The Biochemical Basis of Heredity

Purine

A and G

Pyrimidine

C, U (rna), T

Nucleoside

N base + pentose sugar

Nucleotide

N base + pentose sugar + phosphate group

Phosphodiester bond

Formed between two mononucleotides by linking the phosphate groups.

Dinucleotide

2 nucleotides

Trinucleotide

3 nucleotides

Oligonucleotides

<20 nucleotides

Polynucleotides

>20 nucleotides

RNA

Single stranded molecule

Nucleases

Digests nucleic acid molecules by breaking phosphodiester bonds.

Leading strand

template for continuous DNA synthesis

Lagging strand

discontinuous DNA synthesis

Spliceosome

Identifies and splices boundaries of introns.

Point Mutation

Single base pair substitution.

Mismatch repair

Checks for errors made when DNA is replicated.

Electrophoretic Separation

Physical method of separation of DNA and RNA based on molecular weight and length of the molecule.

DNA ligases

Joins DNA fragments formed by discontinuous synthesis in DNA replication or by DNA repair pathways.

DNA (Deoxyribonucleic Acid)

• A (Adenine), T (Thymine), C (Cytosine), G (Guanine)

(_______________________)

• The molecule that carries all the genetic information in cells.

• Shaped like a double helix — imagine a twisted ladder.

• Made up of 4 bases: (_______, _________, _______, ______)

Helicase

(_________________)

• An enzyme (a protein that speeds up reactions).

• Function: Unzips the double helix by breaking the hydrogen bonds between base pairs.

• Think of it as the "unzipping scissors" of DNA replication.

Replication Fork

• The Y-shaped area formed after DNA is unzipped by helicase.

• Where new strands of DNA are being built.

Single-Stranded Binding Proteins (SSBs)

Bind to the separated DNA strands to keep them apart.

Prevents the strands from snapping back together before replication is done.

Primase

(____________)

An enzyme that creates short RNA (1) (_______).

DNA polymerase can’t start copying on its own — it needs this "starter piece".

Think of it as laying down a foundation before building a wall.

RNA Primer

A short stretch of RNA nucleotides.

Provides a starting point for DNA polymerase to begin building the new strand.

DNA Polymerase

• The main enzyme that builds the new DNA strand.

• It adds nucleotides (A, T, G, C) one by one, matching them to the original strand.

• Can only build in one direction: 5′ to 3′.

Leading Strand

• The strand that is built continuously in the same direction as the fork is opening.

• DNA polymerase can just keep adding bases one after another — smooth and easy.

(Lagging Strand) (Okazaki)

• Built in the opposite direction of the replication fork.

• DNA polymerase has to work backward in short chunks.

• These chunks are called

Okazaki Fragments

Short pieces of DNA made on the lagging strand.

Each starts with a new RNA primer.

DNA Polymerase I

• Removes the RNA primers used to start the Okazaki fragments.

• Replaces them with DNA nucleotides.

DNA Ligase

• The enzyme that seals the gaps between Okazaki fragments.

• Think of it like glue that connects all the pieces into a smooth strand.

Semi-Conservative Replication

Each new DNA molecule has one original strand and one newly made strand.

This keeps the genetic information consistent and reduces copying errors.

Genome

Full set of DNA in a cell, packaged into chromosomes with histone proteins

genes

Chromosomes contain (_____), A specific segment of DNA that contains the instructions for making one protein.

Think of it as a "recipe" in a cookbook.

(Chromosome) (histones) (46 chromosomes)

(_______________)

A long DNA molecule coiled around proteins (called (______).

Humans have (________________) in most cells.

Contains many genes.

(RNA (Ribonucleic Acid) (mRNA (messenger RNA) (tRNA (transfer RNA)

(rRNA (ribosomal RNA)

(_________________)

A copy of the DNA gene used to build a protein.

Uses uracil (U) instead of thymine (T).

Types:

(_____________)

(_____________)

(_____________)

RNA Polymerase

The enzyme that “reads” the DNA and builds an mRNA copy of the gene.

Promoter

• A region on DNA where RNA polymerase binds to start transcription.

• Like a "start signal" for copying a gene.

Template Strand

The DNA strand that is used as a guide to make mRNA.

Read in the 3′ → 5′ direction.

mRNA (Messenger RNA)

• The copy of the gene made from DNA.

• Leaves the nucleus and goes to the ribosome to make the protein.

Splicing

• Process of removing introns (non-coding regions) and joining exons (coding regions).

• Creates a mature mRNA ready for translation.

5′ Cap and Poly-A Tail

Added to mRNA to protect it and help it get out of the nucleus.

(5′ cap) (Poly-A tail)

• (______) Modified G nucleotide at the front

• (________) Chain of A’s at the end

Ribosome

The "factory" where proteins are made.

Reads the mRNA and links amino acids together.

tRNA (Transfer RNA)

Carries amino acids to the ribosome.

Has an anticodon that matches with a codon on mRNA.

Codon

A group of 3 mRNA bases that codes for 1 amino acid.

Anticodon

A 3-base sequence on tRNA that matches a codon on mRNA.

Ensures the correct amino acid is added.

The building blocks of proteins.

Linked together in the ribosome to form a polypeptide.

• The building blocks of proteins.

• Linked together in the ribosome to form a polypeptide.

A long chain of amino acids.

Will fold into a functional protein.

Start Codon

AUG → signals the beginning of translation.

Stop Codon

Signals the end of translation.

(UAA, UAG, UGA)