Strand of DNA

• The backbone of the molecule is alternating phosphates and deoxyribose sugar

• The teeth are nitrogenous bases.

phosphate

deoxyribose

bases

One Strand of DNA

• One strand of DNA is a polymer of nucleotides.

• One strand of DNA has many millions of nucleotides.

nucleotide

Two Strand of DNA

22

• Remember, DNA has two strands that fit together something like a zipper.

• The teeth are the nitrogenous bases but why do they stick together?

HYDROGEN BONDS

C

C

C

C

N

N

O

N

C

C C

C

N NO

N

N

N C

• The bases attract each other because of hydrogen bonds.

• Hydrogen bonds are weak but there are millions and millions of them in a single molecule of DNA.

• The bonds between cytosine and guanine are shown here with dotted lines

DNA by the Numbers

• Each cell has about 2 m of DNA.

• The average human has 75 trillion cells.

• The average human has enough DNA to go from the earth to the sun more than 400 times.

• DNA has a diameter of only 0.000000002 m.

The earth is 150 billion mor 93 million miles from the sun.

What does DNA do?

DNA stores an organism's genetic information and controls the production of proteins and is thus responsible for the biochemistry of an organism.

26

THE CENTRAL DOGMA OF MOLECULAR BIOLOGY

REPLICATIONWhere does

REPLICATION happen?Inside the Nucleus

REPLICATIONWhen does

REPLICATION occur?

occurs during S phase of the

cell cycle.

DNA REPLICATION--- is the process of producing two identical replicas from one original DNA molecule that occurs in all living organisms. --- is the basis for biological inheritance.

DNA REPLICATION--- is a semi conservative

means that each daughter DNA consists of half parental DNA and half of new DNA

2 old strands

2 new strands

SEMICONSERVATIVEand

SEMIDISCONTINOUS

5’

REPLICATION• DNA double helix unwinds

Helicase is the enzyme that splits the two strands. The structure that is created is known as "Replication Fork".

REPLICATION• DNA now single-stranded

Single-Strand DNA Binding Proteins (SSB) for work to bind individuals strands in a DNA double stranded helix and aid the helicases in opening it up into single strands. They are particularly useful in stabilizing the unwound single-stranded formation.

REPLICATION• New DNA strand forms using complementary base

pairing (A-T, C-G)

Example of DNA Replication

5’ TAC CGG AAT GCA ATG CAT ATG 3’ OLD3’ ATG GCC TTA CGT TAC GTA TAC 5’ OLD

5’ TAC CGG AAT GCA ATG CAT ATG 3’ OLD3’ ATG GCC TTA CGT TAC GTA TAC 5’ NEW

5’ TAC CGG AAT GCA ATG CAT ATG 3’ NEW3’ ATG GCC TTA CGT TAC GTA TAC 5’ OLD

REPLICATION• Used to prepare DNA for cell division• Whole genome copied/replicated

REPLICATIONThe following is the base sequence

on one strand of a DNA molecule. If replicated, write the complimentary strands.

1. A A T G C C A G T G G T2. C C T G A C T A A T C G

3. G G A C T G A T T C G G

4. T G G C C T A T A T C C5. G T C A C T G C C G G A

RNA(RIBONUCLEIC ACID)

- Usually one strand

RNA(RIBONUCLEIC ACID)

- The sugar is ribose

RNA(RIBONUCLEIC ACID)

- Contains uracil (U) instead of thymine (T)

RNA(RIBONUCLEIC ACID)

- can both store information and catalyze chemical reactions.

- is used in protein synthesis

TYPES OF RNA(RIBONUCLEIC ACID)

1. messenger RNA (mRNA)-brings information from the DNA in the nucleus to the cytoplasm(cytosol).

2. ribosomal RNA (rRNA)-holds tightly to the mRNA and use its information to assemble amino acids.

TYPES OF RNA(RIBONUCLEIC ACID)

3. transfer RNA (tRNA)-attaches the correct amino acid to the protein chain that is being synthesized in the ribosome

TRANSCRIPTION-is the process by which genetic information from DNA is transferred into RNA. DNA sequence is enzymatically copied by messenger RNA (mRNA) to produce a complementary nucleotide transfer RNA (tRNA) strand.-synthesis of mRNA from a DNA template

TRANSCRIPTION-only one strand of DNA, the antisense strand or template strand, is used to make mRNA

sense strand – is the non transcribed strand

-mRNA is complementary to the antisense strand

Protein Synthesis Transcription

Transcription process•RNA polymerase attaches to DNA at a special sequence that serves as a

“start signal”.•The DNA strands are separated and one strand serves as a template.•The RNA bases attach to the complementary DNA template, thus synthesizing mRNA.

Protein Synthesis: Transcription

•The RNA polymerase recognizes a termination site on the DNA molecule and releases the new mRNA molecule.(mRNA leaves the nucleus and travels to the ribosome in the cytoplasm.)

Protein Synthesis: Transcription

DNA

Cytoplasm

Nucleus

Eukaryotic Transcription

ExportG AAAAAA

RNA

Transcription

Nuclear pores

G AAAAAA

RNAProcessing

mRNA

TRANSCRIPTIONWhere does

TRANSCRIPTION happen?

Inside the Nucleus

http://novella.mhhe.com/sites/0070070017/student_view0/biology_1/chapter_17/mrna_synthesis__transcription___quiz_2_.html

TRANSLATION-process of converting information in mRNA into a sequence of amino acids (polypeptide chain) in a protein-mRNA is in ribosome-Each combination of 3 nucleotides on mRNA is called a codon or three-letter code word. -Each codon specifies a particular amino acid that is to be placed in the polypeptide chain (protein).

TRANSLATION

SUG

AR

-PHO

SPHATE B

AC

KB

ON

E

B A

S E S

H

P OO

HO

O

O

CH2NH2N

NH

N

N

HOH

P

O

O

HO

O

O

CH2

NH2

N

N

N

N

H

P

O

OH

HO

O

O

CH2

NH2

N

N

N

N

O

A Codon

Guanine

Adenine

Adenine

Arginine

TRANSLATION-tRNA brings amino acids to mRNA in the ribosome

TRANSLATION AUG (methionine) serves as the “initiator”

codon, which starts the synthesis of a protein

UAA, UAG, and UGA are stop codons, which signify the end of a polypeptide chain (protein).

THE GENETIC CODE

Ribosomes• 2 subunits, separate in cytoplasm until

they join to begin translation• Large• Small

• Contain 3 binding sites• E• P• A

EP A

Large subunit

Peptidyl-tRNA binding site

Aminoacyl-tRNA binding site

mRNA

5’

Exit site

Small subunit

3’

TRANSLATION

AERibosome P

PheLeu

Met

SerGly

Polypeptide

Arg

Aminoacyl tRNA

UCUCCAGAG...CU-AUG--UUC--CUU--AGU--GGU--AGA--GCU--GUA--UGA-AT GCA...TAAAAAA5’mRNA

3’

TRANSLATION

AERibosome P

CCA

Arg

UCU

PheLeu

Met

SerGly

Polypeptide

GAG...CU-AUG--UUC--CUU--AGU--GGU--AGA--GCU--GUA--UGA-AT GCA...TAAAAAA5’mRNA

3’

TRANSLATION

AERibosome P

Aminoacyl tRNA

CGA

Ala

CCA

Arg

UCU

PheLeu

Met

SerGly

Polypeptide

GAG...CU-AUG--UUC--CUU--AGU--GGU--AGA--GCU--GUA--UGA-AT GCA...TAAAAAA5’mRNA

3’

TRANSLATION

AERibosome PCCA

Arg

UCU

PheLeu

Met

SerGly

Polypeptide

CGA

Ala

GAG...CU-AUG--UUC--CUU--AGU--GGU--AGA--GCU--GUA--UGA-AT GCA...TAAAAAA5’mRNA

3’

TRANSLATION

EXERCISESDetermine the protein formed by the following old DNA strand:

CCCATGGAGCGAGAGTTACCGGGTTAGAGGCAC

new strand:

mRNA:

tRNA:Protein (Amino Acids):

EXERCISESDetermine the protein formed by the following old DNA strand:

AGCATGTGCTACTAGCCGGTGAGC

new strand:

mRNA:

tRNA:

PROTEIN (Amino Acids):

EXERCISESDetermine the protein formed by the following NEW DNA strand:

TGCCGCCAGTCGCTCGGG

a. normal

b. If in the process of transcription, all of the purine, GUANINE is changed to cytosinec. If during transcription, all thymine bases are deleted or not read by the mRNA. d. If all cytosine will be substituted by adenine.