Week 1 (DNA structure) Flashcards
What are phosphate groups commonly joined to?
C5 (5’) hydroxl of the ribose or deoxyribose sugar
Define genome
The complete store of information in an organisms DNA
What does a nucleotide consist of?
- Nitrogen containg base
- A 5 carbon sugar
- 1 or more phosphate groups
How are nucelotides joined together?
By a phosphodiester linkage between a 5’ C and a 3’ C
Draw the structure of complementary base pairs
What is the difference between nucleoside and nucleotide?
Base + Sugar = Nucleoside
Base + Sugar + Phosphate = nucleotide
energy
Name other functions of nucleotides
- Carry energy in their easily hydrolised phosphoanhydride/ phosphodiester bonds
- Combine with other groups to from co-enzymes
- Act as specific signalling molecules in the cell
What gives a DNA strand chemical polarity?
The way in which the nucleotides are linked together. This polarity in a DNA chain is indicated by referring to one end as the 3ʹ end and the other as the 5ʹ end
List the nucleoside of each base
Draw cytosine thymine and uracil
What is the difference between the sugar used in ribose and in deoxyribose?
Why do organisms differ from one another?
Organisms differ from one another because their respective DNA molecules have different nucleotide sequences and, consequently, carry different biological messages
How are nucleotides linked together and how does this affect polarity?
The nucleotides are linked together covalently by phosphodiester bonds:
a covalent bond is formed between the 5’ phosphate group of one nucleotide and the 3’-OH group of another
Thus, each polynucleotide strand has a chemical polarity; that is, its two ends are chemically different. The 5ʹ end of the DNA polymer is by convention often illustrated carrying a phosphate group, while the 3ʹ end is shown with a hydroxyl.
Explain the structure of DNA
- Two long polynucleotide chains composed of four types of nucleotide subunits. Each of these chains is known as a DNA chain, or a DNA strand.
- The chains run antiparallel to each other
- Hydrogen bonds between the base portions of the nucleotides hold the two chains together
- Nucleotides are composed of a five-carbon sugar to which are attached one or more phosphate groups and a nitrogen-containing base. I
- In the case of the nucleotides in DNA, the sugar is deoxyribose attached to a single phosphate group (hence the name deoxyribonucleic acid), and the base may be either adenine (A), cytosine (C), guanine (G), or thymine (T). 6. The nucleotides are covalently linked together in a chain through the sugars and phosphates, which thus form a “backbone” of alternating sugar–phosphate–sugar–phosphate. These same symbols (A, C, G, and T) are commonly used to denote either the four bases or the four entire nucleotides—that is, the bases with their attached sugar and phosphate groups.
What are the two types of bases?
Pyrimidines and purines
How could information in DNA be duplicated and copied from generation to generation?
The double-stranded nature of the structure: because each strand of DNA contains a sequence of nucleotides that is exactly complementary to the nucleotide sequence of its partner strand, each strand can act as a template, or mold, for the synthesis of a new complementary strand
How does th 3D structure of DNA arise?
From the chemical and structural features of its two polynucleotide chains. Because these two chains are held together by hydrogen-bonding between the bases on the different strands, all the bases are on the inside of the double helix, and the sugar-phosphate backbones are on the outside
This complementary base-pairing enables the base pairs to be packed in the energetically most favorable arrangement in the interior of the double helix. In this arrangement, each base pair is of similar width, thus holding the sugar-phosphate backbones a constant distance apart along the DNA molecule. To maximize the efficiency of base-pair packing, the two sugar-phosphate backbones wind around each other to form a right-handed double helix, with one complete turn every ten base pairs
Draw adenine and guanine
What carbon of the sugar does the base link to?
C1
What is the difference between ribose and deoxyribose?
Ribose has an OH attached to its 2’ C
Deoxyribose has a H attached to its 2’ C
