Understanding DNA: Structure, Function, and Replication

DNA

DNA stands for deoxyribonucleic acid

Blueprint for life

It is a complex molecule that controls the characteristics of organisms

Function of DNA

It stores coded instructions about how to make proteins and directs cell division, growth, and function

Eukaryotic cells

Cells that have a nucleus containing their DNA and membrane-bound organelles like mitochondria

Prokaryotic cells

Simpler and smaller cells that do not have a nucleus, with DNA floating freely in the cytoplasm

Size of DNA in Eukaryotic cells

Larger in size, containing 'junk' DNA

Shape of DNA

Each DNA is made of two strands that twist around each other in a double helix

Components of DNA

Made up of smaller sub-units called nucleotides

Nucleotides

Consist of a nitrogenous base, a pentose sugar, and a phosphate group

Types of nitrogen bases in DNA

There are 4: A = Adenine, T = Thymine, G = Guanine, C = Cytosine

Pentose sugars in DNA

DNA uses deoxyribose sugars, a 5 carbons molecule in a ring

Complementary Base Pairs

Adenine joins with Thymine (A=T) and Guanine joins with Cytosine (G≡C)

Hydrogen bonds in DNA

The pairs of nitrogen bases are held together by weak hydrogen bonds

Sugar-phosphate backbone

The 'sides' of the DNA ladder are made from pentose sugars and phosphate groups

Function of proteins

Proteins like enzymes, hormones, and transport proteins allow DNA to control the metabolic reactions of cells

DNA in mitochondria and chloroplasts

DNA is also found in other organelles such as mitochondria and chloroplasts

DNA in Prokaryotic cells

DNA is smaller in size and circular

Cell types included in Eukaryotic cells

Includes plants, animals, and fungi

Cell types included in Prokaryotic cells

Includes bacteria

Length of DNA in cells

There is approximately 2m of DNA folded into chromosomes that fit in the nucleus of each cell

Gene

A segment of DNA that codes for a specific protein.

RNA

A molecule that helps carry out instructions from DNA.

mRNA (messenger RNA)

Carries a copy of a gene from DNA to a ribosome.

tRNA (transfer RNA)

Brings specific amino acids to the ribosome.

rRNA (ribosomal RNA)

A key part of the ribosome; helps link amino acids together.

Transcription

The process of copying a gene (DNA segment) into a message (mRNA).

Translation

The process of using the instructions in the mRNA to build a protein out of amino acids.

PCR

Polymerase chain reaction; uses multiple cycles of DNA replication (approx 30) to replicate DNA in a sample.

Protein synthesis

The process by which cells make proteins, essential for all life functions.

Interphase

The period during which protein synthesis is always happening.

Gene mutations

Changes to the DNA code, which can be deletions, insertions, substitutions, repeats, and inversions.

Gene expression

The process by which genes are turned on and off, allowing differentiation and specialization of cells.

Stem cell

Cells that remain undifferentiated and can become any type of cell in the body.

Totipotent stem cells

Stem cells that can differentiate into any type of cell.

Multipotent stem cells

Stem cells that can differentiate into multiple types of cells within a certain cell line.

Induced pluripotent stem cells (IPSCs)

Stem cells created by nuclear reprogramming and turning off expressed genes.

Epigenetics

The study of how environmental factors can affect gene expression in individuals and their offspring.

Helicase

An enzyme that unwinds and unzips the DNA helix so it can be copied.

DNA polymerase

An enzyme that adds new DNA nucleotides and joins them together.

Cytoplasm

The part of the cell where mRNA leaves the nucleus and enters after transcription.

Amino acid

The building blocks of proteins, added according to mRNA codons during translation.

Polypeptide chain

A chain formed by linking amino acids together during translation.

Anticodon

A sequence on tRNA that is complementary to the mRNA codon.

Codon

A group of three bases on mRNA that specifies which amino acid to add.