DNA Replication, Nucleic Acids, ATP, and Properties of Water

Vocabulary practice flashcards covering nucleic acids, DNA replication mechanisms and enzymes, ATP synthesis and hydrolysis, differences between RNA and DNA, prokaryotic vs eukaryotic genetic material, and the physical properties of water.

DNA replication

The process occurring prior to cell division (such as mitosis) where DNA makes identical copies of itself so that each daughter cell receives an identical copy and an identical amount of DNA.

DNA helicase

An enzyme that breaks the hydrogen bonds between complementary base pairs, unwinding the double helix and separating the two strands to expose the bases.

Free nucleotides

Individual nucleotides manufactured in the cell (available in the cytoplasm and nucleus) that complementary base-pair with exposed bases on the template strand during DNA replication.

DNA polymerase

An enzyme that catalyses the formation of strong covalent phosphodiester bonds between adjacent nucleotides (joining the sugar of one nucleotide to the phosphate group of another) to build the sugar-phosphate backbone.

Semi-conservative replication

A form of DNA replication that produces two identical DNA molecules, each composed of $1$ original (old) template strand and $1$ newly synthesised strand.

Sister chromatids

Two identical copies of a replicated chromosome that remain attached to each other (forming an X-like shape) until they are separated during cell division.

Chromosome

A cellular structure consisting of $1$ continuous molecule of DNA supercoiled around histone proteins for structural stability.

Gene

A specific section or sequence of DNA bases on a chromosome that codes for one protein or a polypeptide chain; humans possess approximately $20{,}000$ different genes across $46$ chromosomes ($23$ pairs).

Histones

Proteins around which eukaryotic DNA is supercoiled to provide structural stability and form chromosomes.

Antiparallel strands

The arrangement of the two strands in a DNA double helix running in opposite directions, where the $5'$ carbon/phosphate group points up on one strand and down on the other.

Phosphodiester bond

A strong covalent bond formed via a condensation reaction between adjacent nucleotides in a polynucleotide chain, releasing $1$ water molecule per bond formed.

Purines

The larger category of nitrogenous bases characterized by a double-ring structure, comprising Adenine (A) and Guanine (G).

Pyrimidines

The smaller category of nitrogenous bases characterized by a single-ring structure, comprising Cytosine (C), Thymine (T), and Uracil (U).

Complementary base pairing rule

The rule stating that purines always pair with pyrimidines, where Adenine forms $2$ hydrogen bonds with Thymine ($\text{A}=\text{T}$) and Cytosine forms $3$ hydrogen bonds with Guanine ($\text{C}\equiv\text{G}$).

Eukaryotic DNA

Linear DNA stored inside a nucleus that wraps around histone proteins to form linear chromosomes.

Prokaryotic DNA

Circular, looped DNA found in bacterial cells that is not contained within a nucleus and is not wrapped around histone proteins.

Single-stranded viral nucleic acid

Genetic material found in certain viruses (such as COVID-19 or certain single-stranded DNA viruses) in which the amounts of Thymine and Adenine or Cytosine and Guanine are not equal.

Messenger RNA (mRNA)

A single-stranded RNA molecule that represents a complementary copy of a single gene.

Transfer RNA (tRNA)

A type of RNA responsible for carrying a specific amino acid to the ribosome during protein synthesis.

Ribosomal RNA (rRNA)

A form of RNA that, together with proteins, makes up the structure of ribosomes.

Structural differences between DNA and RNA

DNA is double-stranded, contains deoxyribose sugar, has bases A, T, C, G, and is long (containing many genes); RNA is single-stranded, contains ribose sugar, has bases A, U, C, G, and is short (coding for only $1$ gene).

ATP (Adenosine Triphosphate)

A phosphorylated nucleotide composed of the base adenine, a ribose sugar, and three inorganic phosphate groups, functioning as the primary immediate energy source in cells.

ATP hydrolysis

The breakdown of ATP into ADP and an inorganic phosphate ($\text{P}_i$) through the hydrolysis of its terminal phosphate bond, releasing free energy: $\text{ATP} \rightarrow \text{ADP} + \text{P}_i + \text{Energy}$.

Phosphorylation

The addition of a phosphate group to another substance (such as via ATP hydrolysis), making the phosphorylated substance more reactive and lowering its activation energy.

ATP synthase

The enzyme that catalyses the resynthesis of ATP by joining ADP and inorganic phosphate ($\text{P}_i$) during respiration or photosynthesis.

Oxidative phosphorylation

A method of ATP synthesis occurring in plant and animal cells during aerobic respiration.

Substrate-level phosphorylation

A method of ATP synthesis occurring in plant and animal cells when phosphate groups are transferred directly from donor molecules to ADP.

Photophosphorylation

A method of producing ATP that occurs in chlorophyll-containing plant cells during photosynthesis.

Biological advantages of ATP

Releases energy in manageable, small amounts (less than glucose) and is broken down in a single step, making energy readily and immediately available.

DNA nucleotide vs. ATP structure

A DNA nucleotide contains one phosphate, deoxyribose sugar, and any one of four bases (A, T, C, or G); ATP contains three phosphates, ribose sugar, and only the adenine base.

Dipolar water molecule

A molecule ($\text{H}_2\text{O}$) exhibiting polarity due to an uneven charge distribution: the oxygen atom carries a slightly negative charge ($\delta^-$) and the hydrogen atoms carry slightly positive charges ($\delta^+$), allowing hydrogen bonds to form between molecules.

High specific heat capacity of water

A property resulting from hydrogen bonds holding water molecules together, requiring significant energy to raise its temperature and enabling water to act as a buffer against sudden temperature variations.

Latent heat of vaporisation of water

A property resulting from hydrogen bonding between water molecules that requires a large amount of energy to evaporate $1\,\text{g}$ of water.