DNA Structure, Replication, and Genetic Concepts for Biology

DNA (Deoxyribonucleic acid)

Molecule that carries genetic instructions for an organism.

Nucleus

Part of the cell where DNA is found.

Nucleotide

Basic building block of DNA.

○ — ⬟ — ▭

○ = phosphate

⬟ = deoxyribose sugar

▭ = nitrogen base

Deoxyribose Sugar

Sugar molecule found in DNA nucleotides. ⬟ pentagon

Phosphate

Part of the DNA backbone. ○ circle

Nitrogen Base

Chemical base attached to the sugar in DNA.

Usually shown as:

▭ rectangle

The 4 bases:

Adenine (A)

Thymine (T)

Cytosine (C)

Guanine (G)

Complementary Base Pairing

Definition: Bases pair in a specific way in DNA.

Rule:

A pairs with T

C pairs with G

Example:

▭A ═ ▭T ▭C ═ ▭G

DNA backbone

Repeating sugar-phosphate pattern forming the sides of DNA.

Double Helix

Twisted ladder shape of DNA.

sides = sugar-phosphate backbone

middle = base pairs

Gene

Section of DNA that codes for a trait or protein.

Eye colour gene

Chromosome

Coiled structure made of DNA containing many genes.

Trait

An inherited characteristic.

eye colour

dimples

hair type

Protein

Molecule made using DNA instructions that performs functions in the body.

DNA Replication

Process where DNA makes an identical copy of itself.

Purpose:

Before cell division.

Helicase

An enzyme that breaks hydrogen bonds and unzips the DNA double helix during replication.

DNA Polymerase

An enzyme that adds complementary nucleotides to build the new DNA strand during replication.

A → TC → G

DNA Ligase

An enzyme that joins DNA fragments together by sealing gaps in the sugar-phosphate backbone.

Genotype

The allele combination an organism has.

Phenotype

The physical trait or characteristic shown by an organism.

brown eyes

blue eyes

curly hair

Dominant Alles

An allele that only needs one copy to be expressed.

Recessive alles

An allele that needs two copies to be expressed.