BIO160 Unit 3

What does “life begets life” mean

Living organisms arise from other living organisms through reproduction

Why do offspring often resemble their parents?

Parents transmit hereditary information that influences offspring traits

What central question connects reproduction and genetics?

How do organisms transmit biological characteristics and genetic information to their offspring?

What was preformationism?

An outdated belief that a miniature, fully formed organism already existed inside a reproductive cell and simply grew during development

What is cytology?

The study of cells, including their structure, function, organization, and division

What is genetics?

The study of heredity and how genetic information and characteristics are passed from parents to offspring

What is molecular biology?

The study of biological processes involving molecules such as DNA, RNA, and proteins

What is the smallest unit of life?

The cell

What does “Omnis cellula e cellula” mean?

Every cell comes from a preexisting cell.

Who discovered “Omnis cellula e cellula”?

Rudolf Virchow in 1855

What principle of cell theory explains the continuity of life?

New cells arise through the reproduction and division of existing cells, allowing life and genetic information to continue across generation

How do prokaryotic and eukaryotic cells differ in their nuclei?

Prokaryotic cells lack a membrane-bound nucleus

Eukaryotic cells contain a nucleus that houses their genetic material

How does chromosome organization differ between prokaryotic and eukaryotic cells?

Prokaryotes usually have circular chromosomes

Eukaryotes typically have multiple linear chromosomes located inside the nucleus

How do membrane-bound organelles differ between prokaryotic and eukaryotic cells?

Eukaryotic cells contain membrane-bound organelles that perform specialized functions

Prokaryotic cells lack membrane-bound organelles

What is the typical division process of prokaryotic cells?

Binary fission, in which the chromosome is replicated, the DNA copies separate, and the cell divides into two daughter cells

Why was Thomas Hunt Morgan’s fruit-fly research important?

His research helped establish that chromosomes carry hereditary information and play an essential role in transmitting inherited characteristics

What is an origin of replication (ORI)?

A specific location on a chromosome where DNA replication begins, allowing the genetic material to be copied before cell division

What happens first during binary fission?

DNA replication begins at the origin of replication on the circular chromosome, producing a copy of the genetic material

What happens to the duplicated origins of replication during binary fission?

The duplicated ORIs move toward opposite poles of the cell as chromosome replication progresses, helping separate the genetic material

What is the final outcome of binary fission?

Two daughter cells are produced, each receiving a copy of the original chromosome

Why is eukaryotic cell division more complex than prokaryotic division?

Eukaryotic cells contain multiple chromosomes that must be accurately replicated, organized, and separated during cell division

Why do eukaryotic chromosomes have multiple origins of replication?

Multiple ORIs allow DNA replication to begin at several locations simultaneously, making replication of large eukaryotic genomes more efficient

What recognizes replication origins in eukaryotic cells?

The Origin recognition Complex (ORC), which recognizes origins of replication and helps initiate DNA replication

What happens to DNA during interphase?

DNA is replicated during the S phase of interphase, ensuring the cell has a complete duplicated set of genetic information before mitosis

Why aren’t individual chromosomes visible during interphase?

DNA remains relatively uncondensed, meaning chromosomes are not tightly packed into the distinct structures visible during mitosis

What happens to centrosomes during interphase?

Centrosomes duplicate in preparation for forming the mitotic spindle, which helps organize and separate chromosomes during mitosis

What are sister chromatids?

Two identical copies of a replicated chromosome that remain attached at the centromere until they separate during anaphase

What happens during prophase?

Chromosomes condense and become visible, the mitotic spindle begins forming, and centrosomes move toward opposite sides of the cell

How can you recognize prophase in a cell image?

Chromosomes appear condensed and visible but are not yet aligned at the center of the cell

What happens during prometaphase?

Spindle microtubules attach to chromosomes at their kinetochores, allowing chromosomes to begin moving toward the center of the cell

How do kinetochore and nonkinetochore microtubules differ?

Kinetochore microtubules attach to chromosomes and help move them

Nonkinetochore microtubules interact with microtubules from the opposite pole and help elongate the cell

What happens during metaphase?

Duplicated chromosomes align at the metaphase plate, located halfway between the spindle’s two poles, preparing for separation

How can you identify metaphase in an image?

Chromosomes form a line across the middle of the cellm with sister chromatids still attached

What triggers sister chromatid separation during anaphase?

Cohesin proteins connecting sister chromatids are cleaved, allowing the chromatids to separate and become independent chromosomes

What happens to microtubules during anaphase?

Kinetochore microtubules shorten to pull chromosomes toward opposite poles

Nonkinetochore microtubules lengthen to help elongate the cell

When do sister chromatids become individual chromosomes?

During anaphase, when the sister chromatids separate and move toward opposite poles of the cell

What happens during telophase?

Two nuclei form around the separated chromosomes, and the chromosomes begin to decondense as nuclear division finishes

How does cytokinesis differ from mitosis?

Mitosis divides the nucleus and separates duplicated chromosomes

Cytokinesis divides the cytoplasm to produce two separate daughter cells

How does cytokinesis differ in plant and animal cells?

Animal cells form a cleavage furrow that pinches the cell into two, while plant cells form a cell plate that develops into a new dividing wall

What is the usual genetic outcome of mitosis?

Two daughter cells are produced that contain the same genetic information as the original parent cell, maintaining genetic continuity

How can genetically identical cells have different functions?

Through cellular differentiation, cells with the same DNA develop specialized structures and functions by expressing different sets of genes

Prokaryotic Cells

Lack a membrane-bound nucleus and typically contain circular chromosomes

Eukaryotic Cells

Have a membrane-bound nucleus, organelles, and typically multiple linear chromosomes

What is an origin of replication?

A specific location on DNA where replication begins

What does the Origin Recognition Complex do?

Recognizes replication origins in eukaryotes

Binary Fission

Prokaryotic division involving DNA replication, chromosome separation, and division into two cells

Mitosis

Eukaryotic nuclear division that separates duplicated chromosomes into two daughter nuclei

What is the usual genetic outcome of mitosis?

Two daughter nuclei containing the same genetic information.

When followed by cytokinesis, it typically produces two genetically identical daughter cells

What is cellular differentiation, and why is it important?

The process through which cells develop specialized structures and functions

Allows multicellular organisms to develop different tissues despite cells generally containing the same DNA

What is the cell cycle?

The ordered sequence of events involving cell growth, DNA replication, and division

Ensures genetic material is copied and distributed to daughter cells

What are the three periods of the prokaryotic cell cycle?

B period: Time between cell division and DNA replication

C period: DNA replication

D period: Time between completion of replication and cell division

What happens during B period?

The cell grows and performs normal functions

Occurs after cell division but before DNA replication begins

What happens during C period?

The chromosomes undergoes DNA replication

Produces the genetic copies needed for daughter cells

What happens during D period?

DNA replication has been completed

The cell prepares for and completes division into daughter cells

What are the two major parts of the eukaryotic cell cycle?

Interphase: Includes G1, S, and G2

M phase: Includes mitosis and cytokinesis

What happens during G1?

Cell growth and normal cellular functions

Preparation for DNA replication

Cell cycle regulation helps determine whether the cell proceeds toward S phase

What happens during S phase?

DNA synthesis occurs

Each chromosome is duplicated, producing sister chromatids

Ensures genetic material is available for both daughter cells

What happens during G2?

Additional growth and preparation for mitosis

The cell checks whether DNA replication is complete

DNA damage may delay progression into mitosis

What happens during M phase?

Mitosis: Duplicated chromosomes separate into two nuclei

Cytokinesis: Cytoplasm divides, producing two daughter cells

Why must interphase occur before mitosis?

Allows DNA replication and preparation for division

Without successful DNA replication, daughter cells would not receive complete copies of the genetic information

What is cell cycle regulation?

The control of when a cell grows, replicates DNA, and divides

Helps prevent inappropriate division and maintain genetic stability

What three cell cycle checkpoints are emphasized in the lecture?

G1: Checks whether conditions are suitable for DNA replication

S: Monitors DNA replication and damage

G2: Checks readiness for mitosis

What is the purpose of the G1 checkpoint?

Determines whether the cell should proceed toward DNA replication

Helps prevent progression when conditions are unsuitable

What is the purpose of the S checkpoint?

Monitors DNA replication

Helps detect replication problems and DNA damage

Can delay progression while problems are addressed

What is the purpose of the G2 checkpoint?

Helps ensure DNA replication is complete

Prevents entry into mitosis when DNA damage or replication problems remain

What are cyclins?

Regulatory proteins that control progression through the cell cycle

Their concentrations and activity change during different phases

Bind to and help activate CDKs

What are cyclin-dependent kinases?

Enzymes that regulate cell cycle progression

Become active through interactions with cyclins

Phosphorylate target proteins, changing their activity

How do cyclins and CDKs work together?

Cyclins bind to specific CDKs to form regulatory complexes

These complexes phosphorylate proteins involved in cell cycle progression

Different cyclin-CDK combinations regulate different stages

What is the role of Cyclin D and CDK4/6?

Cyclin D binds to CDK4 or CDK6

These complexes regulate progression though G1

They phosphorylate RB1, helping cells progress toward DNA replication

What is RB1?

Is a tumor suppressor

Why is RB1 important?

Helps prevent inappropriate cell cycle progression

Disruption of RB1 function can contribute to cancer

How does phosphorylation of RB1 affect the cell cycle?

Cyclin D-CDK4/6 complexes phosphorylate RB1

This reduces RB1’s restraint on cell cycle progression

Helps cells advance toward the G1-to-S transition

What is the role of Cyclin E and CDK2

Regulates the G1-to-S transition

Helps initiate DNA replication

Acts after earlier G1 regulatory events

What is the role of Cyclin A and CDK2?

Associated with S phase

Helps regulate DNA replication and progression through the cell cycle

What is the role of Cyclin A and CDK1?

Associated with G2 progression

Helps regulate events leading toward mitosis

What is the role of Cyclin B and CDK1?

Helps trigger entry into mitosis

Regulates events required for mitotic division

What is the G0 phase?

A nondividing state outside the active cell cycle

Cells may remain in G0 temporarily or for extended periods

Some cells enter G0 as they become specialized

How is G0 related to cellular differentiation?

Differentiating cells may exit the active cell cycle and enter G0

This allows cells to focus on specialized functions instead of continued division

What cyclin-CDK combination does the lecture associate with G0?

Cyclin C-CDK3

The lecture associates this combination with G0 regulation

Temporary Exit

Cell stops dividing but may reenter the active cycle

Terminal Differentiation

Cell becomes highly specialized and irreversibly exits the cell cycle

What are three examples of terminally differentiated cells?

Neurons: Specialized for transmitting signals

Skeletal muscle fibers: specialized for contraction and movement

Cardiomyocytes: Heart muscle cells specialized for contraction

How is cancer related to cell cycle regulation?

Cancer can develop when normal cell cycle controls become disrupted

Cells may continue dividing when they should stop

Abnormal regulation can involve cyclins, CDKs, and tumor suppressors

Why is RB1 considered a tumor suppressor?

RB1 helps restrict inappropriate progression through the cell cycle

Loss of RB1 function can allow abnormal cell division

This contributes to the development of certain cancers

What are polytene chromosomes?

Giant chromosomes containing many aligned copies of DNA

Form through repeated DNA replication without normal cell division

Found in fruit fly salivary glands

Can contain approximately 1000 chromosome copies

What is S-looping?

Repeated cycling through DNA synthesis without completing normal mitosis and cytokinesis

Produces additional DNA copies

Can lead to the formation of polytene chromosomes

How do cell cycles vary among different organisms?

Prokaryotes: B-C-D cycle

Eukaryotes: G1-S-G2-M cycle

Some eukaryotic cells enter G0 or undergo differentiation

Cell cycle activity varies with organism and cell type

What biological changes are associated with cellular aging?

Telomere shortening: loss of procetive chromosome-end DNA

DNA damage: accumulation of genetic damage

Metabolic changes: alterations in cellular processes

These changes can affect cell function and division

How are differentiation, terminal differentiation, and cellular aging related?

Differenaition: Cells develop specialized functions

Terminal differentiation: cells become specialized and permanently exit the cell cycle

Cellular aging: changes accumulate over time and can affect cell function

All influence how cells function and whether they continue dividing

What is ploidy?

The number of complete chromosome sets within a cell

Haploid, diploid, tetraploid, etc.

What does haploid (N) mean?

A cell containing one complete set of chromosomes

Contains one copy of each chromosome type

What does diploid (2N) mean?

A cell containing two complete sets of chromosomes

Typically cintains one set inherited from each parent

What are homologous chromosomes?

Chromosomes that carry corresponding genes at the same locations

Typically one homolog is inherited from each parent

How many unique chromosome types do humans have?

23

Does having more chromosomes mean an organism is more complex?

No

What chromosome count does the lecture give for alder’s tongue fern?

720

What is a major advantage of haploidy?

Harmful and beneficial alleles are directly exposed to natural selection

Recessive alleles cannot be masked by a second allele

Why can natural selection act rapidly in haploid organisms?

They have only one allele for each single-copy gene

harmful recessive alleles are expressed rather than hidden

What is a major disadvantage of haploidy?

No second allele is available to mask harmful recessive mutations

Limited heterozygosity at single-copy genes

What are two major advantages of diploidy?

Genetic redundancy and preserved genetic variation