Exam 3 review

The plasma membrane plays a key role in cell signaling. Communication between cells involves:

1. A signaling cell that produces the signaling molecule, also called a ____

2. A responding cell that contains the specific ______ for the signaling molecule

ligand, receptor

What is Local Signaling

cells communicating over short distances

Direct Cell contact:

Animal and plant cells have cell junctions that directly connect the cytoplasm of adjacent cells.

Animal cell junctions

Gap Junctions

Plant cell junctions

Plasmodesmata

Direct cell contact is important during…..

embryonic development

immune response

maintaining adult stem cell populations

Paracrine Signaling

Animal cells communicate using secreted messenger molecules that travel only short distances

Growth factors, which stimulate nearby target cells to grow and divide, are one class of such local regulators in animals

Synaptic signaling

• Occurs in the animal nervous system when a neurotransmitter is released in response to an electrical signal

• Drugs used to treat depression, anxiety, and post-traumatic stress disorder (P T S D) affect this signaling process

Harmonal/ Endocrine signaling

1. In long-distance signaling, plants and animals use molecules called hormones 

2. In this signaling in animals, specialized cells release hormones, which travel to target cells via the circulatory system 

3. The ability of a cell to respond to a signal depends on whether or not it has a receptor specific to that signal 

4. Essentially, hormones -> long distance -> receive the hormones through a receptor

What are 3 stages of Cell Communication

reception, transduction,and cellular response

Reception

:

A signal molecule (ligand) binds to a specific receptor and causes a change in the receptor and activates it

Transduction

:

Like falling dominoes, the receptor activates another protein, which activates another, and so on, until the protein producing the response is activated

Cellular Response:

The signal finally triggers a specific cellular response

• Activation of an enzyme

• Activation of genes to turn on (or off) expression of a protein (gene regulation)

• Rearrangement of the cytoskeleton

Are receptors always located on the plasma membrane?

No, they are intracellular receptors and cell surface receptors

G protein-coupled receptors (GPCRs)

a plasma membrane receptor that works with the help of a G protein

Receptor tyrosine kinases (RTKs)

Membrane receptors that catalyze the transfer of phosphate groups from ATP to another protein

Ion channel receptor

• They're important for the functioning of our nervous system

• When a ligand binds to a Ligand-gated ion channel receptor, the receptor changes shape, opening a gate. 

• The gate in the receptor allows specific ions, such as Na+ or Ca2+, to pass through the channel in the receptor

Protein kinases

transfer phosphate groups from ATP to proteins, a process called phosphorylation.

• 
  

Phosphatases

Enzymes that remove a phosphate group from a protein (a process called dephosphorylation). This reverts the protein to its original shape, deactivating it and turning it "off".

Name two "second messengers" commonly used in cellular signaling pathways

Cyclic AMP (cAMP) and Calcium ions (Ca2+)

What are two broad ways that a cell can respond to a signaling pathway?

• Regulation of Gene expression: Turns proteins on or off

• Cytoplasmic Activities: Regulates the activity of enzymes already synthesized by the cell

What are the 5 main mechanisms a cell uses to terminate a signaling pathway response?

• Reversible Ligand Binding (Ligand Dissociation):

  • Ligand binding is non-covalent and reversible. As extracellular ligand levels decrease, ligands detach, reverting the receptor to its inactive shape.

• GTP Hydrolysis (Intrinsic GTPase Activity):

  • Activated G proteins use built-in GTPase activity to hydrolyze GTP back to GDP, turning the G protein "off" and halting downstream stimulation.

• Dephosphorylation by Protein Phosphatases:

  • Phosphatases rapidly remove phosphate groups from active kinases and target proteins, shutting off the phosphorylation cascade.

• Breakdown / Removal of Second Messengers:

  • cAMP: The enzyme phosphodiesterase degrades active cAMP into inactive AMP.

  • Ca²⁺: Active transport pumps immediately pump Ca²⁺ out of the cytosol (back into the ER or outside the cell).

• Receptor Desensitization & Internalization:

  • Prolonged exposure leads to receptor phosphorylation/blocking (e.g., arrestin binding) or removal from the plasma membrane via endocytosis (sequestration or lysosomal destruction).

Apoptosis

• Components of the cell are chopped up and packaged into vesicles that are digested by scavenger cells 

• Apoptosis prevents enzymes from leaking out of a dying cell and damaging neighboring cells

If a ligand is water-soluble, where is the likely location of its receptor?

On the plasma membrane

 If a ligand is hydrophobic, where is the likely location of its receptor?

Within the cell intracellular / through the plasma membrame

If a ligand is released directly into the bloodstream, why does every cell in the body not respond to it?

Because it only reacts to a specific receptor. Only target cells with the specific complementary receptor for that hormone can bind it and trigger a response. Cells lacking the receptor ignore the signal entirely.

Which class of receptors is highly important for taste, vision, and smell?

GPCR

 Which class of receptor functions directly as an enzyme?

Receptor Tyrosine Kinases (RTKs).

Which class of receptors undergoes dimerization upon ligand binding?

RTK

 Which class of receptors is essential for muscle contraction?

 Ion channel

 Which class of receptors is essential for nerve cell function?

Ligand-gated ion channels (and voltage-gated ion channels).

 Which class of receptors directly utilizes ion flow into a cell?

Ligand-gated ion channels

Explain how a signaling molecule can produce a cellular response when it does not physically enter the target cell?

Because the receptor is able to pick up on the signal molecule and, through transduction that happens in the cell, it can produce a cellular response

More detailed: The ligand binds to an extracellular receptor, causing a conformational (shape) change in the receptor protein. This structural shift transmits the signal across the plasma membrane into the interior of the cell, initiating a signal transduction pathway (often involving second messengers or phosphorylation cascades) that relays and amplifies the message to trigger the final cellular response.

Chromatin

The uncondensed of a chromosome

Chromosome

Genetic material that is packaged in the nucleus / long, discrete units of organized DNA.

Chromatid

One of the two identical halves of a duplicated chromosome

Centromere

Where the two chromatids are most closely attached 

Mitosis

This is the process of nuclear division in eukaryotic cells where duplicated chromosomes are evenly divided, resulting in two genetically identical nuclei.

What are the major stages of the cell cycle?

Interphase ( G1, S, G2)

Mitotic Phase ( mitosis and Cytokinesis)

Whats happens during Interphase

Cell growth and copying of chromosomes in preparation for cell division

DNA replication occurs here, more specifically S phase

What is the mitotic phase?

1. During the phase, the two sister chromatids of each duplicated chromosome separate and move into two nuclei 

2. Once separate, the chromatids are called chromosomes again

4 main stages of mitosis

prophase, metaphase, anaphase, telophase

Prophase ( + prometaphase)

Chromosomes start to condense and are coiled into discrete chromosomes consisting of two sister chromatids.

The nucleoli disappear.

The mitotic spindle begins to form

The centrosomes move away from each other

The nuclear membrane breaks down - pm

The microtubules extending from each centrosome can now invade the nuclear area

Spindle microtubules attach to the chromosome kinetochore - pm

Metaphase

The longest phase of mitosis.

Chromosomes are fully condensed and most visible at this stage

The sister chromatids are arranged at the metaphase plate, or the equator of the cell, an imaginary plane, equidistant from the spindle’s two poles

Anaphase

The sister chromatids separate and become full-fledged chromosomes

Each freed chromatid (now referred to as a chromosome or daughter chromosome) is pulled toward the opposite pole of the cell

Telophase

• The two sets of chromosomes have reached the opposite poles of the cell 

• The chromosomes decondense. 

• The mitotic spindle disappears 

• Two daughter nuclei begin to form, one at each pole 

• The nuclear envelope and nucleolus reappear

Cytokinesis

The physical division of the cytoplasm and cell membrane, occurring immediately at the end of mitosis (usually beginning during late anaphase or telophase). It physically splits one parent cell into two distinct daughter cells, each with its own nucleus and share of organelles.

In animal cells, cytokinesis involves the formation of a ____ ____, which contracts to pinch the cell in two.

cleavage furrow

In plant cells, small vesicles containing cell wall materials fuse to form a ___ ___, which grows outwards to complete the formation of two daughter cells.

cell plate

What is binary fission, and in which types of organisms does it occur?

The primary method of asexual reproduction used by prokaryotes (bacteria and archaea). In this process, a single cell duplicates its genetic material and divides into two genetically identical daughter cells.

The cell cycle has specific _______ where the cell cycle stops until a go-ahead signal is received

checkpoints

What is the G1 checkpoint?

The most crucial checkpoint in most cells. It checks for cell size, nutrient availability, DNA damage, and growth factor signals.

If the cell gets the "go-ahead" signal, it commits to DNA replication (S phase) and typically finishes the whole cycle. If it does not receive the go-ahead, it exits the cycle into G₀ phase—a non-dividing, quiescent state (e.g., mature nerve and muscle cells).

What is the G2 checkpoint?

Role: Checks that DNA replication in S phase was completed accurately without damage, and confirms the cell is large enough to divide.

Outcome: Passing this checkpoint triggers the cell to enter the M phase (mitosis).

What is the M checkpoint?

• Role: Occurs at metaphase. It ensures that the kinetochores of all sister chromatids are properly attached to spindle microtubules at the metaphase plate.

• Outcome: Prevents unequal chromosome separation (nondisjunction). Only when every kinetochore is firmly attached does the cell release the signal to cleave cohesins and proceed to anaphase.

Growth Factors

Specific extracellular protein signals released by other cells that stimulate a target cell to divide.

• Density-Dependent Inhibition 

• Role: A physical phenomenon where crowded cells stop dividing.

Anchorage Dependence

Role: Most normal animal cells must be anchored to a solid substratum (such as the extracellular matrix of a tissue or a culture dish) to divide

Cyclin-Dependent Kinases (CDKs):

Enzymes that activate or inactivate other proteins by phosphorylating them.

Cyclins

:

Regulatory proteins whose concentrations fluctuate ("cycle") rhythmically throughout the cycle—synthesized during specific phases and rapidly degraded after.

Cancer cells

• They may make their own growth factor

• They may activate the growth factor’s signaling pathway without the presence of the growth factor 

• They may have an abnormal cell cycle control system 

Tumor:

A mass of abnormal cells within otherwise normal tissue

Malignant Tumor

The abnormal cells invade and impair surrounding tissues and organs. An individual with a malignant tumor is said to have cancer.

Metastasis:

The spread of cancer cells from their primary site of origin to distant locations in the body.

Meiosis

A specialized type of cell division in sexually reproducing eukaryotes that reduces the chromosome number by half.

Importance of meiosis

To reduce the chromosome number by half (from diploid to haploid) and produce genetically unique gametes (sperm and egg cells) for sexual reproduction

Fertilization:

The physical union of two haploid gametes (a sperm and an ovum), culminating in the fusion of their nuclei.

Zygote

The single-celled, diploid (2n) fertilized egg produced immediately after fertilization occurs.

Karyotype:

An organized visual display of an individual’s complete set of condensed chromosomes, arranged in homologous pairs and ordered by size, centromere position, and banding pattern.

Homologous chromosomes

A pair of chromosomes, one inherited from each parent, maternal & paternal

Are very similar to each other—same size, carrying the same genes in the same order

But are not identical due to individual mutations (different alleles)

Duplicated chromosomes

single chromosomes that have copied their DNA during the S phase, consisting of two identical sister chromatids joined at a centromere.

Ploidy: What is the difference between diploid (2n) and haploid (n) cells

Cells containing two complete sets of chromosomes—one maternal set and one paternal set. Chromosomes exist as matched homologous pairs.

And the other: Cells containing only one single set of chromosomes (no homologous pairs; only one chromosome from each pair)

Autosomes are the first 22 pairs that determine characteristics other than sex

Homologous pairs

Sex Chromosomes

the 23rd pair that determines sex. Non-homologous pair

Somatic Cells:

• Are all the body cells except for the gametes

• Are diploid (2n), have two sets of chromosomes 

• Human somatic cells have 23 pairs of homologous chromosomes (46 chromosomes). 

  • - 22 pairs of autosomes (44 chromosomes) 

  • 1 “pair” of sx chromosomes (2 chromosomes) 

    • XX or XY 

• Female somatic cells: 44 autosomes & XX

• Male somatic cells: 44 autosomes & XY

Gametes

• The egg (ovum) and sperm 

• Are haploid (n), have one set of chromosomes

• Human gametes have 23 chromosomes 

  • 22 autosomes

  • 1 sex chromosome

    • X or Y

• Female eggs: 22 autosomes & X

• Male sperm: 22 autosomes & X OR 22 autosomes & Y

In __________ __________, a single individual passes all of its genes to its offspring without the fusion of gametes

asexual reproduction

In __________ ______________ two parents give rise to offspring that have unique combinations of genes inherited from the two parents

sexual reproduction,

Independent Assortment of Chromosomes

Homologous pairs of chromosomes orient randomly at metaphase I of meiosis

Crossing Over

1. Occurs during prophase 1 produces recombinant chromosomes, which combine DNA inherited from each parent 

2. In humans, on average, one to three crossover events occur per chromosome pair 

3. Contributes to genetic variation by combining DNA 

4. Produces new chromosome combinations with maternal and paternal alleles 

5. Thus, each zygote has a unique genetic identity

Random Fertilization

This adds to genetic variation

Because any sperm can fuse with any egg

The fusion of two gametes (each with >8.4 million possible chromosome combinations from independent assortment) produces a zygote with any of about 70 trillion diploid combinations!!!!

• Meiosis consists of ___ consecutive cell divisions, resulting in the formation of ___ daughter cells.

two, four

Each daughter cell contains ____ the number of chromosomes as the parent cell.

half

he daughter cells are all _________. The primary reasons for this variation are synapsis and crossing over (chiasmata), which take place only in meiosis during ________I.

different from one another, prophase I.

Meiosis produces _____ - called gametes - eggs in females, sperm in males.

sex cells

During Meiosis I _________separate.

During Meiosis II, ________- separate.

homologous chromosomes, sister chromatids

How many total chromosomes are in a human intestinal cell?

How many autosomes are in a human intestinal cell? 44 (22 pairs)

46 (arranged in 23 pairs), 44

How many sex chromosomes are in a human intestinal cell?

2 (1 pair, XX or XY)

Is a human intestinal cell haploid or diploid?

Does it contain homologous chromosomes?

• Diploid (2n=46)

• Yes (each of the 23 pairs consists of two homologous chromosomes, one inherited from each parent)

What type of cell division produces a human intestinal cell?

Mitosis

• How many total chromosomes are in a human gamete (egg or sperm)?

• How many autosomes are in a human gamete?

23 then 22

• How many sex chromosomes are in a human gamete? (either an X or a Y)

• Is a human gamete haploid or diploid?

1 then haploid

• Does a gamete contain homologous chromosomes?

  • If not, why not?

NO, Homologous pairs are separated during meiosis I, leaving only one chromosome from each pair in the resulting haploid gametes.

What type of cell division produces a human gamete? 

Meiosis

Compare Mitosis vs. Meiosis across the following 5 key features:

• Number of cell divisions

• Number of daughter cells produced

• Primary function in the body

• Genetically identical to parent? (Yes/No)

• Ploidy of daughter cells (Haploid or Diploid)

Feature	Mitosis	Meiosis
Number of Cell Divisions	1	2
Number of Daughter Cells	2	4
Primary Function in Body	Growth and tissue repair	Production of gametes (sex cells)
Genetically Identical to Parent?	Yes	No (genetically diverse)
Ploidy of Daughter Cells	Diploid (2n)	Haploid $n)

Which type of cell division produces gametes? __________________

 Which type of cell division results in daughter cells with 46 chromosomes? __________________

 Which type of cell division is involved in growth & repair in the body? __________________

 Which cell division results in cells with half the amount of DNA as the parent cell? __________________

Meiosis, mitosis, mitosis, meiosis

Feature	Human Somatic Cell	Human Gamete
Examples in the body
Total # of chromosomes
# Of Autosomes/ Autosomes pairs
# of Sex Chromosomes
Contains Homologous Chromosomes
Ploidy level (Haploid or diploid)
Number of Chromosomes Sets ( One or two?)
Produced by which division? Mitosis or meiosis)

Feature	Human Somatic Cell	Human Gamete
Examples in the body	Nerve Cells	Sperm
Total # of chromosomes	46	23
# Of Autosomes/ Autosomes pairs	44 autosomes (22 pairs)	22 autosomes (unpaired)
# of Sex Chromosomes	2	1
Contains Homologous Chromosomes	yes	no
Ploidy level (Haploid or diploid)	Diploid	Haploid
Number of Chromosomes Sets ( One or two?)	2	1
Produced by which division? Mitosis or meiosis)	Mitosis	Meiosis

Gregor Mendel: Why is Gregor Mendel famous, and what plant did he work with to discover the basic principles of heredity?

He discovered the basic principles of heredity, and he worked with the common pea plant (Pisum sativum).

1. What is the male part of a pea plant called _____

2. What is the female part of a pea plant called ______

3. What is the male gamete in a pea plant called ______

Starmen, carpel, pollen

Gene

A discrete unit of hereditary information consisting of a specific nucleotide sequence in DNA that codes for a functional protein or RNA molecule. Units of Inheritance

1. Example: The gene for plant height in pea plants.

Allele

Alternative forms (specific variants) of the gene that account for variations in inherited characters.

Example: The tall allele (T) versus the dwarf allele (t).