THE MOLECULAR BASIS OF INHERITANCE
THE MOLECULAR
BASIS OF INHERITANCE
OVERVIEW: LIFE’S OPERATING INSTRUCTIONS
• In 1953, James Watson and Francis Crick introduced an elegant double-helical model for the structure of deoxyribonucleic acid, or
DNA• DNA, the substance of inheritance, is the
most celebrated molecule of our time• Hereditary information is encoded in DNA
and reproduced in all cells of the body• This DNA program directs the development
of biochemical, anatomical, physiological, and (to some extent) behavioral traits
WATSON AND CRICK
The Discovery of the Molecular Basis Of InheritanceIn the early 1900s, scientists knew that
chromosomes, made up of DNA (deoxyribonucleic acid) and proteins,
contained genetic information.
However, they did not know whether the DNA or the proteins was the actual genetic
material.
In the 1940s, various researchers showed that DNA was the genetic material
In the 1950s, the structure of DNA was determined.
The DNA (Deoxyribonucleic Acid)
The structure of DNA was determined by James Watson and Francis Crick in the early
1950s.
DNA is a polynucleotide; nucleotides are composed of a phosphate, a sugar, and a
nitrogen-containing base.
The sugar in DNA is deoxyribose
The four different bases in DNA are: adenine (A), thymine (T), guanine (G),
and cytosine (C).
DNA
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
C-GG-CA-TG-CG-CT-AT-AT-AA-TA-TA-TC-GC-GT-AC-GG-C
A nucleotide
Structure of DNA
Watson and Crick showed that DNA is a double helix in which
A is paired with T G is paired with C
This is called complementary base pairing because a purine is always paired with a pyrimidine.
Structure of DNA
Single Stranded Polynucleotide Chain
Double Stranded Polynucleotide Chains
Central Dogma
Nucleosome
Hershey-Chase Experiment
Meselson – Stahl’s Experiment
Replicating Fork
The DNA Double Helix
Structure of DNA
Structure of DNA
Replication of DNA
DNA replication occurs during chromosome duplication.
An exact copy of the DNA is produced with the aid of DNA polymerase.
Hydrogen bonds between bases break and enzymes “unzip” the molecule.
Each old strand of nucleotides serves as a template for each new strand.
New nucleotides move into complementary positions are joined by DNA polymerase.
DNA replication
Replication of DNA
Ladder configuration and DNA replication
Gene Expression
A gene is a segment of DNA that specifies the amino acid sequence of a protein.
Gene expression occurs when gene activity leads to a protein product in the
cell.
A gene does not directly control protein synthesis; instead, it passes its genetic information on to RNA, which is more directly involved in protein synthesis.
RNA (ribonucleic acid) is a single-stranded nucleic acid in which A pairs with U (uracil)
G pairs with C.
Three types of RNA are involved in gene expression:
messenger RNA (mRNA) carries genetic information to the ribosomes,
ribosomal RNA (rRNA) is found in the ribosomes,
transfer RNA (tRNA) transfers amino acids to the ribosomes, where the protein product is
synthesized.
The RNA (Ribonucleic Acid)
Structure of RNA
Two processes are involved in the synthesis of proteins in the cell:
Transcription makes an RNA molecule complementary to a portion
of DNA.
Translation occurs when the sequence of bases of mRNA directs
the sequence of amino acids in a polypeptide.
Structure of RNA
The Genetic CodeDNA specifies the synthesis of proteins because it contains a triplet code: every three bases stand for one amino acid.
Each three-letter unit of an mRNA molecule is called a codon.
Most amino acids have more than one codon; there are 20 amino acids with a possible 64 different triplets.
The code is nearly universal among living organisms.
The Genetic Code
The Amino AcidsAmino acids are the building blocks of proteins.
A protein forms via the condensation of amino acids to form a chain of amino acid "residues" linked by peptide bonds.
There are 20 standard amino acids in a genetic code. These are:
1. Phenylalanine2. Serine3. Leucine4. Tyrosine5. Cysteine6. Tryptophan7. Proline8. Histidine9. Glutamine10.Arginine11.Isoleucine
12.Methionine13.Threonine14.Asparagine15.Lysine16.Valine17.Alanine18.Aspartate19.Glutamate20.Glycine
Chemical Structures of Amino Acids
1. Phenylalanine
3. Leucine 4. Tyrosine
2. Serine
5. Cysteine
8. Histidine
6. Tryphophan
7. Proline
Chemical Structures of Amino Acids
Chemical Structures of Amino Acids
9. Glutamine
11. Isoleucine12. Methionine
10. Arginine
Chemical Structures of Amino Acids
13. Threonine 14. Asparagine
15. Lysine 16.Valine
Chemical Structures of Amino Acids
17. Alanine
20.Aspartate19. Glutamate
18. Glycine
Central Concept or " The Central Dogma"
The central concept of genetics involves the DNA-to-protein sequence involving transcription and translation.
DNA has a sequence of bases that is transcribed into a sequence of bases in mRNA.
Every three bases is a codon that stands for a particular amino acid.
Overview of Gene Expression
Overview of Gene Expression
Transcription
During transcription in the nucleus, a segment of DNA unwinds and
unzips, and the DNA serves as a template for mRNA formation.
RNA polymerase joins the RNA nucleotides so that the codons in mRNA are complementary to the
triplet code in DNA.
Transcription and mRNA Synthesis
Transcription Unit
Transcription in Bacteria
Transcription in Eukaryotes
Translation
Translation is the second step by which gene expression leads to protein synthesis.
During translation, the sequence of codons in mRNA specifies the order of amino acids in a
protein.
Translation requires several enzymes and two other types of RNA: transfer RNA and
ribosomal RNA.
Translation
Lac Operon
Review of Gene Expression
DNA in the nucleus contains a triplet code; each group of three bases stands for one
amino acid.
During transcription, an mRNA copy of the DNA template is made.
The mRNA is processed before leaving the nucleus.
The mRNA joins with a ribosome, where tRNA carries the amino acids into position during
translation.
Made By –Anurag Verma
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