Biology II chapter 1 - MOLECULAR GENETICS

fill in the blank

Three main components of nucleotides:

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

• The ____ and _____ groups form the backbone of each strand, alternating with each other.

1. sugar

• The specific pairing of the ______ bases _____ with thymine (in RNA, uracil - U) and _____ with guanine holds the strands together by _____ bonds.

1. nitrogenous

2. adenine

3. cytosine

4. hydrogen

genetic information

• The specific sequence of these base pairs along the DNA strand carries the _____. 

nucleotides form

dna

__?__ (the long molecule that stores all genetic information) → ____ (a specific segment of DNA that carries instructions, often to make a protein) → _____ (An alternative version of a gene)

DNA

____ (the long molecule that stores all genetic information) → __?__ (a specific segment of DNA that carries instructions, often to make a protein) → _____ (An alternative version of a gene)

gene

____ (the long molecule that stores all genetic information) → _____ (a specific segment of DNA that carries instructions, often to make a protein) → __?__ (An alternative version of a gene)

allele

3 steps with keywords:

• helicase enzyme

• 5′ - 3′ direction

• Okazaki fragments

• Replication forks

🧬 DNA Replication Mechanism

• Initiation: begin at origins → ___?___ unwinds the DNA by breaking H2 bonds → ______ proteins stabilize the unwound strands & prevent them from rejoining → Topoisomerase acts ahead of helicase, relieve ______ preventing knots/tangles.

1. helicase enzyme

• Initiation: begin at origins → _____ unwinds the DNA by breaking H2 bonds → ___?___ stabilize the unwound strands & prevent them from rejoining → Topoisomerase acts ahead of helicase, relieve ______ preventing knots/tangles.

2. Single-strand binding proteins

• Initiation: begin at origins → _____ unwinds the DNA by breaking H2 bonds → ______ stabilize the unwound strands & prevent them from rejoining → Topoisomerase acts ahead of helicase, relieve ___?___ preventing knots/tangles.

3. supercoiling

• ___?___: Primase lays down RNA primers → DNA polymerase adds nucleotides in 5′ - 3′ direction → Leading strand synthesized continuously → Lagging strand synthesized discontinuously as Okazaki fragments → DNA polymerase replaces RNA primers with DNA → DNA ligase seals gaps.

elongation

• Elongation: Primase lays down RNA primers → ________ adds nucleotides in 5′ - 3′ direction → Leading strand synthesized continuously → Lagging strand synthesized discontinuously as Okazaki fragments → _________ replaces RNA primers with DNA → DNA ligase seals gaps.

• DNA polymerase

• Termination: ______ (Y-shaped region) meet or reach end → RNA primers removed & replaced with DNA → DNA ligase seals backbone → Two identical DNA molecules (semi-conservative).

• Replication forks

regulatory sequences (promoter, enhancers/silencers) + coding sequences (exons, introns) + UTRs + terminator = gene of what???

eukaryotes

• Promoter: DNA sequence where RNA polymerase and transcription factors bind to start transcription.

• Coding region: sequence that is transcribed into RNA and often translated into protein.

• Terminator: sequence signaling the end of transcription.

general structure of gene

________: sequence that is transcribed into RNA and often translated into protein.

• Coding region

_____: sequence signaling the end of transcription.

Terminator

_____: DNA sequence where RNA polymerase and transcription factors bind to start transcription.

Promoter

The process of copying a gene’s DNA sequence into RNA called _____

Transcription

The process of synthesizing a protein from the mRNA sequence.

Translation

to convert genetic information in mRNA into a functional protein.

• Occurs in the cytoplasm, on ribosomes.

• mRNA is read in codons (three-nucleotide sequences).

• tRNA molecules bring the correct amino acids according to the codon sequence.

• Amino acids are linked together by peptide bonds, forming a polypeptide chain → folds into a functional protein.

to create an RNA copy of the gene that can leave the nucleus for protein synthesis.

• Occurs in the nucleus (in eukaryotes).

• RNA polymerase binds to the promoter, unwinds DNA, and synthesizes pre-mRNA (complementary to the DNA template strand).

• In eukaryotes, pre-mRNA is processed: introns are removed, exons are spliced together, a 5′ cap and 3′ poly-A tail are added → mature mRNA.

gene muation

all is correct

🧪 Causes of Gene Mutations

• Spontaneous Mutations: Occur naturally during DNA replication or repair processes.

• Induced Mutations: Result from exposure to environmental factors such as radiation, chemicals, or viruses.

Example: In sickle cell anemia, a single nucleotide change causes a glutamic acid to be replaced by valine in hemoglobin, altering its function

Substitution

Example: A frameshift mutation occurs when nucleotides are inserted or deleted in numbers not divisible by three, shifting the reading frame and potentially altering the entire protein

Insertion/Deletion:

• it happens because DNA is very long, but it needs to be compact enough to fit inside a cel

• when a DNA double helix twists on itself, like a phone cord that gets over-twisted

• The ____ and _____ groups form the backbone of each strand, alternating with each other.

2. phosphate

Example: A mutation in the gene for hemoglobin can cause sickle cell disease, where the altered protein leads to misshapen red blood cells .

Missense Mutation:

Mutation

│

├── Spontaneous (natural errors)

│ ├── In germ cells (egg/sperm) → Hereditary (passed to offspring)

│ └── In somatic cells (body) → Non-hereditary (not passed on)

│

└── Induced (caused by mutagens: radiation, chemicals, viruses)

├── In germ cells → Hereditary

└── In somatic cells → Non-hereditary

diagram flow (Spontaneous → Germline vs Somatic → Hereditary vs Non-hereditary)

Which part of DNA actually carries genetic information?

The sequence of nitrogenous bases

Why can one gene make multiple proteins in eukaryotes?

Alternative splicing of RNA exons