XII: Chapter 6- Molecular basis of inheritance Flashcards
What is the haploid content of human DNA?
3.3 x 10^9 bp
What type of chemical compound is deoxyguanosine?
Nucleoside
What type of chemical compound in deoxycytidine?
Nucleoside
What type of chemical compound is uridine?
Nucleoside
DNA was first identified by
Friedrich Meischer
When was DNA first identified?
1869
What did Friedrich Meischer name DNA?
Nuclein
How is uniform distance maintained between the two strands of DNA?
A purine always pairs with a pyrimidine, which maintains a uniform distance between them.
In which direction are the two chains of DNA coiled?
RIght handed
Histones are rich in which amino acids?
Lysine and arginine
What is the length of DNA wrapped around a histone octamer?
200 bp
While working with which bacteria did Griffith give his transforming principle?
Streptococcus pneumoniae
Why do the S strain Streptococcus pneumoniae produce smooth and shiny colonies?
Because they have a mucous (polysaccharide) coating
Which scientists described the biochemical nature of Griffith’s transforming principle?
Avery, MacLeod and McCarty
The unequivocal proof that DNA is the genetic material came from
Hershey-Chase experiments
Which scientists proved that DNA replicates semi-conservatively?
Meselson and Stahl
How could the heavy DNA in Meselson Stahl experiment be distinguished from normal DNA?
By centrifugation in a cesium chloride density gradient
Which experiment was performed by Taylor et al to prove the semiconservative nature of DNA?
Radioactive thymidine was used to detect distribution of newly synthesised DNA in the chromosomes of Vicia faba
Which phosphates of deoxynucleoside triphosphates are high energy phosphates?
Two terminal phosphates
In which direction can DNA dependent DNA polymerase catalyse polymerisation?
5’ -> 3’
Which strand of DNA is known as the template strand?
strand with 3’ -> 5’ polarity
Which strand of DNA is known as the coding strand?
strand with 5’ -> 3’ polarity
Towards which ends of DNA are promoter and terminator flanked?
Promoter= 5' end of coding strand Terminator= 3' end of coding strand
What is a segment of DNA which codes for a polypeptide called?
Cistron
Monocistronic genes are found in
Eukaryotes
Polycistronic genes are found in
Prokaryotes
How many DNA dependent RNA polymerase catalyse the transcription of RNA in bacteria?
one
How many DNA dependent RNA polymerase catalyse the transcription of RNA in eukaryotes?
At least 3
RNA polymerase I polymerises the transcription of
rRNAs (28s, 18s, 5.8s)
RNA polymerase III polymerises the transcription of
tRNA, 5s rRNA and snRNAs
RNA polymerase II polymerises the transcription of
hnRNA (precursor of mRNA)
In capping, which molecule is added to the hnRNA? Towards which end of RNA is it added?
Methyl guanosine triphosphosphate, 5’ end
In tailing what is added to the hnRNA?. Towards which end of RNA is it added?
Adenylate residues (200-300), 3’ end
Which physicist suggested that in order to code for 20 amino acids, the code should be made of 3 nucleotides?
George Gamow
Which scientist developed the cell free system using which the genetic code was deciphered?
Marshall Nirenberg
What is Severo Ochoa enzyme?
Polynucleotide phosphorylase
The genetic code is nearly universal, exception to this are
mitochondrial codons, some protozoans
Three stop codons exist in the genetic code. How many tRNA exist for these stop codons?
Zero
Which letter does the tRNA resemble?
Inverted L
What happens in the first phase of translation?
Amino acids are activated in the presence of ATP and linked to the cognate tRNA
Charging of tRNA is also known as
Aminoacylation of tRNA
Which unit of ribosome encounters mRNA?
Smaller subunit
How many sites are present in the larger subunit of ribosome for the amino acids to bind to?
2
A transational unit in mRNA codes for
Polypeptide
The untranslated regions in mRNA have no function. True/false?
False. The UTRs are required for efficient translation process.
WHat binds to stop codon for terminalisation of translation?
Release factor
Which is the predominant site for regulation of gene expression in prokaryotes?
Control of the rate of transcriptional initiation
What regulate the ability of RNA polymerase to recognise start sites for transcription?
Accessory proteins
Which scientists elucidated the lac operon?
Monod and Jacob
Does the lac operon have a polycistronic or a monoscistronic structural gene?
Polycistronic structural gene
In the i gene of lac operon, ‘i’ refers to
Inhibitor
Which protein does the z gene of lac operon code for? What is its function?
z gene codes for β-galactosidase which hydrolyses lactose to form galactose and glucose.
Which protein does the y gene of lac operon code for? What is its function?
y gene codes for permease which increases permeability of the cell to β-galactosidase.
Which protein does the a-gene of lac operon code for?
a-gene codes for transacetylase.
The human genome project was closely associated with the rapid development of a new area in biology called
Bioinformatics
How many genes are present in Human DNA?
30,000
Expand ELSI.
Ethical, legal and social issues (implications)
How long did the Human Genome Project take?
13 years
Name a free living non pathogenic nematode whose complete DNA has been sequenced?
Caenorhabditis elegans
Which plants were completely sequenced in the Human Genome Project?
Arabidopsis and rice
What are expressed sequence tags?
Expressed sequence tags (ESTs) are fragments of mRNA sequences
What was the sequence annotation method used in human genome project?
Sequencing the whole set of genome and then assigning different regions in the sequence with functions.
Which were the commonly used hosts and vectors in human genome project?
The commonly used hosts were bacteria and yeast and the vectors were called as bacterial artificial chromosomes (BAC) and yeast artificial chromosomes (YAC).
DNA sequencers used in human genome project worked on the principle of a method developed by
Frederick Sanger
WHo developed the method for determination of amino acid sequences in proteins?
Frederick Sanger.
Which was the last chromosome to be completely sequenced? When was it completely sequenced?
Chromosome 1, 2006
How were genetic and physical maps on the genome developed?
Using the information of polymorphism of restriction endonuclease recognition sites and some repetitive DNA sequences known as microsatellites.
How many bases are present in the average gene?
3000 bases
Which is the largest gene? How many base pairs does it have?
Dystrophin, 2.4 million bases
What percent of the genome codes for proteins?
< 2%
Which chromosomes have the maximum and the minimum number of genes? How many genes are present on them?
Max- chromosome 1, 2968
Min- chromosome y- 231
How many locations have been identified by scientists where single base DNA differences occur?
1.4 million
The bulk genomic DNA form a __1___ peak while the satellite DNA form the __2___ peak.
1 and 2 refer to
1- major
2-minor
DNA can be classified into many categories such as mini satellite, micro satellite,etc based on
Base composition (A:T rich or G:C rich)
Length segment
Number of repetitive segments
Allelic sequence variations have been described as DNA polymorphism if more than one variant at a locus occurs in human population with a frequency
> 0.01%
Who developed the technique of DNA fingerprinting?
Alec Jeffreys
Alec Jeffreys initially developed the technique of DNA fingerprinting using a satellite DNA that shows a very high degree of polymorphism, as a probe which was called
Variable Number of Tandem Repeats
Which blotting technique is used in DNA fingerprinting?
Southern blot
VNTR belongs to a class of satellite DNA referred to as
Mini satellite
The size of VNTR varies from
0.1 to 20 kb
What is base ratio?
G+C
Base ratio in organisms of the same species can vary. True/False.
False. Base ratio is constant for any species
What is the base ratio for humans?
1.55
WHat are the non histone proteins found in prkaryotes which bind DNA called?
Polyamines
Which has more DNA content as compared to RNA content- heterochromatin or euchromatin?
euchromatin
What is the base ratio of eukaryotes?
> 1
What is the base ratio of prokaryotes?
<1
80% of all RNAs are
rRNAs
5% of all RNAs are
mRNAs
15% of all RNAs are
tRNAs
Which are the smallest RNAs?
tRNAs
Which are the longest RNAs?
mRNAs
rRNAs are synthesised in
Nucleolus
mRNAs are synthesised in
Nucleoplasm
tRNAs are synthesised in
Nucleoplasm
Which type of RNA is the most stable?
rRNA
Which type of RNA is the least stable?
mRNA
Insoluble RNA is also known as
rRNA
Soluble RNA is also known as
tRNA
What do the P site, A site and E site in ribosome stand for?
Peptidyl site
Aminoacyl site
Exit site
How many loops does the clover leaf model of tRNA have?
3
How many arms does the clover leaf model of tRNA have?
5
Which is the largest loop of clover leaf model of tRNA?
DHU loop
What is the function of DHU loop of clover leaf model of tRNA?
Binding aminoacyl tRNA synthetase
How many N-bases are present in DHU loop of clover leaf model of tRNA?
8to 10
How many N-bases are present in TΨC loop of clover leaf model of tRNA?
7 N bases
WHat is the function of TΨC loop of clover leaf model of tRNA?
Helps in binding two ribosomal subunits during photosynthesis
Is the short variable arm present in all tRNA?
No
Where is the CCA sequence present in tRNA?
On amino acid attachment site’s 3’ end.
WHere does the amino acid bind in tRNA?
The amino acid loaded onto the tRNA by aminoacyl tRNA synthetases, to form aminoacyl-tRNA, is covalently bonded to the 3’-hydroxyl group on the CCA tail.
If recombination occurs in a cistron it is called
Recon
If mutation occus in a cistron it is called
Muton
Double stranded RNA is found in which viruses?
Reovirus, wound tumour virus
What is the function of small nuclear RNA?
Splicing
How many ori do prokaryotes have?
One
Eukaryotes have many ori in their DNA. True/false?
True
Which enzyme opens the DNA to form a replication fork?
Helicase
What prevent the replication fork of DNA from closing?
Single stranded binding proteins
Which enzyme is called DNA gyrase in prokaryotes?
Topoisomerase
Which enzyme removes the coiling tension created by Helicase enzyme in DNA?
Topoisomerase
What is the function of RNA primase in DNA replication?
It synthesises a small stretch of RNA at the free 3’ end of the DNA strand
What happens to the RNA primer synthesised by RNA primase during DNA replication?
It is converted into DNA by DNA polymerase II
Which DNA polymerase synthesises the new DNA strand in 5’ to 3’ direction?
DNA polymerase III
Which are the major and minor repair enzymes in DNA replication?
DNA Polymerase III
DNA polymerase II
What are the fragments of DNA formed during DNA replication from lagging strand called?
Okazaki fragments
What is the core subunit of RNA polymerase made of?
two alpha (2α), one beta (β), one beta prime (β’) and one omega (ω)
What is TATA box?
Sequence that is recognised by sigma factor (σ) during transcirption of DNA.
What is the TATA box called in eukaryotes? WHat is its sequence?
Hogness box
TATAAAA…
What is the homologue of TATA box in prokaryotes? What is its sequence?
Pribnow box
TATAAT…
What is the size of TATA box?
10bp to 30 bp
What is the size of CAT box?
40 bp to 70 bp
What is CAT box?
Sequence that is recognised by sigma factor (σ) during transcirption of DNA.
When RNA polymerase binds on the promoter region, DNA helix unwinds. The opened stretch of DNA is called
Transcription bubble
Which is the sense strand of DNA?
The strand running in 5’ -> 3’ direction
Where is mRNA modified post-transcriptionally?
Nucleoplasm
Which was the first discovered codon?
UUU- phenylalanine
The codon UUC codes for
Phenylalanine
The codon CCC codes for
Proline
The codon AAA codes for
Lysine
The codon GGG codes for
Glycine
The codon CUC codes for
Leucine
The codon UGG codes for
Tryptophan
Which amino acids are not degenerate in reference to the genetic code?
Tryptophan and methionin
In yeast, UGA codes for
Tryptophan
In the human mitochondria, which is the stop codon?
AGA and AGG
What is transversion (point mutation)?
A purine base is replaced by a pyrimidine base and vie versa
What is transition (point mutation)?
A purine base is replaced by another purine.
OR
A pyrimidine base is replaced by another pyrimidine base.
How do UV rays cause mutations in genetic code?
Affects DNA by forming thymine dimers
How do X rays cause mutations?
Deaminating, dehydroxylase nitrogenous bases forming peroxides and oxidise deoxyribose
What is the wobble hypothesis? Who proposed it?
According to the wobble hypothesis, an amino acid is identified by the first two nitrogenous bases, and the third nitrogenous base of a codon is a wobble. It was proposed by Francis Crick.
How many initiation factors are required in prokaryotes and eukaryotes for the initiation of translation?
Prokaryotes-3
Eukaryotes- 9
What is called translation initiation complex?
rRNA-tRNA-mRNA complex
Which enzymes link amino acids to their corresponding tRNA molecules?
Aminoacyl-tRNA synthetases
What are the functions of P site and A site of ribosome?
the P site holds the peptide chain and the A site accepts the tRNA.
During elongation of peptide chain in translation, which molecule is hydrolysed for energy?
GTP
During the charging of tRNA which molecule is hydrolysed as a source of energy?
ATP
How many release factors (for translation) are present in prokaryotes and eukaryotes?
Prokaryotes- 2
Eukaryotes- 1
What is an inducible operon?
Substrate has to be added to carry out protein synthesis
What is a repressible operon?
In such operon, the substrate is added to stop the protein synthesis.
The regulatory gene in inducible and repressible operons are represented by
Inducible- i
Repressible- r
What is the example of repressible operon?
Tryp-operon
What is the function of transacetylase enzyme?
Transfer acetyl group to β-galactosidase
What is an aporepressor in reference to an operon?
It is a protein molecule that is synthesised by the regulatory gene which may bind to the operator and prevent the transcription.
What is a corepressor in reference to an operon?
Non-protein part that attaches to the repressor protein, activates it and stimulates it to bind to the operator region to prevent transcription.
Southern blotting is used for blotting which molecule?
DNA
Northern blotting is used for blotting which molecule?
RNA
Western blotting is used for blotting which molecule?
Proteins
Eastern blotting is used for blotting which molecule?
There is nothing like eastern blotting (Different types of blotting include- Northern, Southern and Western blotting)
What is the principle of DNA fingerprinting?
RFLP- restriction fragment length polymorphisim
What is the length of minisatellite (in DNA)?
11-60 bp repeating upto 100 times
What is the length of microsatellite (in DNA)?
5-6 bp repeating upto 10 - 100 times
What is the science of matching the prints of fingers, thumbs, toes and skin called?
Dermatoglyphics
Which is the smallest gene in human genome?
Testis determining factor on Y-chromosome
