Question

Describe two ways DNA is different than RNA. Name two roles that hydrogen bonds play in DNA? What is the difference between 10 nm fiber, 30 nm fiber and the DNA loops? Describe histones. What are they made of (ie the types of subunits). How do they interact with DNA?

Answer 1

Differences between DNA and RNA

1.The pyrimidines in DNA are Thymine and cytosine while the pyrimidines in RNA are Cytosine and Uracil.

2.In DNA the pentose sugar is deoxyribose while in RNA the sugar is ribose

3.DNA is more stable compared to RNA.

4. DNA is generally double stranded, while RNA is mostly single stranded.

Two roles Hydrogen bonds play in DNA

1.Hydrogen bonds are the reason for specificity in pairing of neucleotides.ie,Adenine pairs with thymine and gunaine pairs with cytosine.

2.This specificity is helps in semi-conservative replication of DNA. It also contributes to the stability of the double helix.

10 nm fiber

It is the most basic organisational level of chromatin.10 nm fiber has a beaded string appearance where each bead is called a nucleosome.Each nucleosome consists of a core particle made up of a histone octamer(2 molecules each of H2A H2B H3 and H4)and the two turns that DNA makes around the histone octamer.The length of the core DNA is 146 base pairs.Adjacent nucleosomes are connected by linker DNA whose length varies.

30 nm fiber

The 10 nm fiber can fold into a 30 nm fiber which represents the second level of organiation of chromatin.30 nm fiber resembles a solenoid where each turn consists of 6 nucleosomes. The packaging ratio (length of DNA/length of unit that contains it) of DNA in 10 nm fiber is 6.In 30 nm fiber the packaging ratio is approximately 40.

DNA Loop

When histones are removed from the highest level of organisation of chromatin (metaphase chromosome),a chromosome scaffold made up of non-histone proteins can be seen and loops of DNA is found attached to the scaffold using the scaffold attachments regions (SARs). Such DNA loops are likely to be functional units as well as topological domains, and might be concerened with regulation of gene expression and replication.

Histones.

Histones are a family of evolutionarily conserved proteins that help in the packaging and expression of DNA. The major histone proteins are H1, H2A, H2B, H3 and H4. In addition to these canonical histones there are many variant histones. Substitution of a cnonical histone with a varaint is used for control repair, regulation of transcription and chromosome packaging. N-terminal tails of core histones can be revesibly modified by acetylatin, methylation, phosphorylation etc. and such modifications are also involved in the epigenetic control of gene expression. Histones are basic proteins having a very high affinity for negatively charged DNA. The positive charge of histones allow them to associate with core DNA.

By subunits of histones I'm assuming you meant the subunits of a histone octamer.A histone octamer is made of 4 histone proteins(H2A ,H2B , H3 and H4).Two of each of these proteins are arranged to form a histone octamer.

Histone proteins are simple polypeptides.