Unit 4: DNA and the Central Dogma of Biology

Chromosomes

DNA wrapped around proteins called histones.

Where are chromosomes found?

In the nucleus.

What are sections of DNA called?

Genes.

What are identical copies of chromosomes called?

Chromatids.

What holds chromatids together?

Centromeres.

What is the difference between Eukaryotic vs Prokaryotic chromosomes?

Prokaryotes have circular chromosomes in the cytoplasm (nucleoid), while eukaryotes have linear chromosomes in the nucleus.

Who is Erwin Chargaff?

A chemist who developed Chargaff’s rules.

What do Chargaff’s rules state?

The bases of DNA pair together in a specific order: A with T, and C with G.

Who is Rosalind Franklin?

A British scientist who contributed to DNA structure by using X-ray diffraction.

What is Photo 51?

The famous X-ray image of DNA taken by Rosalind Franklin.

How long did it take to get Photo 51?

100 hours.

Who was Rosalind Franklin’s boss?

Maurice Wilkins.

Who built DNA structures based on Photo 51?

Watson and Crick.

What did Watson and Crick create?

The first accurate model of DNA, a double helix.

What does a DNA nucleotide consist of?

Deoxyribose sugar, a phosphate group, and a nitrogen base.

What form the sides of the double helix?

Alternating sugar and phosphate molecules.

What are the rungs of the DNA ladder?

Paired nitrogenous bases.

What holds the two sides of DNA together?

Hydrogen bonds.

How many hydrogen bonds are between A and T?

2 hydrogen bonds.

How many hydrogen bonds are between G and C?

3 hydrogen bonds.

What are hydrogen bonds?

Weak bonds.

When are hydrogen bonds helpful?

During DNA replication.

Who proved that DNA is the molecule for genetics?

Frederick Griffith.

What was Griffith searching for?

A vaccine for streptococcus.

What were the two varieties of bacteria Griffith studied?

One with a capsule and one without.

What was Part 1 of Griffith's experiment?

Injected mice with live encapsulated bacteria, causing pneumonia and death.

What was Part 2 of Griffith's experiment?

Injected mice with live non-capsulated bacteria, which resulted in their survival.

What was Part 3 of Griffith's experiment?

Injected mice with heat-killed encapsulated bacteria, resulting in health.

What was Part 4 of Griffith's experiment?

Injected mice with dead encapsulated and live non-capsulated bacteria, leading to pneumonia.

How did non-capsulated bacteria cause disease?

Through DNA transformation, they gained the ability to make a capsule.

What is DNA?

A nucleic acid present in all living cells.

What does DNA contain?

Instructions that determine the traits needed for survival.

What is the length of DNA in human cells?

Approximately 2 meters.

What does DNA give each organism?

Unique characteristics.

What is another definition of genes?

Segments of nucleotides on chromosomes that instruct traits.

What do prokaryotic chromosomes form?

Loose loops in the cell's cytoplasm.

Where is DNA located in prokaryotes?

In the nucleoid region.

What does the suffix 'old' imply?

Like; it relates to the nucleus.

What is RNA?

A mirror copy of a segment of DNA (a gene), delivered to ribosomes to make proteins.

What determines the order of amino acids?

The order of bases on the RNA.

What are proteins?

Molecules made of amino acids necessary for body structure and regulation.

What structures can RNA also make?

Ribosomes (rRNA) and transfer RNA molecules (tRNA).

What is the sugar in RNA?

Ribose.

What replaces Thymine in RNA?

Uracil.

How many strands does RNA have?

One.

What is DNA replication?

The process by which DNA makes a copy of itself.

What unwinds DNA during replication?

DNA helicase.

What is the replication fork?

The junction where DNA strands split.

What is DNA polymerase?

An enzyme that adds nucleotides to create new DNA strands.

What is semi-conservative DNA?

One original strand is saved in each new DNA double helix.

What are Okazaki fragments?

Severed pieces of DNA that are bound by DNA ligase.

What does transcription mean?

The process of making a working copy of an original DNA segment.

Where does mRNA move after transcription?

To a ribosome through the nuclear membrane.

What is tRNA's role?

To translate and match amino acids to the mRNA code.

What are codons?

Three nitrogenous bases grouped together in mRNA.

What is the basic building block of a protein?

An amino acid.

What is an anticodon?

The code on tRNA that is complementary to mRNA.

What is a mutation?

A change in the nucleotide-base sequence of a gene.

What causes mutations?

Mutagens.

What are mutagens?

Agents that change the DNA sequence.

Types of chromosomal mutations?

Deletions, Insertion, Substitution, Translocation, Duplication, Inversion.

Example of a substitution mutation?

Sickle cell anemia where A is replaced by T.

What is a point mutation?

Substitution of one base for another.

What is a frameshift mutation?

A base is added or removed, shifting the reading frame.

What is a silent mutation?

A base change that results in the same amino acid.

What is a nonsense mutation?

A codon is changed to stop codon.

Possible consequences of a mutation?

Improved trait, No change, Harmful trait.

What do proteins detect and correct mutations?

Proteins made by cells.

Where must a mutation occur to be passed genetically?

In the gametes (sperm or egg).

Why do most genetic mutations not affect us?

Not all mutations are harmful.