DNA Transcription - Genetics

Ribose

A sugar found in RNA with a hydroxyl group (-OH) at the 2' carbon.

Deoxyribose

A sugar found in DNA that lacks a hydroxyl group at the 2' carbon and has only a hydrogen (-H).

Purines

Double-ring structures including adenine (A) and guanine (G).

Pyrimidines

Single-ring structures including cytosine (C), thymine (T in DNA), and uracil (U in RNA).

5' end of DNA strand

The end of a DNA strand with a phosphate group attached to the 5' carbon of the sugar.

3' end of DNA strand

The end of a DNA strand with a hydroxyl (-OH) group attached to the 3' carbon of the sugar.

Antiparallel

Refers to the orientation of the two strands in dsDNA running in opposite directions, one 5' → 3', the other 3' → 5'.

Phosphodiester bonds

Covalent bonds that link nucleotides in a single strand of DNA.

Hydrogen bonds

Non-covalent bonds holding the two strands together in double-stranded DNA (dsDNA).

Telomeres

Structures at the ends of chromosomes protected by protein complexes to prevent fusion and degradation.

Chargaff's rules

State that the amount of adenine (A) equals thymine (T), and the amount of cytosine (C) equals guanine (G).

Tm (melting temperature)

The temperature at which half of the DNA duplex separates into single strands.

Heteroplasmy

The presence of both normal and mutated mtDNA within a cell, affecting inheritance of mitochondrial diseases.

cpDNA

Chloroplast DNA involved in photosynthesis.

mtDNA

Mitochondrial DNA involved in energy production.

Nucleotide

The building block for DNA consisting of a nitrogenous base, a deoxyribose sugar, and a phosphate group.

dsDNA backbone

Made of sugar (deoxyribose) and phosphate groups, covalently bonded through phosphodiester bonds.

Adenine (A) and Thymine (T)

Pair forming 2 hydrogen bonds in DNA.

Guanine (G) and Cytosine (C)

Pair forming 3 hydrogen bonds in DNA.

Mitochondria per cell

Varies, typically around 100–10,000.

mtDNA genomes per mitochondrion

2–10 copies.

Nuclear genomes

Genome found in the nucleus of cells.

Mitochondrial genomes

Genomes found in mitochondria.

Chloroplast genomes

Genomes found in chloroplasts of plant cells.

What nm wavelength of light does DNA (and RNA) absorb?

260 nm

Coding strand

Matches the RNA sequence (except T for U)

Template strand (antisense strand)

Used as a template for RNA synthesis

How many base pairs is 6.72 kb?

6,720 base pairs.

How many base pairs in the human genome in an egg or sperm? A somatic cell?

• Egg or sperm (haploid): ~3 billion base pairs.

• Somatic cell (diploid): ~6 billion base pairs.

What percent similar are two random human genomes?

Approximately 99.9% similar (0.1% different).

Why does the double helix of DNA have a constant diameter, regardless of the sequence?

A purine always pairs with a pyrimidine (A with T, G with C), ensuring a constant diameter.

What conditions separate the double helix into ssDNA: in PCR vs. in a cell?

• PCR: Heat denatures the DNA strands.

• Cell: Helicase enzyme separates the strands during replication.

Where does the energy come from to synthesize DNA?

Energy comes from the hydrolysis of the high-energy phosphate bonds in deoxynucleoside triphosphates (dNTPs).