DNA STRUCTURE Flashcards by Kyra Catedral

The passing of genetic information from parent to child through the genes in sperm and egg cells.

HEREDITY

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A section of DNA that contain the set of instructions or hereditary traits.

GENE

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Threadlike structures made of protein and a single molecule of DNA that serve to carry the genomic information from cell to cell.

Chromosome

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Long-chain polymeric molecules that is made up of monomers called nucleotides.

Nucleic acid

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DNA

Strands:
Sugar:
Nitrogenous Bases:

Strands: Double-stranded, double helix
Sugar: Deoxyribose
Nitrogenous Bases:
Adenine=Thymine, Cytosine=Guanine

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RNA

Strands:
Sugar:

Nitrogenous Bases:

Strands: Single-stranded
Sugar: Ribose
Nitrogenous Bases:
Adenine=Uracil, Cytosine=Guanine

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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

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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

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Characterizes and names the compounds ribonucleic acid and deoxyribonucleic acid, and a
“tetranucleotide” structure of DNA.

PHOEBUS AARON LEVENE

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Shows amounts of the bases Arginine and Thymine, Guanine and Cytosine are equal.

ERWIN CHARGAFF

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Deduce DNA’s double helix conformation.

JAMES WATSON & FRANCIS CRICK

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Deoxyribonucleic Acid

Function

DNA replicates and stores genetic information.

It is a blueprint for all genetic information contained within an organism.

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DNA structure

RNA structure

DNA consists of two strands, arranged in a double helix.

RNA only has one strand,

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DNA length

RNA length

Longer polymer

variable in length, but much shorter

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DNA sugar

RNA sugar

Deoxyribose

Ribose

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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)

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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.

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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.

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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.

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PRIMARY STRUCTURE
• Nucleic acids are a long chain or polymer of repeating subunits, called____\.

nucleotides

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• 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

1. The ____is the fundamental level of DNA organization. 2. DNA is packaged into ____by wrapping around histone proteins. 3. Further coiling into the ______enhances compaction. 4. _____and scaffolding proteins condense DNA further into highly compact domains. 5. 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