DNA STRUCTURE Flashcards
The passing of genetic information from parent to child through the genes in sperm and egg cells.
HEREDITY
A section of DNA that contain the set of instructions or hereditary traits.
GENE
Threadlike structures made of protein and a single molecule of DNA that serve to carry the genomic information from cell to cell.
Chromosome
Long-chain polymeric molecules that is made up of monomers called nucleotides.
Nucleic acid
DNA
Strands:
Sugar:
Nitrogenous Bases:
Strands: Double-stranded, double helix
Sugar: Deoxyribose
Nitrogenous Bases:
Adenine=Thymine, Cytosine=Guanine
RNA
Strands:
Sugar:
Nitrogenous Bases:
Strands: Single-stranded
Sugar: Ribose
Nitrogenous Bases:
Adenine=Uracil, Cytosine=Guanine
Swiss chemist who first identified DNA in the late 1860s.
He called it “nuclein” from the nuclei of white blood cells in pus from soiled bandages.
FRIEDRICH MIESCHER
FRIEDRICH MIESCHER
Swiss chemist who first identified DNA in the late 1860s.
He called it “______” from the nuclei of white blood cells in pus from soiled bandages.
nuclein
Characterizes and names the compounds ribonucleic acid and deoxyribonucleic acid, and a
“tetranucleotide” structure of DNA.
PHOEBUS AARON LEVENE
Shows amounts of the bases Arginine and Thymine, Guanine and Cytosine are equal.
ERWIN CHARGAFF
Deduce DNA’s double helix conformation.
JAMES WATSON & FRANCIS CRICK
Deoxyribonucleic Acid
Function
DNA replicates and stores genetic information.
It is a blueprint for all genetic information contained within an organism.
DNA structure
RNA structure
DNA consists of two strands, arranged in a double helix.
RNA only has one strand,
DNA length
RNA length
Longer polymer
variable in length, but much shorter
DNA sugar
RNA sugar
Deoxyribose
Ribose
DNA bases/ Base pairs
RNA base/ Base pairs
Adenine (‘A’), Thymine (T’), Guanine (‘G’) and Cytosine (‘C’).
Adenine and Thymine pair (A-T)
Cytosine and Guanine pair (C-G)
_________
Adenine (‘A”), Guanine (‘G”) and Cytosine
(‘C’), Uracil (‘U’)
Adenine and Uracil pair (A-U)
Cytosine and Guanine pair (C-G)
DNA location
RNA location
DNA is found in the nucleus, with a small amount of DNA also present in mitochondria.
RNA forms in the nucleolus, and then moves to specialized regions of the cytoplasm depending on the type of RNA formed.
DNA reactivity
RNA reactivity
Due to its deoxyribose sugar, which contains one less oxygen-containing hydroxyl group, DNA is a more stable molecule than RNA
RNA, containing a ribose sugar, is more reactive than DNA and is not stable in alkaline conditions.
DNA UV sensitivity
RNA UV sensitivity
DNA is vulnerable to damage by ultraviolet light.
RNA is more resistant to damage from UV light than DNA.
PRIMARY STRUCTURE
• Nucleic acids are a long chain or polymer of repeating subunits, called____\.
nucleotides
• Each nucleotide subunit is composed of three parts:
- A five-carbon (pentose) sugar
- A phosphate group
- A base
PENTOSE (FIVE-CARBON) SUGAR
• DNA contain the sugar____
• RNA contain the sugar_____
• Both sugars have an oxygen as a member of the five-member ring
• The sugars differ only in the presence or absence (“deoxy”) of an oxygen in the 2 position.
The remarkable versatility of RNA is critically dependent on this hydrogen group
deoxyribose
ribose
• Gives DNA and RNA the property of:
• Acid (a substance that releases an H+ ion or proton in solution) at physiological nu hence the name “nucleic acid!”
PHOSPHATE GROUP
NUCLEOTIDE
NITROGEN BASE
PHOSPHATE - GROUP
SUGAR
NITROGENOUS BASES
• Organic molecules that contain nitrogen.
• Crucial role in the structure of nucleotides.
• Characterized by ring structures including both carbon and nitrogen atoms.
Main categories:
•______- double ring structure (Adenine & Guanine)
•______- single ring structure (Cytosine, Thymine in DNA, & Uracil in RNA
Purines
Pyrimidines
FORMATION OF NUCLEIC ACID CHAINS
• DNA and RNA are formed through a series of steps:
(1) a base attached to a sugar is a
_____
(2) a nucleoside with one or more
phosphates attached is a_____, and
(3) nucleotides are linked by_____ between adjacent nucleotides to form a DNA or RNA chain.
nucleoside
nucleotide
5′ to 3′
phosphodiester bonds
• Connects the phosphate group to the nucleoside, forming a nucleotide.
• Occurs between the 5’-carbon of the sugar and the phosphate group.
Phosphoester bond
• Forms between the 3’-OH (hydroxyl) group of one nucleotide and the 5’-phosphate of another nucleotide.
• Creates the sugar-phosphate backbone of DNA/RNA.
Phosphodiester bond
• The two chains have anti- parallel polarity.
It means, if one chain has the polarity 5’→3’, the other has 3’ →5’.
DNA POLARITY
A-DNA
• Base Pairs Per Turn:
• Morphology
• Screw Sense:
11 bp/turn
Broad and short
Right-handed (twists in a clockwise direction)
Narrow and deep
Wide and shallow
• forms under low humidity (about 75%) and high salt concentrations.
• It is a right-handed helix but has a wider diameter compared to B-DNA.
• The base pairs are tilted from the helical axis, rather than being perpendicular as in B-DNA.
A-DNA
B-DNA
• Base Pairs Per Turn:
• Morphology:
• Screw Sense:
10 bp/turn
Long and thin
Right-handed
• is the most common form of DNA in living cells.
• Found under normal physiological conditions (aqueous environment, moderate salt concentrations, and about 92% humidity).
• Bases are perpendicular to the helical axis.
B-DNA
Z-DNA
• Base Pairs Per Turn:
• Morphology:
• Screw Sense:
12 bp/turn
Long and thin
Left-handed (twists in a counterclockwise direction)
• has a zigzag backbone, giving it a distinct appearance.
• Forms under high salt conditions and in regions rich in alternating purine-pyrimidine sequences (like CG repeats).
Z-DNA
– First Level of DNA Organization
DNA DOUBLE HELIX (2 nm)
• The _____is the fundamental structural form of DNA.
• It has a diameter of_____
• DNA is composed of two complementary strands that run____ (one 5′ → 3′, the other 3′ → 5′).
• The ______forms the outer structure, while the nitrogenous bases (A, T, G, C) pair via hydrogen bonding in the center.
DNA double helix
2 nanometers (nm).
anti-parallel
sugar-phosphate backbone
: Hydrophobic interactions between adjacent base pairs further stabilize the helix.
Base Stacking
The double helix structure was first described by_____ in 1953, based on X-ray diffraction data from_____
Watson and Crick
Rosalind Franklin.
Second Level of DNA Organization
CHROMATIN FIBRIL (10 nm) –
• The chromatin fibril is a___nm fiber made up of_____ separated by linker DNA.
• They are the basic unit of chromatin, composed of DNA wrapped around_____ proteins.
10 nm
nucleosomes
histone
– Third Level of DNA Organization
30 nm CHROMATIN FIBRIL (SOLENOID)
• The ____nm chromatin fibril is formed when the nucleosomes coil further into a helical structure, called the_____ model.
30 nm
solenoid
Fourth Level of DNA Organization
SUPERCOILED STRUCTURE
• The supercoiled structure further condenses the____nm fiber into higher-order chromatin loops.
• These loops are formed by scaffolding proteins that help organize the DNA into a compact, efficient structure.
• _____allows the entire DNA molecule to fit inside the nucleus.
30 nm
Supercoiling
The chromatin can be in two main forms:
• _______– Loosely packed and transcriptionally active (genes can be expressed).
• ______– Densely packed and transcriptionally inactive.
Euchromatin
Heterochromatin
– Fifth and Highest Level of DNA Organization
CHROMOSOME
• ______are the highest level of DNA compaction, formed during cell division (mitosis and meiosis).
• During_____ of mitosis, chromatin condenses into distinct chromosomes, making the DNA highly compact and easier to segregate into daughter cells.
Chromosomes
prophase
Humans have 46 chromosomes (23 pairs):
• 22 pairs of______
• 1 pair of_____
autosomes (non-sex chromosomes)
sex chromosomes (XX in females, XY in males)
Each chromosome consists of:
• Two sister chromatids (identical copies of DNA), connected at a region called the_____.
• _____(repetitive DNA sequences at chromosome ends) that protect the DNA from degradation.
centromere
Telomeres
- The ____is the fundamental level of DNA organization.
- DNA is packaged into ____by wrapping around histone proteins.
- Further coiling into the ______enhances compaction.
- _____and scaffolding proteins condense DNA further into highly compact domains.
- During cell division, DNA is fully condensed into______, ensuring proper segregation.
DNA double helix (2 nm)
nucleosomes (10 nm)
30 nm fiber (solenoid)
Supercoiling
chromosomes
