Unit 5: Lesson 7 Flashcards
apoptosis
- programmed cell death
- cell shrinks, cell parts are packaged into vesicles which are engulfed and digested by scavenger cells
Apoptosis in embryonic development; C.elegans
-a death cell inactivates Ced-9 allowing Ced-4 and Ced-3 to activate, leading to activation of other proteases and nucleases (enzymes that cause the changes seen in apoptosis)
Initiating Apoptosis
- mitochondrial proteins triggered to from pores which cause leakage and release of apoptosis promoting proteins
- death ligand binds to surface receptor, leading to activation of capases (enzymes which carry out apoptosis)
- damaged nucleus or misfolded ER can also send death signal
Apoptosis is essential for:
normal development of vertebral nervous systems, operation of immune system, normal morphogenesis
histone acetylation
neutralizes histones so they do not bind to neighbors. Results in looser structure and easier access to genes
-enzymes involved may also bind to and recruit components of transcription machinery
histone methylation
- promotes condensation of chromosomes
- phosphate next to methyl causes loosening
epigenetic inheritance
inheritance of traits transmitted by mechanisms not directly involving the nucleotide sequence
Eukaryotic Gene transcription
- transcription initiation complex (proteins, RNA polymerase II) assembles on promoter
- RNA polymerase II synthesizes pre-RNA
- RNA processing: adds 5’ cap and 3’ tail, introns removed
General transcription factors
bind to DNA or other proteins, forming an initiation complex that produces a low level of transcription
Specific Transcription factors
- can greatly increase or decrease rate of gene expression by binding to the distal control elements of the enhancer
- can also recruit proteins that acetylate or deacetylate histones
activators
- Bind to control element
- DNA bends bringing activators closer to the promoter
- bind to mediator proteins and general transcription factors, helping form a transcription initiation complex on promoter
repressors
-can bind to control element or block binding of activators to proteins that let activators bind to DNA
Coordinately controlled genes
- dispersed but have a specific combination of control elements
- a chemical signal produces/activates a particular transcription activator or repressor
alternative RNA splicing
-depends on regulatory proteins that bind to regulatory sequences, which choose which segments are treated as exons and which as introns
mRNA degredation
lifespan of mRNA in cytoplasm (controlled by untranslated nucleotide sequences) plays a role in pattern of protein synthesis
- if short can change quickly
Initiation of translation
- regulatory proteins may bind to untranslated region of ends, preventing ribosome attachment
- in eggs, poly-A tails may be too short, but at the appropriate time Adenine nucleotides are added
- activation or inactivation of required protein factors can regulate translation of all mRNA’s simultaneously
For functional proteins
-eukaryotic polypeptides must be processed, chemical modifications must occur, must be transported to target destinations
microRNA
- small, single stranded, noncoding RNA
- forms a complex with proteins, binds to complementary mRNA, then degrades mRNA or blocks translation
small interfering RNAs
similar to microRNA but have linear precursor molecule
-can cause remodeling of chromatin structure
piwi-associated RNAs
induce heterochromatin formation by blocking expression of transposens (parasitic DNA elements)
Cytoplasmic Determinants in Cell Differentiation
RNA proteins and other maternal substances distributed randomly in egg. Division distributes zygotes to different cells, nuclei exposed to different cytoplasmic determinants
Induction in Cell Differentiation
-signals from nearby embryonic cells cause changes in gene expression in target cell
Cell differentiation
determination; early changes on molecular level that set a cell on the path to specialization
-differentiated cells are specialists at producing tissue-specific proteins, marks observable cell differentiation
Pattern formation
development of spacial organization of tissues and organs
-positional info: molecular cues that control pattern formation by telling a cell its location relative to the body axes and to neighboring cells
morphogen gradient hypothesis
gradients of substances called morphogens establish an embryo’s axes and other features of its form
Flowers
- complete containn sepals, petals, stamens, and carpels
- reproductive shoots of angiosperm sporophytes
- anther of stamen produces pollen, stigma of carpal captures pollen
Development of Male Gametophytes
diploid microsporocytes in miscrospongia split into 4 haploid microspores, which give rise to male gametophytes, which undergo mitosis
pollen grain
- consists of generative cell and tube cell centered in sporte wall
- generative cell passes into tube cell
- may be transferred to receptive surface of a stigma, tube cell produces a pollen tube which delivers the sperm to the female gametophyte
Developments of Female Gametophytes (embryo sacs)
- two integuments (sporophytic tissues) surrounds megasporangium tiuss except at micropyle
- megasporocyte enlarges and undergoes meiosis, producing 4 haploid megaspores, only one survives
- nuclei divides-resulting in a large cell with 8 haploid nuclei
- partitioned into multicellular gametophyte
Pollination
in angiosperms, the transfer of pollen from an anther to a stigma by wind, water, or animals
double fertilization process
- after landing on stigma, pollen grain absorbs water and germinates by producing a pollen tube, two sperm are formed by generative cell
- tube grows toward micropyl, attracted by synergids, and two sperm are discharged
- one sperm fertilizes the egg, other combines with polar nucli, forming a triploid nucleus
- triploid nucleus gives rise to the endosperm, a food-storing tissue of the seed
double fertilization
the union of two sperm cells with different nuclei of the female gametophyte
-ensures endosperm develops only in ovules where egg has been fertilized
Endosperm Development
- triple nucleus divides, forming a super cell with a milky consistency
- membranes formed between nuclei, produce walls, solidifying endosperm
- may be used by seedlings after germination or transfer reserves to cotyledons
Embryo Development
- Split into basal and terminal cell
- Basal cell divides producing thread of cells called the suspensor, which anchors embryo to parent plant
- Terminal cell divides, producing proembryo
- Cotyledons begin to form as small bumps on proembryo
- Embryo elongates, embryonic shoot apex and root apex form
Seed Germination and Development
imbibition (the uptake of water) causes seed to expand and rupture it coat, triggering metabolic changes
- storage materials are transferred to growing region of embryo
- radicle(embryonic root) emerges from seed, shoot tip breaks through soil surface
- light causes hypoctyl to straighten, cotyledons seperate, true leaves spread
Fruit
protects enclosed seeds and aids in their dispersal
fertilization triggers ovary to form into fruit
simple fruits
fruits derived from a single carpel or several fused carpels
aggregate fruit
results from a single flower that has many separate carpels, each forming a small fruit which are clustered together
multiple fruit
develops from an inflorescence, a group of flowers clustered tightly together
accessory fruits
develops largely from tissues other than the over
