Science Test: Topic 2

DNA

• The molecule that carries genetic information and determines the traits of an organism.

Nucleotide

• The basic building block of DNA, consisting of a sugar, a phosphate, and a nitrogen base.

Nitrogen Bases

• The molecules that make up the "rungs" of the DNA ladder: Adenine (A), Thymine (T), Cytosine (C), and Guanine (G).

Double Helix

• The twisted-ladder structure or shape of a DNA molecule.

Gene

• A specific section of DNA that contains the instructions to build one specific protein.

Chromosome

• A tightly coiled structure of DNA and protein found in the nucleus of a cell. Humans have 46 total (23 pairs).

Amino Acid

• The small molecular building blocks that link together to build a protein.

Protein

• A large molecule made of amino acids that does structural or chemical work inside an organism.

Mutation

A change in the nucleotide sequence of an organism's DNA.

Adenine (A) matches only with

• Thymine (T) (The apple falls from the tree)

Cytosine (C) matches only with

• Guanine (G) (The car goes into the garage vice versa)

Transcription (Copying the Code) happens inside…

inside of the cell nucleus

Transcription (Copying the Code) happens…

• The cell opens up a specific section of DNA (a gene). It makes a single-stranded messenger copy called mRNA (messenger RNA).

The RNA difference

• RNA does not use Thymine (T). Instead, it uses Uracil (U).

• Example: A DNA strand of A-T-G transcribes into an mRNA strand of U-A-C.

Translation (Reading the Code) happens where?

At a ribosome in the cytoplasm.

Translation (Reading the Code): What happens?

• The mRNA leaves the nucleus and attaches to a ribosome. The ribosome reads the mRNA bases in groups of three called codons.

Build the Protein

• A helper molecule called tRNA reads each codon and delivers the exact matching amino acid. The ribosome binds these amino acids together into a long chain.

The Final Shape

• Once the amino acid chain is complete, it folds into a specific 3D shape. The shape determines the protein's function.

Types of Mutations: Substitution

One base is swapped out for another (e.g., changing A to G)

Types of Mutations: Insertion

• An extra base is accidentally added to the sequence.

Types of Mutations: Deletion

• A base is accidentally left out or erased.

The Consequences: Harmful Mutations

• Can cause a protein to fold incorrectly, leading to disorders like genetic diseases or cancer.

The Consequences: Neutral Mutations

Do not change the amino acid produced or do not harm the organism (e.g., a mutation causing different colored eyes).

The Consequences: Beneficial Mutations

• Give the organism a helpful new trait that allows it to survive better in its environment (the driving force behind natural selection).