D2 Regulation of Cellular Processes

cell proliferation

process by which a cell grows and divides to produce two daughter cells

examples: embryological development, plant meristems, tissue replacement and healing

cell cycle

cells proliferate throughout the cell cycle, which includes:

• interphase

  • G1 phase: cell grows, protein synthesis occurs

  • S phase: DNA replication occurs to produce chromosomes

  • G2 phase: cell prepares for mitosis by growing and replicating organelles

• mitosis

• cytokinesis

cyclin

proteins that regulate the cell cycle through the binding to a cyclin-dependent kinase

• starts a reaction cascade, targeting proteins to drive the cell from one phase to the next

cyclin-dependent kinase

type of enzyme that cyclins bind to to start a reaction cascade to regulate the cell cycle

tumor initation

when a cell loses control of its cell cycle, through mutagens or random/inherited mutations

tumor suppressor gene

genes that make the cell cycle stop

proto-oncogenes

genes that make the cell cycle go (ex. cyclins)

mutations to this can make it become an oncogene

oncogenes

mutated gene that causes continuous and uncontrolled cell division (can lead to cancer)

tumor

caused by abnormal cell growth, due to mutation of tumor suppressor genes and proto-oncogenes

two types:

• benign - non cancerous, grow slowly, do not undergo metastasis

• malignant - cancerous, grow quickly, undergo metastasis

cancer

disease caused by a malignant tumor, where cancerous cells spread via metastasis

mitotic index

= mitotic cells/total ceels

cancerous tissue will have higher MI than that without

will always be a decimal between 0 and 1

gene expression

mechanism by which genetic information in a gene is expressed as a protein

steps:

• transcription of gene to produce mRNA

• translation of mRNA by ribosomes to produce a protein

genotype

combination of alleles inherited by an organism

phenotype

observable traits of the organism (affected by genotype and environment)

RNA polymerase

enzyme that transcribes a gene into mRNA

promoter

DNA region where transcription begins by binding of RNA polymerase and transcription factors

enhancer

sequence of DNA that enhances transcription by binding activators

the DNA loops to bring it close to the promoter

activator

transcription factor regulatory protein that increases transcription

silencer

transcription factor regulatory protein that inhibits transcription

transcription factor

proteins that bind to enhancer and promoter regions to regulate transcription.

• silencers and activators

nuclease

enzyme that breaks down/degrades mRNA

post transcriptional modifications to mRNA

• addition of a 5’ cap

• addition of a 3’ poly-A tail

• splicing (removal of introns and joining of exons)

these are done for efficiency in translation and to protect mRNA from nucleases during export out of nucleus

(mRNA with shorter poly-A tails are less likely to be translated bc they are more susceptible to nuclease degradation)

intron

non coding sequence of RNA

removed after transcription to create mature mRNA, not expressed in final RNA product

in = interfering, needs to be removed

exon

coding sequence of RNA

joined together after transcription to create mature mRNA, remains after splicing

ex = expressed

epigenesis

idea that all cells share the same genome - differentiation into specific cells happens when some genes are activated (turned on) or silenced (turned off).

epigenetics

study of changes in organisms caused by modifications of gene expression by epigenetic tags rather than changes in genetic code

(phenotype is changed, not genotype)

epigenetic tags

chemical markers/modifications that attach to DNA and histones and influence transcription by activating or silencing genes

genome

all of genetic information (base sequences) in a cell

transcriptome

all of the mRNA sequences in a cell

proteome

all of the proteins produced in a cell

methylation

• methyl groups (-cH3) act as epigenetic tags by attaching to promoter region on DNA and histones

  • on promoter: represses promoter activity, preventing gene from being transcribed

  • on histones: winds DNA tightly, preventing transcription, or can do the opposite and unwind as well

epigenome

all epigenetic tags on DNA and histones

affected by environmental factors like diet, smoking/pollution, exercise

epigenetic inheritance

• epigenome (epigenetic tags) often remain during mitosis/meiosis, daughter cells inherit it along with genome of parent cells

• most, but not all, epigenetic tags are erased at fertilization (reprogramming) and unable to be passed on

  • previous hypothesis was that epigenetic tags were cleared during meiosis

genomic imprinting

when epigenetic tags remain on DNA during gamete formation and passed onto offspring

• tigons and ligers - ligers are large because the growth promoting genes in male lions, tigers have no growth repressing genes like female lions do

monozygotic twins

identical twins resulting from fertilization of one egg, with the same genome, and initially similar epigenomes

lac operon

• e coli bacteria’s lac operon controls when it makes enzymes to digest lactose

when lactose is absent

• repressor protein binds to operator, physically blocking RNA polymerase from moving along the DNA

• no mRNA, and hence enzymes, can be made

when lactose is present

• lactose binds to the repressor protein, changing its shape so it detaches from the operator

• RNA polymerase can now transcribe the three genes into mRNA, creating enzymes that digest the lactose

lac operon structure

• promoter: region where RNA polymerase attaches to start transcription

• operator: on/off swtich where a repressor protein can bind to stop transcription

• three genes: code for enzymes needed to break down lactose

testosterone’s affect on gene expression

steps:

1. testosterone diffuses thru membrane of the cell, where it binds to a testosterone receptor

2. the hormone receptor complex moves to the nucleus, where it interacts with specific DNA sequences (androgen response elements)

3. the complex may enhance or repress transcription of target genes

water potential

• potential energy of water per unit volume, relative to pure water

• measured in kPa, pure water at 20C is 0 kPa

• determines how freely water particles can move in a solution

what is water potential affected by?

two things:

• pressure: increase in pressure = increase in water potential (positive relationship)

• solute concentration: increase in conc = decrease in water potential (inverse relationship)

water potential formula

solute potential + pressure potential

• Solute potential: adding solutes decreases water's ability to move freely. always negative

  • High solute concentration = Low (more negative) solute potential.

• Pressure potential: pressure exerted on the water. usually positive inside a turgid plant cell, though it can be negative like in xylem vessels under tension.

effect of pressure on cells

• Positive pressure potential causes a cell to swell (become turgid)

• Negative pressure causes it to shrivel (plasmolyze).

hypertonic

• solute concentration outside is higher than inside

• water goes out of the cell

• cell shrivels

hypotonic

• solute concentration is higher inside than outside

• water rushes into the cell

• cell swells like a big fat hippo (only animal cells burst, plant cells have cell walls to prevent this)

movement of water

directions of flow:

• high water potential → low water potential

• low solute concentration → high solute concentration

• high pressure → low pressure