Nucleic Acids and Protein Synthesis ppt.pdf

8/11/2019 Nucleic Acids and Protein Synthesis ppt.pdf

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DNA and RNA are

polymersconsistingof repeatingsubunitscallednucleotides,

which aremade ofthreecomponents:

a heterocyclic

nitrogenous basea sugar

phosphate


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A ring that contains elementsother than carbon is called aheterocyclic ring.

The bases found in RNA and DNAcontain two types ofheterocyclic rings: pyrimidine

and purine


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Purine ring Pyrimidine ring


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pyrimidine bases:uracil(U),

thymine(T),cytosine(C)


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Nucleoside is a combination of base and asugar bonded together by N-- glycosidicbond

C# 1 of the sugar is linked to:N in position of 1 of pyrimidine

N in position of 9 of purine


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NUCLEOSIDE

RIBONUCLEOSIDE DEOXYRIBONUCLEOSIDE


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Ribonucleoside could be:

Purine ribonucleoside = purine + ribose

Pyrimidine ribonucleoside = pyrimidine +ribose

Purine ribonucleosideAdenosine = adenine + ribose

Guanosine = guanine a+ ribose

Pyrimidine ribonucleoside

Cytidine = cytosine + ribose

Uridine = uracil + ribose

Thymidine = thymine + ribose


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Deoxyribonucleoside could be:

Purine deoxyribonucleoside = purine +deoxyribose

Pyrimidine deoxyribonucleoside =pyrimidine + deoxyribose

Purine deoxyribonucleoside

Deoxyadenosine = adenine + deoxyribose

Deoxyguanosine = guanine + deoxyribose

Pyrimidine DeoxyribonucleosideDeoxycytidine

Deoxyuridine

Deoxycytidine


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Nucleotides are formed from thecombination of nucleoside with phosphoricacid


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ADENOSINE-5- MONOPHOSPHATE


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NUCLEIC ACID - consists of successivenucleotide units joined together byphosphodiester bond.

The nucleic acid backbone then is asequence of sugar-phosphate groups, whichdiffer only in the sequence of bases

attached to the sugars along the backbone


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A key feature of all nucleic acids - theyhave two distinctive ends: the 5' and 3'ends.

For both DNA (shown above) and RNA,

the 5' end bears a phosphate, and the3' end a hydroxyl group.


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The bases hydrogen bond to each other in a

specific way: A hydrogen bonds to T, and Ghydrogen bonds to C, forming a set ofcomplementary base pairs:


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In the early 1950s,Watson and Crick

determined the truestructure of DNA fromdata and X-ray pictures.

In 1953, Watson and

Crick published a paperthat showed that notonly is the DNAmolecule double-stranded, but the twostrands wrap around

each other forming acoil, or helix. The truestructure of the DNAmolecule is a doublehelix.


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The ladder-likestructure folds inon itself to form adouble helix, with

the bases on theinside and thesugar-phosphatebackbone on the

outside.


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RNAs are usuallysingle stranded, butmany RNA

molecules havesecondarystructure in whichintramolecularloops are formed

by complementarybase pairing. Base pairing in RNA

follows exactly thesame principles as

with DNA the base pairs that

form are A-U and G-C.


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DNA RNA

Sugar -deoxyribose

Bases - A, G, C T

Double stranded

Sugar - ribose

Bases - A, G, C, U

Single stranded


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There are 3 classes of RNA

1.) messenger RNA , mRNA2.) transfer RNA, tRNA

3.) ribosomal RNA, rRNA


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Messenger RNA (mRNA) functions as a carrier ofgenetic information fromthe DNA in the cellnucleus to the site of

protein synthesis in thecytoplasm.

mRNA has a short lifetime(usually less than onehour); it is synthesized as

it is needed, then rapidlydegraded to theconstituent nucleotides


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Ribosomal RNA (rRNA) themain component of ribosomesthat are the site of protein

synthesis.rRNAaccounts for 80-85% of thetotal RNA of the cell.

rRNAaccounts for 65% of aribosomes structure (the

remaining 35% is protein).


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Transfer RNA (tRNA) deliversindividual amino acids to the siteof protein synthesis.

tRNA is specific to one type of aminoacid; cells contain at least onespecific type of tRNA for each of the

20 common amino acids.tRNA is the smallest of the nucleic

acids, with 73-93 nucleotides per

chain.


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tRNA- has 2 segments;

Amino acidattachment

Anticodon loop-three-base sequence

which allows tRNA tobind to mRNA duringprotein synthesis.

(It is complementaryto one of the codonsin mRNA.)


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It reproduces itself

( REPLICATION)It supplies the informationnecessary for the synthesis of

protein in our body includingenzymes ( PROTEIN SYNTHESIS)


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Replication is the process by which anexact copy of DNA is produced

HEREDITY - transmission of geneticinformation from parents to offsprings.

Transmission of hereditary information takesplace in the nucleus. Chromosomes - structure inside the nucleus

which has something to do with heredity.,

The GENES are located in the chromosomes;the genes are section of the DNA.

GENE is a a segment of deoxyribonucleicacid (DNA) carrying the code for a specificpolypeptide.


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Each gene is a section of DNA molecule thatcontains specific sequence of 4 bases namely,A, G, C, and T containing 1000- 2000nucleotides.

The DNA double helix contains thousands ofbases. One strand of DNA may carry manyinheritable genes.

Genetic information is transmitted from onecell to the next, when cell division occurs.The two new cells carry all the informationthat the original cell possessed.


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Two strands of DNA

separate, and eachone serves as thetemplate for theconstruction of itsown complement,

generating new DNAstrands that areexact replicas of theoriginal molecule.

The two daughter

DNA molecules haveexactly the samebase sequences ofthe parent DNA


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Step 2: Synthesis of DNAsegments.

All the kinds of the free DNAnucleotide molecules arepresent in the vicinity.These nucleotidesconstantly move into thearea and try to fitthemselves into the newchain.

While the bases of the newlyarrived nucleotides arebeing hydrogenated to theirpartners, the enzymepolymerase join thenucleotide backbone. At the

end of the process, thereare two double strandedDNA molecule each exactlythe same as the originalone.


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The central dogma of molecular biologystates that genetic information containedin the DNA is transferred to RNA moleculesand then expressed in the structure ofsynthesized proteins.

Genes are segments of DNA that containthe information needed for the synthesis of

proteins. Each protein in the body corresponds to a

DNA gene.


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Th i h fl f i


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There are two steps in the flow of geneticinformation:

transcriptionthe DNA containing the

stored information is in the nucleus of thecell, and protein synthesis occurs in thecytoplasm. The information stored in theDNA must be carried out of the nucleus bymRNA.

The RNA copy of the gene is called the mRNA

translationmRNA serves as a template onwhich amino acids are assembled in thesequence necessary to produce the correct

protein. The code carried by mRNA istranslated into an amino acid sequence bytRNA.


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The copying of information isdone with the help of the

enzyme RNA polymerase, whichcatalyze the synthesis of mRNA


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DNA double helix begins

to unwind at a pointnear the gene that is tobe transcribed.

Ribonucleotideassemble along theunwound DNA strand in

a complimentarysequence.

Ex. Opposite each C onthe DNA, there is G onthe growing mRNA andother complimentarybases follow thepatterns.( A::U, G:::C).


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On the DNA strand,there is always asequence of bases thatthe RNA polymerase

recognizes as aninitiation signal, saying start here

At the end of the gene,

there is a terminationsequence that tells theenzyme, stop thesynthesis.

The newly-synthesized

mRNA strand movesaway from the DNA,which rewinds into thedouble helix.


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TRANSLATION - process by which genetic

information preserved in the DNA andtranscribed into the mRNA is converted tothe language of protein ( amino acidsequence)

Language of DNA Language of ProteinCodon

GCU . . . . . . . . Ala

GUU . . . . . . . . Val

Each base triplet sequence thatrepresents a code word on mRNA moleculesis called a codon


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1.) Ribosomes begins to read the mRNAsequence from the 5` end to the 3` end.

To convert the mRNA into proteinlanguage, tRNA is used to read the mRNAsequence, 3 nucleotides at a time.

GENETIC CODE - dictionary oftranslation Correspondence between the codon and one

amino acid

There are 20 amino acids in protein, but

there are 64 possible combinations of 4 basesinto triplets or codons.


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Most amino acids are represented by more

than one codon (a feature known asdegeneracy).

Three are stop3 signs; 61 all code for aminoacids

The start codon is AUG. Methionine isthe only amino acid specified by justone codon, AUG.

The stop codons are UAA, UAG, andUGA. They encode no amino acid.Theribosome pauses and falls off the mRNA.


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2.) The mRNA sequence is matched threenucleotides at a time to a complementaryset of three nucleotides in the anticodon

regionof the corresponding tRNA molecule.


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3.) tRNA pick up the amino acid from thecytoplasm, and carries it to the site of

protein synthesis.

Nucleic Acids and Protein Synthesis ppt.pdf

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