Biology: Organisms and their Environment

Ribosomes

Synthesize polypeptides

Science

The observation, identification, experimental investigation, and theoretical explanation of natural phenomena

Scientific method

Standard approach practiced by scientists

Levels of organization

Molecules, molecular biology, cells, anatomy and physiology, ecology, integrative biology

Model organisms

Organisms with consistent behavior and low variability

Evolution

Heritable change in a population of organisms from generation to generation

Structure and function

The relationship where structure determines function

Information

Genetic material provides a blueprint for all biological processes

Energy and matter

Energy is acquired from the environment and used to make molecules and maintain an organism's body

Systems

Interactions between parts create novel structures or functions

Discovery science

Collection and analysis of data without a preconceived hypothesis

Hypothesis

Proposed explanation for a natural phenomenon based on previous observations or experimental evidence. Must be falsifiable

Theory

Broad explanation of some aspect of the natural world, backed by extensive evidence

Peer-reviewed journals

Scientific literature that undergoes evaluation by experts in the field

Open access

Freely sharing research with everyone, inside and outside the scientific community

COVID-19 vaccines

Developed by scientists such as Dr. Kariko, Dr. Weissman, Dr. Tureci, Dr. Sahin, Dr. Corbett, and Dr. Graham

Charles Darwin

English naturalist who proposed the theory of evolution and natural selection

Theory of natural selection

Process which eliminates individuals that are less likely to survive and reproduce in a particular environment, while allowing other individuals with traits that confer greater reproductive success to increase in numbers

Evolutionary change

Changes in genetic material that lead to the formation of new species

Variation in traits

Heritable traits passed from parent to offspring; genetic

Mutation

Heritable change in genetic material that can bring positive changes to an organism

An example of vertical descent with mutation

Genetic epidemiology (SARs-CoV2, virus that causes COVID-19)

Vertical descent with mutation

Genetic material (DNA) passed down generations. Mutations accumulate in the genetic material overtime. Occurs within a lineage

Horizontal gene transfer

Less common than vertical transfer, genes passed from parent to offspring. More common in bacteria (single cell organisms)

Example of horizontal gene transfer

Antibiotic resistance

Gene

Unit of heredity; an organized unit of DNA

Cells

Simplest, functional unit of a living organism

Atavistic trait

Modification of a biological structure whereby an ancestral genetic trait reappears after having been lost through evolutionary change in previous generations

DNA

Double-stranded, helical-shaped molecule that stores genetic material. Provides a blueprint for form and function in living organisms

RNA

Single-stranded molecule that converts genetic material into proteins

Proteins

Molecules that give structure and function to the body

Keith Porter

Biologist known as the 'Father of the Cell' for his work on cell structure

Prokaryotic cells

Simple cells without internal compartmentalization or a membrane-enclosed nucleus

Eukaryotic cells

Cells with internal compartmentalization and a membrane-enclosed nucleus

Plasma membrane

Cell membrane composed of a phospholipid bilayer embedded with proteins

Organelles

Small structures inside the cell with specific functions

Number of chromosomes (sets) in humans

23 pairs of chromosomes

Number of autosomes in humans

22 pairs

XX is

Female

XY is

Male

Haploid (n) - homologous or non-homologous?

One copy of each chromosome
Non-homologous

Diploid (2n)

Two copies of each chromosomes
Homologous

Homologs

Members of a pair chromosome in a diploid species (i.e., homologous chromosomes)

Karyotype

an individual’s complete set of chromosomes

G1 Phase

• Includes the process of cell growth.

• Signalling molecules cause the cell to accumulate molecules that promote progression through the cell cycle

• If the cell passes the restriction point. the cell becomes commited to enter S phase and replicate DNA

S Phase

• Chromosomes replicate

• After replication the two copies stay attached to each other as sister chromatids

• If the cell passes the restriction point, or G1 checkpoint, the cell becomes committed to enter S phase and replicate (synthesize) DNA

• Human cell in G1 has 46 chromosomes (22 pairs + two sex chromosomes)

• The same cell in G2 has 46 pairs of sister chromatids, or 92 chromatids in total 

G2 Phase

Cell synthesizes proteins needed for cell division

Cytoskeleton

Protein network that provides structure and allows for cell movement

Eukaryotic cell cycle

Series of repeated rounds of cell growth and division in eukaryotes

Chromosomes

Discrete units of genetic material consisting of DNA and associated proteins

Mitosis

Cell division that produces two genetically identical daughter cells

Meiosis

Cell division that produces haploid cells from a diploid cell

Bivalent or tetrad

Homologous pairs of sister chromatids that associate with each other

Synapsis

Formation of the synaptonemal complex between homologous chromosomes

Crossing over

Physical exchange of genetic material between sister chromatids — Prophase I

Cytokinesis

Process of dividing the cytoplasm to form two separate daughter cells

Cyclins or cyclin-dependent kinases

Important proteins that help cells move through different stages of their life cycle

Checkpoint proteins

Act like alarms to check if the cell is ready to divide properly

Cancer risk in cell division

If checkpoints fail, it can lead to mistakes in cell division, which may result in cancer

Role of P53 Gene

Also called “The Guardian of the Genome” - a gene that helps prevent cancer formation. Works hard to stop cancer by stopping genes from mutating

Oncogenes

Troublemakers that can bypass the security measures set by genes like P53

Sister chromatids

Two identical copies of a chromosome

Centromere

Region of DNA where sister chromatids associate

Centromere also serves as an attachment site for

Kinetochore (used in sorting chromosomes)

Chromatid

One of the two identical halves of a chromosome, after replication

Mitotic spindle

Part of a cell’s structure that helps sort and organize chromosomes during cell division (mitosis). Made of microtubules

Microtubules

Tiny tubes made of a protein called tubulin

Centrosomes

Cell parts that help organize the microtubules. Command centers for the mitotic spindle

Centrioles

Only in animal cells. Help form the centrosomes

Prophase

• Chromosome Replication: Chromosomes have already been copied, and they exist as pairs of sister chromatids. The centromere (a special region) is also duplicated.

• Example: If the original cell had six chromosomes, after replication, it will have 12 chromatids (6 pairs).

• Chromatid Compaction: The chromatids become tightly packed and can be seen clearly under a microscope.

• Nuclear Membrane Change: The membrane around the nucleus breaks down into small pieces.

Prometaphase

• Nuclear Envelope Breaks: The protective layer around the nucleus falls apart.

• Mitotic Spindle Fully Forms: The structure responsible for moving chromosomes is complete.

• Centrosomes Move Apart: These direct the spindle and go to opposite ends of the cell.

• Fibers Interact with Chromatids: The spindle fibers attach to the sister chromatids.

• Attachment Points: Each chromatid pair attaches to spindle fibers from opposite poles.

Metaphase

• Chromatids Line Up: Pairs of sister chromatids sit in a line at the center, called the metaphase plate.

• Organized in a Row: They're arranged neatly in a single row.

• When Complete: The cell is in metaphase.

Anaphase

• Chromatid Connections Break: The proteins holding the chromatids together let go.

• Tugged Toward Poles: The chromatids are pulled towards opposite ends by the spindle fibers.

• Become Individual Chromosomes: Once separated, they're no longer attached and are now individual chromosomes.

• Poles Move Apart: The opposite ends of the cell move away from each other.

Telophase

• Chromosomes Reach Poles: They arrive at their respective ends and start to spread out.

• Nuclear Membranes Re-Form: The protective layers around the nuclei reassemble.

• Result: Now, there are two nuclei, each with a full set of chromosomes.

Cytokinesis

• Follows Mitosis Quickly: Happens right after cell division.

• Two Nuclei Go to Daughter Cells: Each nucleus goes to one of the new cells.

• Different in Animals and Plants:

  • In animals, the cell constricts like a drawstring to split. (Cleavage furrow)

  • In plants, a cell plate forms a new cell wall between the two.

Chiasma

The point of contact or crossing over between two homologous chromosomes during meiosis. Where genetic material is exchanged between chromatids

Prophase I

• Chromosomes bunch up, forming pairs called bivalents.

• They swap genetic material (crossing-over).

• Nuclear membrane breaks down, and spindle fibers start to form.

Prometaphase I

• Spindle structure is complete.

• Chromatids attach to spindle fibers.

• Sister chromatids of each pair connect to a single pole.

Metaphase I

• Bivalents align along the middle.

• Random arrangement along the plate.

Anaphase I

• Homologous pairs separate.

• Connections between bivalents break.

• Each pair of chromatids moves to a different pole.

Telophase I

• Chromatids reach poles and spread out.

• Nuclear membranes reform.

Cytokinesis in Meiosis I

• Meiosis I ends, forming two haploid cells.

• Haploid means they lack pairs of homologous chromosomes.

Meiosis II

Process is very similar to Mitosis

Cytokinesis in Meiosis II

Cleavage furrows separates the two cells into four cells (haploid). Each daughter cell has a random mix of chromosomes

Sexual reproduction

Requires union of two haploid gametes to form a diploid zygote

Zygote undergoes ___ to create a multicellular organism

Mitosis

Diploid-dominant species

Most animals - gametes are specialized haploid cells

______ are produced through meiosis

Gametes (n)

Haploid-dominant species

Multicellular organism is haploid and only the gametes are diploid

_______ cells produced by mitosis

Reproductive

Ploidy

Total number of chromosomes you have

Euploid

The normal number of chromsomes for your species
“Eu” - EUkaryotic, the true nucleus

Polyploid

3 or more sets of chromosomes
i.e., Triploid (3n), three copies of chromosome 3
Tetraploid (4n) four copies of chromosome 4

Aneuploidy

Abnormal number of a particular chromosome

Nondisjunction

• Can lead to aneuploidy

• Chromosomes do not sort properly during cell division

  • Zygote and its daughter cells will have the wrong number of chromosomes

Mendelian Inheritance

The inheritance of genes that segregate and assort independently (think meiosis)

Non-Mendelian Inheritance

The inheritance of traits through changes in gene expression, not gene or chromosome sequence

Complex traits

Also inherited, trait expression may be influenced by more than one gene, by the environment, or by different genes in people of different ancestry

Character

Term for a general feature of an organism (i.e., seed)

Trait

Term for a variant of a character (i.e., green or yellow)