BIOL exam 4 objectives

Signal Transduction

Cascades of molecular interactions transmit signals from receptors to relay molecules in the cell

Cellular response

Cell signalling leads to cytoplasmic activities or regulation of transcription

Signal Reception

A signalling molecule binds to a receptor protein, causing it to change shape (specific, induced fit interaction)

Juxtacrine signalling

Via direct cell-to-cell binding / recognition: 7 • e.g., during fertilization, sperm binds to complementary receptors on egg surface • Immune cell function: self/non-self recognition, removal of pathogens by phagocytosis

Autocrine signalling

a cell targets itself: ex. • Cancer cells hijack this system and produce their own growth factors • Liver regeneration • Immune T cell expansion

paracrine signalling

a cell targets a nearby cell. Local secreted regulators that travel only short distances • E.g., growth hormones • Synaptic signalling

endocrine signalling

in animals, a cell targets distant cells through the blood stream. e.g., adrenaline secreted by adrenal glands located just above kidneys following signal from the brain => => fight-or-flight response: faster heartbeat & breathing alertness, slowed digestion

long distance signalling

• Uses chemicals called hormones • In plants - long-distance transport or long-range signalling • In animals - endocrine signalling

the presence of a specific receptor (lock and key)

Ability of a cell to respond depends on

intracellular relay proteins

Type of cell response depends on:

plasma membrane proteins (cell-surface receptors)

Most signal receptors are:

three main types of membrane receptors

1. G protein-coupled receptors (GPCRs) 2. Receptor tyrosine kinases 3. Ion channel receptors

GPCR

a plasma membrane receptor that works with a G protein. The largest family of cell-surface receptors

G protein

acts as an on/off switch

GPCR’s: rhodopsin and green-, red-, blue-light photopsins in the eye

abnormalities in these are associated with blindness, colour blindness

abnormalities with GPCR’s

neurodegenerative diseases, thyroid disorders, obesity, diabetes, phsychiatric conditions.

inactive

If GDP is bound to G protein, it is

active

If GTP is bound to G protein, it is

Receptor tyrosine kinases (RTKs)

Phosphorylate (i.e., attach phosphates to) tyrosines • Can trigger multiple signal transduction pathways (58 RTKs in humans, in 20 families) • Abnormal function associated with many cancers

Ion channel receptors (aka ligand-gated ion channels)

Act as gates: – ligand = closed + ligand = open, allows specific ions, e.g., Na+ or Ca2+, through the channel • Function in, e.g., neurons • Mutations lead to various diseases, e.g., epilepsy

Intracellular receptors

• In the cytosol or nucleus of target cells • Bind small or hydrophobic chemical messengers (signalling molecules, e.g., steroid and thyroid hormones) that can readily cross the membrane

Enzyme cascades

amplify the cell’s response

signal amplification

At each step, the number of activated products is much greater than in the preceding step

second messengers

Small, non-protein water-soluble molecules or ions that spread throughout the cell by diffusion (may spread to adjacent cells through gap junctions) Cyclic AMP (cAMP) and calcium ions (Ca2+)are common

Adenylyl cyclase

an enzyme in the plasma membrane, converts ATP to cAMP in response to an extracellular signal

Phosphodiesterase

breaks down cAMP to AMP

cytoplasmic responses

Regulate the activity of existing molecules (no gene expression regulation is involved). E.g.: – Opening or closing of an ion channel. – Epinephrine stimulates glycogen breakdown in liver cell

nuclear responses

Final activated molecule in the signalling pathway is a transcription factor • Ultimately turn gene expression on or off

karyotype

Arranging the chromosomes by size when chromosomes are most condensed produces a

homologous

Chromosomes (homologs) that pair in reproduction of diploid cells are described as

heterologous pairs

Some genomes have pairs that don’t match, for example X and Y chromosomes in humans.

centromere

is the constriction that can be seen in the duplicated chromosome, where sister chromatids are most closely attached

chromosomes

Once they have been separated, the sister chromatids are called

cytokenesis

the division of the cytoplasm

mitosis

the division of the genetic material in the nucleus of Eukaryotes

meiosis

Gametes produced by a variation of cell division called ______, which yields non-identical daughter cells that have half as many chromosomes as the parent cell

Karyokinesis

nuclear division, the first step of mitotic phase

cytokinesis

The second portion of the mitotic phase, called cytokinesis, is when the cytoplasmic components physically separate into 2 daughter cells

mitotic spindle

The _________________ is made of microtubules that control chromosome movement during mitosis

centrosome

• In animal cells, assembly of spindle microtubules begins in __________, the microtubule organizing centre

interphase

• The centrosome replicates during ___________; the two resulting centrosomes migrate to opposite ends of the cell during prophase and prometaphase

Kinetochores

are protein complexes that form in association with the centromeres of chromosomes

prometaphase

• During _________, some spindle microtubules attach to kinetochores and begin to move chromosomes

metaphase plate

At metaphase, chromosomes line up at the ____________ (the midway point between the two spindle poles)

telophase

In _______ genetically identical daughter nuclei form at opposite ends of cell

Cytokinesis begins

_____________ during anaphase or telophase

Prophase

beginning of mitosis • Nuclear envelope breaks down • Membranous organelles disperse toward edges of the cell • The nucleolus disappears • Centrosomes begin migration to poles • Microtubules of the spindle form • Sister chromatids coil tighter (aided by condensin proteins)

Prometaphase

Sister chromatids develop a protein kinetochore in the centromere region which attaches the chromatids to the spindle microtubules

Metaphase

• Chromosomes line up along metaphase plate • Sister chromatids remain attached by cohesion proteins

Anaphase

• Cohesin proteins degenerate allowing chromatids to separate • Separated sister chromatids move in opposite directions toward the centrosomes to which their microtubules are attached • The cell elongates

telophase

• Chromosomes reach opposite poles and begin to decondense (unravel) • Spindles depolymerize into tubulin monomers that will form cytoskeletal components for the daughter cells • Nuclear envelopes form around the chromosomes

Apoptosis

is programmed cell death

Negative Regulators

stop advancement of the cell cycle

Positive Regulators

promote movement to next step of the cell cycle. include cyclins (proteins) and cyclin-dependent kinases (Cdks). • Kinases are enzymes that phosphorylate proteins.

Proto-oncogenes

are normal genes that code for positive cell cycle regulators

Meiosis I

(reductional division, 2n to n): homologous chromosomes separate

Meiosis II

(equational division, started with n and end with n): sister chromatids separate

gametophytes

The haploid multicellular plants are called ___________, because they produce gametes from specialized cell

Dichotomous traits

characteristics with only two distinct, opposite possibilities, like a pea plant being either tall or short, or a seed being round or wrinkled, forming a simple "either/or" division

trait

characteristic like flower color, eye color etc.

Phenotype

the characteristic version of a trait we actually see. Example: purple flower or blue eyes

Alleles

specific versions of a “hereditary particle” (today= versions of a gene)

Dominant

alleles that mask others – often designated with capital letters. Example: P for purple flower

Recessive

alleles that are masked by others – often designated with lower case letters Example p for white flower

Genotype

the specific combination of “hereditary particles” carried by an individual that cause a phenotype

Homozygote

when both alleles for the same trait are the same. Example: PP or pp (Note – homozygotes are always true breeding)

Heterozygote

when alleles for the same trait differ. Example Pp (Note – heterozygotes are always non-true breeding)

Zygote

first diploid cell produced by fertilization

Gene

place in the DNA strand that encodes information causing a trait. (Mendel’s “hereditary particles”)

Locus

place of interest on a chromosome, usually a gene

Reciprocal cross

A formal mating cross where a previous cross is repeated, but the parents exhibiting versions of a phenotypic trait are reversed by sex

Wildtype allele

the most common allele in a population (so called “normal allele”)

Mutant allele

A rare allele in a population. Reasoned to be the most recently formed allele by mutation (so called “nonnormal allele”)

monohybrid cross

Punnett Square for a ____________ cross has 4 squares

dihybrid cross

Looking at two characters is a __________ cross. à Punnett Square can come in handy; -16 squares

trihybrid cross

Three characters is a _________ cross. à Punnett Square is necessary but is also complicated; -64 squares

not functional

one allele has an effect on phenotype. Why? the protein produced via transcription and translation of the recessive allele is _______

no functional protein being produced

The recessive phenotype becomes visible only in the homozygous recessive condition, i.e. in the situation where there is _________ from a particular gene

Polygenic inheritance

describes traits controlled by multiple genes, not just one, leading to a wide range of phenotypes (like height, skin, or eye color) rather than distinct categories

Pleiotropic genes

One gene that influences multiple phenotypic traits. • E.g., product of a gene is used in more than one cell type. • _____________ are often identified due to multiple phenotypic effects of rare (often recessive) alleles.

Epistasis

When one gene alters or modifies the effects of another gene. well-known examples involving mammal fur colour.

autosomal dominant

not all genetic disorders are caused by recessive alleles. for some, one copy of the allele is sufficient to exhibit the disorder

X-linked

• _________ disorders tend to be more common in males than females. • If males have one copy of the recessive allele —) exhibit the disorder. • Females must have two copies of the recessive allele to exhibit the disorder.

common x linked disorders

red-green colour blindness, two forms of muscular dystrophy (loss of muscle mass), two forms of hemophilia (blood fails to clot)

lethal

Technically, an allele only has to shorten the average normal life span to be considered

1) independent assortment of chromosomes 2) crossing over 3) random mating

Sexual reproduction leads to new allele combinations (shuffling the genetic deck) via:

mutations

may be caused by DNA copying errors

translocations

(chunk of a chromosome joins with a different chromosome) leading to cancer

chromosome fusion

a group of genes that occur on two separate chromosomes in chimps are together in one chromosome in humans

chromosome inversion

Large chunks of chromosomes flipped 180° and then re-inserted

Whole Genome Duplication (WGD)

• Seems to have been very important in the evolution of some plant groups. • These are an accident of meiosis. • When they happen, they double the number of genes

somatic

Mutations in _______ cells, while they do indeed occur, are not passed on to offspring. However can potentially lead to cancer.

Mendel's law of segregation

Each individual has two alleles for each gene, and these alleles separate during gamete formation so that each gamete receives only one allele

+

means wild type or nonmutant type