Nucleic acids

A **nucleotide**.

The monomer of a nucleic acid: a **phosphate group**, a **pentose sugar** and a **nitrogenous base** joined together.

A **phosphate group**, a **pentose (5-carbon) sugar**, and a **nitrogenous base**.

**Deoxyribose**.

**Ribose**.

**Thymine (T)**.

**Uracil (U)** — it replaces thymine.

**Adenine (A), cytosine (C) and guanine (G)**.

DNA is **double**-stranded (two); RNA is **single**-stranded (one).

**Sugar** (deoxyribose vs ribose), **one base** (thymine vs uracil), and **number of strands** (double vs single).

The **information-carrying** part of a nucleotide — A, C, G and either T (DNA) or U (RNA).

The sugar sits in the **middle** — joined to the **phosphate** on one side and the **base** on the other.

A **double helix** — two strands twisted around each other.

The rule that **A pairs only with T**, and **G pairs only with C**, on the two DNA strands.

**Thymine (T)**.

**Cytosine (C)**.

**Hydrogen bonds** (between the two bases).

**A–T has 2**; **G–C has 3**.

The **bases** (by hydrogen bonds). The sugar–phosphate backbones are not joined to each other.

The two strands run in **opposite directions** to each other.

In DNA, **%A = %T** and **%G = %C**.

**22%** — because %G = %C.

A = T = 30%, so A+T = 60%, leaving **40%** shared by G and C (20% each).

**Watson and Crick**, using X-ray data from **Rosalind Franklin**.

In the **sequence (order) of the bases** A, T, C and G along the molecule.

It is a **long** molecule using a **4-letter** code, so the bases can be ordered in an **enormous** number of ways.

The **order of the bases** (A, T, C, G) along a DNA strand — this order is the stored information.

Its two **complementary strands** back each other up, and the bases sit protected inside the double helix.

A **protein** that **DNA wraps around** to package (condense) it inside eukaryotic cells.

DNA **wraps around** them to **package / condense** the long molecule so it fits inside the cell.

A single long **DNA molecule wound around histones** and condensed into a compact, organised structure.

The DNA molecule is **very long** (about 2 m per human cell) but the cell is tiny, so it must be **condensed** to fit and be protected.

**Eukaryotes** (plants, animals, fungi). Most **prokaryotes do not** use histones.

The **order (sequence)** — rearranging the bases changes the message, like rearranging letters changes a word.

Like **thread around a spool** — the long thread winds up tightly and condenses.

**No** — histones only **package** the DNA. Reading and copying are done by other molecules.

**All of the DNA** of an organism — its complete set of genetic instructions.

Determining the **full order of bases** (A, T, C, G) across an organism's **entire genome**.

A **gene** is one instruction; a **genome** is the **whole instruction book** (all genes + the DNA between).

**No** — some plants and amphibians have larger genomes than humans but are not more complex.

Much of the extra DNA is **non-coding** — it does not code for proteins.

The same DNA bases code for the **same amino acids** in (almost) **every** living thing.

All life inheriting the **same code** is best explained by descent from a **common ancestor**.

The nucleus of **almost any single body cell** (e.g. a white blood cell).

A gamete (egg or sperm) carries only **half** the genome.

**Diagnosing genetic disease / personalising treatment**, and **comparing genomes to map how species are related**.

Concerns over **privacy** and how a person's **genetic data** is stored and used.

**Benefits AND a limitation/ethical concern**, then a clear overall **judgement**.