Exam 2

Chromosome

Large DNA molecule with genes, found in nucleus. Humans have 46 (23 pairs).

Number of Chromosomes

46 total (23 pairs): 23 from mom, 23 from dad.

Autosomes

22 pairs of non-sex chromosomes. Carry most trait info.

Sex Chromosomes

1 pair (XX = female, XY = male). Determine biological sex.

Male vs. Female Chromosomes

Female = XX, Male = XY. Y has SRY gene for testes.

DNA Structure

Double helix. Made of nucleotides: sugar, phosphate, base.

DNA Bases

Adenine (A), Thymine (T), Cytosine (C), Guanine (G). A-T, C-G.

Base Pairing Example

A pairs with T, C with G. Example: AATCG → TTAGC

DNA Replication

DNA copied before cell division. Each strand is a template.

Replication Process

Helicase unzips DNA. DNA polymerase builds new strands. Makes 2 identical DNAs.

PCR (Polymerase Chain Reaction)

Lab technique to make many DNA copies.

PCR Steps

Heat to separate strands → cool to add primers → DNA polymerase builds new DNA. Repeats to amplify.

Genome

All DNA in an organism. Includes genes + non-coding DNA.

STR (Short Tandem Repeat)

Short, repeated DNA sections. Vary per person—used in forensics.

Gel Electrophoresis

Separates DNA by size. STRs show as bands = DNA profile.

CODIS

DNA database used by law enforcement. Stores STR profiles.

Protein Structure

Proteins have 4 levels: Primary: amino acid chain, Secondary: coils and folds, Tertiary: 3D shape, Quaternary: multiple chains together.

Gene Expression

The process of making a protein from DNA: Transcription: DNA → mRNA, Translation: mRNA → protein.

Regulatory vs. Coding Sequences

Regulatory: controls when, where, how much protein is made; Coding: tells the cell what amino acids to use.

Transcription Process

RNA polymerase reads DNA and builds mRNA using the DNA as a template.

DNA to mRNA Base Pairing

A → U, T → A, C → G, G → C. Example: TACG → AUGC.

Location of Transcription

Happens in the nucleus of eukaryotic cells.

Translation Process

Ribosomes read mRNA and use tRNA to build a chain of amino acids (a protein).

Codons vs. Anticodons

Codons: 3-letter mRNA codes for amino acids; Anticodons: tRNA parts that match codons during translation.

Location of Translation

Happens in the cytoplasm at a ribosome.

Genetic Code is Universal

Almost all life uses the same codons to make the same amino acids, so genes can work across species.

Amino Acids and Codons

20 amino acids, 64 codons (3-letter codes), Each codon = 1 amino acid or a stop signal.

Start Codon

AUG = start codon. Codes for methionine, tells the ribosome where to begin.

Transgenic

An organism with a gene from another species (genetically modified).

Recombinant Gene

A custom gene made by mixing coding and regulatory parts from different sources.

Creating a Transgenic Organism (Yeast/Spider Silk)

Scientists put the spider silk gene into yeast using a vector so the yeast makes silk protein.

GMO

An organism with DNA changed by genetic engineering.

Insulin Production

Scientists put the human insulin gene into bacteria, which then make human insulin for medicine.

Gene Therapy

Adding healthy genes to fix faulty ones to treat or cure genetic diseases.

Ethics of Genetic Engineering

Concerns include health risks (like eating GMOs), environmental effects, and human gene editing issues.

Mutation

A change in DNA sequence that can affect proteins, cause disease, or create new traits.

Mutation’s Role in Evolution

Mutations create differences in DNA that drive evolution by natural selection.

Point Mutation

Changes one DNA base — might or might not affect the protein.

Missense, Silent, Nonsense Mutations

Missense: changes amino acid; Silent: no change to amino acid; Nonsense: causes early stop, shortens protein.

Frameshift Mutation

Caused by adding or removing DNA bases — shifts how the gene is read and changes the whole protein.

Insertion vs. Deletion Mutation

Insertion: adds bases; Deletion: removes bases. Both can mess up how the gene is read.

Rearrangement Mutation

Changes large DNA sections — can change gene structure and how it works.

Inversion vs. Translocation Mutations

Inversion: flips a DNA piece; Translocation: moves DNA to a new chromosome. Both affect protein function.

Protein Shape and Function

A protein’s job depends on its shape, which comes from its amino acid order and folding.

Mutagen

Something that causes mutations — like UV light, radiation, or smoking.

Gene Therapy for Sickle Cell

Replaces faulty gene in blood cells using a virus so cells can make healthy hemoglobin.

Turning Genes On/Off with Gene Therapy

Can activate helpful genes (like fetal hemoglobin) or silence harmful ones to treat disease.

CRISPR

A tool that edits DNA using a guide RNA and enzyme to cut at a specific spot.

How CRISPR Edits DNA

CRISPR cuts DNA at a target spot, and the cell repairs it — can fix or replace genes.

Somatic vs. Germ-line Cells

Somatic: body cells, changes affect only that person; Germ-line: sperm/egg cells, changes can be passed to kids.

How CRISPR Changes Can Be Passed to Children

If CRISPR edits germ-line cells, the change can be inherited. Somatic cell changes stay with the person.

Sickle Cell Trait

Person has one normal and one sickle gene — usually no symptoms but can pass it to children.

Why Sickle Cell Trait Can Be Good

It helps protect against malaria, so it’s beneficial in places where malaria is common.

Why Cells Reproduce

To grow, fix damage, and replace old cells.

Tissues That Don’t Do Mitosis

Nerve and heart muscle cells don’t divide in adults.

Interphase

Cell grows, works, and gets ready to divide (G1, S, G2).

G1 Phase

Cell grows and makes more parts (cytoplasm and organelles).

S Phase

DNA is copied so each chromosome has two chromatids.

G2 Phase

Cell checks for DNA errors and prepares for mitosis.

Mitosis

Nucleus divides so each new cell gets the same chromosomes.

Prophase (Mitosis)

Chromosomes condense, nucleus breaks down, spindle forms.

Metaphase (Mitosis)

Chromosomes line up in the middle, spindle attaches.

Anaphase (Mitosis)

Sister chromatids are pulled to opposite sides.

Telophase (Mitosis)

Nucleus reforms, chromosomes relax, division almost done.

Cytokinesis

Cytoplasm divides → two new daughter cells.

G0 Phase

Resting phase — cells not dividing (like neurons).

Cell Cycle Checkpoints

Points where the cell checks if it’s safe to keep dividing.

G1 Checkpoint

Checks cell size, nutrients, and growth signals.

S Checkpoint

Checks DNA for errors during copying — bad errors → apoptosis.

G2 Checkpoint

Makes sure DNA was copied correctly before mitosis.

Mitosis Checkpoint

Checks if chromosomes are lined up and ready to split.

Carcinogen

Anything that causes cancer (e.g., smoking, UV, radiation).

Proto-oncogene

Normal gene that tells cells to divide when needed.

Normal Proto-oncogenes

Help cells divide only when they’re supposed to.

Mutated Proto-oncogenes

Become oncogenes that make cells divide too much.

Tumor Suppressor Gene

Slows cell division, fixes DNA, or causes cell death if needed.

Normal Tumor Suppressor Genes

Stop cell division when there’s a problem.

Mutated Tumor Suppressor Genes

Can’t stop damaged cells from dividing → more mutations.

Sporadic vs. Genetic Cancer

Sporadic: happens from life events; Genetic: inherited mutations (e.g. BRCA1/2).

Steps of Cancer Progression

Starts with one cell → benign tumor → more mutations → malignant → spreads.

Contact Inhibition

Normal cells stop dividing when crowded; cancer cells ignore this.

Anchorage Dependence

Normal cells need to stick to something to divide; cancer cells don’t.

Angiogenesis

Cancer makes new blood vessels to feed the tumor.

Benign vs. Malignant Tumors

Benign: slow, don’t spread; Malignant: fast, invade other areas.

Metastasis

Cancer spreads to new body parts and forms new tumors.

Conventional Cancer Treatments

Surgery: removes tumor; Chemo: kills fast-growing cells; Radiation: damages DNA in cancer cells.

Targeted Cancer Therapy

Treats specific mutations in cancer cells, spares healthy ones.

Immunotherapy

Boosts the immune system to attack cancer cells.

6 Ways to Lower Cancer Risk

1. Don’t smoke; 2. Stay at a healthy weight; 3. Get vaccinated (e.g. HPV); 4. Avoid too much sun; 5. Eat healthy; 6. Get regular cancer screenings.

Genetics

The study of how traits are passed from parents to children.

Haploid vs. Diploid

Diploid: 46 chromosomes (body cells); Haploid: 23 chromosomes (sex cells).

Homologous Chromosomes

Chromosome pairs (one from each parent) with the same genes, possibly different versions (alleles).

Replicated vs. Unreplicated Chromosome

Replicated: two identical chromatids; Unreplicated: one DNA strand.

Gamete

Sex cells (sperm and egg), made by meiosis, and combine to form a baby.

Meiosis

Cell division that makes 4 non-identical haploid sex cells from 1 diploid cell.

Phase Before Meiosis

Interphase – DNA is copied and cell prepares to divide.

Prophase I (Meiosis)

Chromosomes pair up, cross over, and nucleus breaks down.

Metaphase I (Meiosis)

Chromosome pairs line up in the center and spindle attaches.

Anaphase I (Meiosis)

Pairs split apart, moving to opposite sides; chromatids stay together.

Telophase I (Meiosis)

Cell splits into 2 haploid cells, each still with chromatids.