Molecular Basis of Inheritance

Question 1

Human DNA

Answer 1

3.3 x 10^9 bp of nucleotides in the DNA of haploid chromosomes

Question 2

Nucleotides

Answer 2

N-glycosidic linkage- Nitrogenous base is attached to OH of 1’C of deoxyribose or ribose sugar

Phosophoester linkage- Phosphate group attached to OH of 5’C of deoxyribose or ribose sugar

Question 3

Polynucleotide

Answer 3

Two nucleotides are joined by 3’-5’ phosphodiester linkage. OH of 3’C of pentose sugar of one nucleotide is attached to the phosphate group of 5’C of another nucleotide

Question 4

5’ end of polynucleotides

Answer 4

Free Phosphate group at 5’C of the pentose sugar

Question 5

3’ end of polynucleotides

Answer 5

Free OH group at 3’C of the pentose sugar

Question 6

Friedrich Miescher

Answer 6

Identified DNA in 1869

Named it ‘Nuclein’

Present in the nucleus and acidic

Question 7

Maurice Wilkins and Rosalind Franklin

Answer 7

Obtained DNA images from X-ray crystallography

Question 8

James Watson and Francis Crick

Answer 8

Proposed the double-helix model of DNA in 1953

Question 9

Erwin Chargaff

Answer 9

Elucidated that the DNA contains equal amounts of adenine and thymine and in the same way guanine and cytosine

Question 10

DNA double helix

Answer 10

Antiparallel strands, coiled in a right-handed fashion

Backbone- sugar-phosphate

Bases are bonded by hydrogen bonds and projected inside

Adenine bonds to thymine by two hydrogen bonds

Guanine bonds to cytosine by three hydrogen bonds

Pitch- 3.4 nm and 10 bp in each turn

Question 11

Central Dogma

Answer 11

Proposed by Francis Crick in 1958

The flow of genetic information from DNA → RNA → Protein

Question 12

Nucleoid

Answer 12

Found in prokaryotes

The region where DNA is concentrated within a cell associated with positively charged proteins

Question 13

Histones

Answer 13

Positively charged basic proteins, rich in lysine and arginine

Eight molecules of histones associated with DNA to form a nucleosome

Question 14

Nucleosome

Answer 14

DNA associated with histones octamer

200 bp of DNA in each nucleosome

Appear as beads on chromatin threads

Question 15

Euchromatin

Answer 15

Loosely packed and lightly stained part of chromatin

Shows active transcription

Question 16

Heterochromatin

Answer 16

Densely packed and darkly stained part of chromatin

Inactive for transcription

Question 17

Transforming principle

Answer 17

Frederick Griffith in 1928

He concluded that there was some transforming principle in the heat-killed S-strain, which transformed R strain Streptococcus pneumoniae to virulent

Question 18

Avery, MacLeod and McCarty

Answer 18

Demonstrated that the DNA caused the bacterial transformation

They showed that proteases and RNAases did not affect transformation, whereas DNAase inhibit transformation

Question 19

Alfred Hershey and Martha Chase

Answer 19

Unequivocal proof of DNA as genetic material in 1952

They worked on bacteriophages

Radioactive 35S labelled- protein capsule

Radioactive 32P labelled- DNA

Question 20

RNA as a genetic material

Answer 20

Present in many viruses, known as a retrovirus

E.g. TMV, QB bacteriophage, etc.

ds RNA- reovirus, etc.

Question 21

Semiconservative DNA replication

Answer 21

Proposed by Watson and Crick

Experimentally proved by Matthew Meselson and Franklin Stahl in 1958 using 15N isotope in the growing medium for E.coli

Taylor and colleagues worked on Vicia faba using radioactive thymidine

Question 22

DNA-dependent DNA polymerase

Answer 22

Main enzyme for replication

Polymerisation in 5’→3’ direction

Question 23

DNA ligase

Answer 23

Join the DNA strand, which is synthesised discontinuously during replication

Question 24

DNA helicase

Answer 24

Unwind DNA at the origin of replication forming replication fork

Question 25

Transcription

Answer 25

Synthesis of RNA from DNA Template strand- 3’→5’ DNA Coding strand- 5’→3’ DNA, has the same sequence as newly synthesised RNA strand

Question 26

DNA-dependent RNA polymerase

Answer 26

Catalyses transcription Polymerisation in 5’→3’ direction

Question 27

Transcription unit

Answer 27

Reference point with respect to the coding strand (5’→3’, DNA) Promoter- present at 5’ end of a structural gene, RNA polymerase binds here Terminator- at 3’ end of the coding strand

Question 28

Cistron

Answer 28

A segment of DNA coding for polypeptide Monocistronic- eukaryotes Polycistronic- prokaryotes

Question 29

Exons

Answer 29

Coding sequence of DNA expressed in mature and processed RNA

Question 30

Introns

Answer 30

Interrupted sequence which are spliced in mature RNA

Question 31

Translation

Answer 31

Formation of polypeptide from RNA mRNA- template for protein synthesis tRNA- adapter molecule, brings amino acids and reads codon on mRNA rRNA- structural and catalytic role

Question 32

Eukaryotic transcription

Answer 32

RNA polymerase I – 28S, 18S, 5.8S rRNA RNA polymerase II – hnRNA (mRNA precursor) RNA polymerase III – tRNA, 5S rRNA, snRNA

Question 33

hnRNA processing

Answer 33

Splicing – removal of introns and joining together of exons Capping – addition of methyl guanosine triphosphate at 5’ end Tailing – addition of adenylate residues (200-300) at 3’ end

Question 34

Marshall Nirenberg

Answer 34

Deciphered first the 64 triplet codons for 20 amino acids present in protein

Question 35

Start codon

Answer 35

AUG Codes for Methionine

Question 36

Stop codons

Answer 36

UAA, UAG, UGA They do not code for any amino acids

Question 37

tRNA

Answer 37

Structure- 2° structure like clover leaf, 3° like inverted L Anticodon loop- complementary mRNA codon for specific codon Acceptor arm- binds to amino acid DHU loop, TψC loop and variable loop Function- Adapter molecule, brings amino acid for translation and reads codon

Question 38

Translation

Answer 38

Occurs in cytoplasm The first step is charging of tRNA, aminoacylation or binding of tRNA to amino acid Peptide bond formation takes place between the amino acid of growing chain and newly brought amino acid in two sites present in the large subunit of ribosomes

Question 39

Ribozyme

Answer 39

Catalytic RNA 28S rRNA in bacteria

Question 40

Untranslated regions (UTR)

Answer 40

Regions on mRNA, which are not translated Present on both 5’ and 3’ ends Required for efficient translation

Question 41

Francois Jacob and Jacque Monod

Answer 41

First elucidated transcriptionally regulated system in lac operon

Question 42

Operon

Answer 42

Present in prokaryotes Contains multiple genes, which are regulated by a promoter and an operator E.g. lac operon, val operon, his, ara, trp, operon, etc.

Question 43

lac operon

Answer 43

i gene- repressor (negative regulation) Structural genes- z – beta-galactosidase (β-gal) y – permease a – transacetylase Inducer – lactose or allolactose

Question 44

Human genome project (HGP)

Answer 44

Started in 1990, Completed in 2003 3 x 109 base pairs (haploid) 20,000-25,000 genes Largest gene- Dystrophin gene of the X chromosome (2.4 million bp) Smallest gene- SRF/TDY gene of the Y chromosome (14 bp)

Question 45

SNPs

Answer 45

Single nucleotide polymorphism Single base differences exist at 1.4 million places in the human genome

Question 46

Sequence annotation

Answer 46

Assigning different regions of genome according to function

Question 47

Expressed Sequence Tags (ESTs)

Answer 47

Identifying all the genes, which are expressed as RNAs

Question 48

DNA Fingerprinting

Answer 48

Developed by Sir Alec Jeffreys Involves identifying of repeated DNA sequences Satellite DNA forms smaller peaks and shows a high degree of polymorphism

Question 49

VNTR

Answer 49

Variable number of tandem repeats Mini-satellite Number and position differs from person to person Flanked by restriction sites

Question 50

Southern blotting

Answer 50

Transfer of electrophoresis separated DNA to nitrocellulose or nylon membrane and detection by probe hybridisation Used to detect DNA sample in blood or tissue