Genetics -Nucleic acids

What is the structure of a nucleoside

A nucleoside consists of a nitrogenous base bonded to a five-carbon sugar (ribose or deoxyribose), without any phosphate group attached.

What is the bond between the five carbon sugar and nitrogenous base in nucleosides called

B-Glycosidic bond

What is the bond between a phosphate group and ribose sugar called in nucleotides

Phosphodiester bond

What are the rules of base pairng

Adenine pairs with thymine(2 hyrdrogen bonds), Guanine pairs with cytosine (3 hydrogen bonds), each bond is 2 nmin distance between base pairs in the double helix structure.

What hydroxyl groups are the phosphodiester bonds formed at

the 3' (pyramidines) and 5' (purines) positions of the sugar

DNA backbone is always _____ and why

Hydrophillic. Polar phophate groups can interact with the polar enviroment

DNA helical structure is

right-handed and anti-parallel, allowing base pairs to stack and maximize stability.

DNA helix makes a complete turn every

3.4 nm

Stacked bases are packed ___ to base pairs per turn

0.34 nmper base pair.

How many base pairs per turn

10 base pairs per turn

Spaces between the helical structures are called by virtue of their width

Major groove and minor groove

Why are these grooves needed

Provide a place for proteins (transcription factors /DNA binding proteins ) to interact with DNA

What is the semi-conservative model of DNA

Each strand of DNA serves as a template to form a newcomplementary strand

What are the different forms of DNA

1) B form of DNA - naturally occuring
2) A form - appears when relative humidiy of enivroment is less than 75%
3) Z form - left handed double helix - difficult to observe as it is unstable

What are the unusual structures of DNA

1) Palindromic sequences - sequences that read the same forwards and backwards

2) Hairpin structures - formed when a single strand folds back on itself.

2) Mirror sequences - sequence where a DNA segment has a center of symmetry, meaning the sequence on one side of the center is the same as the sequence on the other side, but in reverse.

4)Inverted repeats - create intrabonds (between the same) - sequences where a DNA strand is followed by its reverse complement. These repeats, also known as palindromes, are common in both prokaryotic and eukaryotic genomes and can form secondary structures like stem-loops or hairpin loops

What is melting temperature of DNA

Temperature when half the bases in a double strand have denatured and formed a single strand. can be monitored at 260 nm.

What is hyperchromic effect

increase in UV absorbance that occurs when double-stranded DNA is denatured into single-stranded DNA. This phenomenon happens because the base pairs in double-stranded DNA stack together, limiting the absorption of UV light, while in single-stranded DNA, the bases are more exposed and can absorb more UV light, leading to a higher absorbance. 

What is hypochromic effect

decrease in ultraviolet (UV) light absorption when DNA transitions from a single-stranded (ssDNA) to a double-stranded (dsDNA) state. This happens because the base-stacking interactions within the dsDNA structure reduce the absorption of UV light compared to the more freely absorbing ssDNA

What is the structure of RNA?

Has a ribose sugar -contains OH group at 2nd carbon
Has uracil instead of thymine

Is single stranded

What is the difference is between uracil and thymine

Uracil is a pyrimidine base found in RNA, while thymine is a pyrimidine base found in DNA. The key difference is that uracil contains a hydrogen atom instead of the methyl group present in thymine.