Ch 6. Molecular Basis of Inheritance (stack 1) Flashcards
Name the pentose sugar present in DNA
Deoxyribose sugar
Name the pentose sugar present in RNA
Ribose sugar
Mention an example for purine
Adenine /Guanine ·
Mention an example for pyrimidine
Cytosine/Thymine
Name the bond present between pentose sugar and nitrogen base in a nucleoside
N - glycosidic bond
Name the bond present between a nucleoside and the phosphate group
Phosphoester bond
Name the bonds present between the two strands of a DNA molecule
Hydrogen bond
Name the bond formed between sugar and phosphate back bone of single stranded DNA
Phosphodiester bond
What is the alternative chemical name of thymine?
5-methyl uracil
Name the nitrogenous base present in DNA but not in RNA
Thymine
Name the nitrogenous base present in RNA but not in DNA
Uracil
Name the nucleoside present only in DNA
Deoxythymidine
Name the nucleoside present only in RNA
Uridine
What was the observation of Erwin Chargaff for a double stranded DNA?
For the double stranded DNA the ratios between Adenine and Thymine and Guanine and Cystisineare constant and equals to one.
Which nitrogenous base provides additional stability to DNA?
Thymine
State the central dogma of molecular biology
It states that genetic information flows from DNA –> RNA –> Proteins
What is reverse dogma of molecular biology?
The flow of genetic information from RNA –> DNA –> RNA –> Proteins is called reverse dogma
What is nucleosome?
A nucleosome is the basic subunit of chromatin in eukaryotes in which two turns of DNA are wrapped around a group of eight positively charged proteins called histones or the histone octamer.
Name the proteins which form the core of nucleosomes
Histone proteins.
Mention any one basic amino acid present in large quantities in the histone proteins of nucleosomes
Lysine/Arginine
How many base pairs (bp) of a DNA helix are found in a typical nucleosome?
200 bp
What is chromatin?
The repeating units of nucleosomes with the DNA strand showing beads-on-string structure inside the nucleus is called chromatin
What is euchromatin
The loosely packed, lightly stained and transcriptionally active chromat in is called euchromatin
Define heterocbromatin
The more densely packed, darkly stained and transcriptionally inactive chromatin is called heterochromatin.
Replication in the region of euchromatin would be faster. Justify.
Because it is loosely packed, separation and unwinding of DNA strands becomes easy.
Replication in the region of heterochromatin would be slow. Justify
Because it is densely packed, separation and unwinding of DNA strands becomes relatively difficult
Heterochromatin is transcriptionally inactive when compared to euchromatin. Give reason?
It is because, the heterochromatin is not easily accessible by the enzymes as it is more densely packed than the euchromatin
Mention the four nitrogen bases present in DNA
Adenine, guanine, cytosine and thymine
Mention the four nitrogen bases present in RNA
Adenine, guanine, cytosine and uracil
List the nucleosides of DNA
Adenosine, guanosine, cytidine and thyrnidine
Mention the nucleosides of RNA
Adenosine, guanosine, cytidine and uridine
If a double-stranded DNA has 20% of cytosine, calculate the percent of adenine in the DNA
According to Chargaffs mle - No. of purines= No. of pyrimidines
Therefore, 20% C - G 20% = 40%
30% A-T 30% =60%
Explain the central dogma of molecular biology with a schematic representation.
Francis Crick proposed the Central dogma in molecular biology, which states that the genetic information flows from DNA –> RNA –> Protein
Draw a labelled diagram of nucleosome
How many base pairs of DNA are present in a typical nucleosome?
Mention the types of proteins present in a nucleosome
200bp per nucleosome. It consists of histone octamer (assembly of 8 histone subunits) and a Hl histone.
The base sequence in one of the DNA strands is TAGCATGAT. Based on this answer the following
- Give the base sequences of its complementa1y strand.
- How are these base pairs held together in a DNA molecule?
- What was the observation of Chargaff on the base ratio in double- stranded DNA?
- ATCGTACTA
- Through hydrogen bonds
- For a double-stranded DNA, the ratios between Adenine and Thymine and Guanine and Cytosine are constant and equals one.
Explain packaging of DNA in prokaryotes
- In prokaryotes, such as, E. coli, though they do not have a defined nucleus, the DNA is not scattered throughout the cell.
- DNA (being negatively charged) is held with some proteins (that have positive charges) in a region termed as ‘ nucleoid ‘ .
- The DNA in nucleoid is organised in large loops held by proteins.
The length of a DNA molecule in a typical mammalian cell is calculated to be approximately 2.2 meters. How is the packaging of this long molecule done to accommodate it within the nucleus having a size of approximately 6µ?
- In eukaryotes, the packaging of DNA helix is a complex process.
- There is a set of positively charged basic proteins called histones.
- Histones are organized to form a unit of eight molecules called histone octamer.
- The negatively charged DNA is wrapped around the positively charged histone octamer to form a structure called a nucleosome.
- Nucleosomes constitute the repeating unit of a structure in the nucleus called chromatin, thread-like stained (coloured) bodies seen in the nucleus. The nucleosomes in chromatin are seen as ‘beads-on string ‘ structures when viewed under an electron microscope.
- The beads-on-string structure in chromatin is packaged to form chromatin fibres that are further coiled and condensed at the metaphase stage of cell division to form chromosomes.
