MOLECULAR BIOLOGYby Dr.rer.nat.Tri Yudani MR, MAppSc

DNA MoLECULE of HEREDITY

• DNA/RNA structures• GENETIC code• Transcription

DNAOverview:

Background/history

DNA structure

Genetic information in eukaryotic

A Short History1869 - Miescher isolated DNA the first time1953 - Watson and Crick proposed the double

helix as the structure of DNA1957 - Kornberg discovered DNA polymerase1961 - Marmer and Doty discovered DNA

renaturation1962 - Arber, Nathans and Smith discovered

restriction endonucleases1966 - Nirenberg, Ochoa, and Khorana figured

out the genetic code

• DNA (deoxyribonucleic acid) is a double helix: two strands of genetic material spiraled around each other.

• Everyone’s chemical structure of DNA is the same, the only difference is in the ordering of base pairs.

What is DNA?

BUILDING BLOCK of DNA

• Nucleotides consist of a sugar, phosphate and nitrogenous base

Nitrogenous base of DNA

Purine nucleotides• A - Adenine• G - Guanine

Pyrimidine nucleotides

• T - Thymine• C - Cytosine

Chemical composistion of DNA

DNA strand extend from 5’ to 3’

• The DNA back-bone was connected by phosphodiester bond

Strand of DNA A-A-C-T-G-A-T-A-G-G-T-C-T-A-G T-T-G-A-C-T-A-T-C-C-A-G-A-T-C

POLYNUCLEOTIDE FORMATION

DNA structure Watson-Crick double helix

• The two helical polynucleotide chain coil around the common axis. The chains are antiparalel in polarity

• Purine and pyrimidine bases are inside the helix, whereas the phosphate and deoxyribose units are on the outside.

DNA base composition is governed by Chargaff’s Rule

• DNA has equal number of A and T residue (A-T) and equal number of G and C residue (G-C)

• DNA base composition range from 25-75% G+C content.

RNA (ribonucleic acid)

• Component = DNA except for nitrogenous base is replaced by Uracyl

RNA STRUCTURE

rRNA

From DNA to chromosome

• Humans have 23 pairs of chromosomes.

• A part of chromosome that dictates a particular trait is called a gene.

Chromosome map

• two chrom arms are referred to as p and q (short and long respectively). Bands are numbered from the centromere.

• Ex. band 9q34.1 means the 1st subband of the 4th subband of the 3rd band of the long arm of chromosome 9!

GENE

Gene : a sequence within the genome that functions by giving rise to a discrete product (protein or RNA)

Locus: a position on a chromosome at which the gene for a particular trait resides, locus may be occupied by any one of the alleles for the gene.

Allele

• alternate forms of the same gene• The allele occurring most frequently

in a population wild-type (wt) allele (the “normal” allele)

• Wt allele is usually dominant and is expressed as the wild-type phenotype

• Wt allele used as “standard” for comparison of all mutations of the gene/locus

GENE ORGANISATION

Operon:• Is a unit of gene expression and

regulation including structural genes and control elements in DNA recognised by regulator gene product/s.

Gene organization

PROKARYOTE

Dogma of molecular biology

genome < transcriptome <proteome

1 gene 10 or more proteins

DNA Replication

• Components of Replication process:

• helicase• DNA ligase• DNA polymerase

• VIDIO DNA rep

GENE EXPRESSION

Stages of gene expression

DNA transcription

RNA processing

Protein synthesis

post-transcriptionalmodification

DNA pre-RNA

Pre-RNA m-RNA

m-RNA protein

glycosylation, lipidolationlimited proteolysis

initiationelongationtermination

initiationelongationtermination

splicing, editing,encapping

Transcription process

TRANSCRIPTION IS A PROCESS OF TRANSFER GENETIC INFORMATION FROM DNA INTO RNA

• REQUIRE :Enzyme RNA polymerase• Eukariot : RNA polymerase II• Prokariot : RNA polymeraseDNA template4 Nucleotide (ATP, GTP, CTP dan UTP)

• RNA elongate in 5’ 3’ direction• begin start codon (AUG )and ending

with stop codon (UAA; UAG dan UGA)

• RNA polymerase• DNA template

strand or antisense strand

• DNA coding strand = mRNA

Transcription machine in bacteria

Transcription maschine

STAGES IN TRANSCRIPTION

Eukaryotic : mRNA processing

• A eukaryotic mRNA is modified in the nucleus during or shortly after transcription

Cont- mRNA processing

• 1. addition of a methylated cap at the 5’ end

• Addintion of poly(A) at the 3’ end• Splicing via splicesosome

mRNA is exported from nucleus to cytoplasm only after all modifications have been completed