Chp 3, Part 3, Nucleus & Cell Cycle Flashcards
nucleus
-control center of the cell, containing genes for protein synethsis of most proteins (and dictates kind and amount of proteins)
-consists of nucleur envelope, nucleoli, and chromatin
-largest organelle
-cells can by multinucleate (like muscle, bone-destruction, or liver cells)
-mature red blood cells are anucleate (no nucleus)
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nuclear envelope
- selectively permeable, double membrane barrier separated by a fluid-filled space.
- the outer membrane is continuous with the rough ER and also has ribosomes
- inner membrane is lined by the nuclear lamina
- has nucleus pores, which is lined by proteins forming an aqueous channel, regulating entry/exit of molecules (like mRNA)
nucleoli
- AKA ‘little nuclei’
- these are where ribosomal subunits are assembled and rRNA is synthesized. Then subunit+rRNA leaves through pore into cytoplasm where subunits form to make functional ribosome
Chromatin
- bumpy weaved threads in nucleoplasm made of DNA, histone proteins, and RNA (newly formed/being formed) in un-condensed form
- fundamental unit of chromatin = nucleosome (small length of DNA wrapped around histones)
chromosome
- condensed chromatin, formed when a cell is preparing to divide.
- prevent the delicate chromatin strands from tangling/breaking during the movements of cell division
nucleosome
- unit of chromatin
- made of 8 histone proteins connected like beads on a string. The DNA winds around the histones (packing the very long DNA molecules in more compact way)
Cell Cycle
- series of changes a cell undergoes from the time it is formed until it reproduces
- two major periods are interphase and mitosis (cell division)
Cell Cycle
- series of changes a cell undergoes from the time it is formed until it reproduces
- two major periods are interphase and mitosis (cell division)
Interphase
- This is the metabolic/growth phase
- split into G1, S, and G2 - during all three phases there is some growth (with most in G1) and DNA replication is in S phase (Synthetic)
mitosis / mitotic phase
- where cell division occurs
- split into Mitosis and Cytokinesis
- Mitosis has 4 phases within it: Prophase, Metaphase, Anaphase, and Telophase (PMAT)
- Produces (2) identical daughter cells - this is the process all human cells other than sex cells go through for division
Replication bubble
Active area of DNA replication
Replication fork
Point at which the DNA double helix unwinds for replication.
DNA polymerase
- Enzyme that attaches to the template DNA strand and positions complementary nucleotides during DNA replication
- synthesizes both new strands at one time (leading and lagging strand)
- DNA Polymerase only works in one direction (3 to 5 prime direction), so the lagging strand ends up being discontinuous since it’s built backwards
DNA Ligase
Enzyme that splices short segments of discontinuous lagging DNA strand together
semiconservative replication
-The process of DNA replication since each daughter double stranded DNA contains one strand from the parent DNA and one new strand
Early Prophase
- first phase of Mitosis
- Chromatin condenses forming visible chromosomes (which is in duplicated sister chromatid form)
- mitotic spindle starts to form from the centrosome
- nucleoli disappears
Late Prophase
- Nuclear envelope breaks up
- kinetochore microtobules connect to the kinetochore of the chromosome center
- nonkinetochore microtubles push against each other causing poles of cell to move farther apart
Metaphase
- the chromosomes line up in center at spindle equator/metaphase plate
- the centrosomes are at opposite ends of the cell
Anaphase
- Shortest of all phases
- centromeres of chromosomes split simultaneously becoming separate chromosomes and move away from each other
- pulled to poles by kinetochores
- nonkinetochore microtubules continue to push poles apart
Telophase
- Starts when chromosome movement stops
- each set of chromosomes (at opposite ends of cell) uncoil to resume chromatin form
- new nuclear membrane forms around chromatin
- nucleoli reappears
- mitotic spindle disappears
Cytokinesis
- Begins in late Anaphase and continues past Telophase
- actin microfilaments forms the cleavage furrow and physically pinches the cell apart
nitrogen bases of DNA
Adenine - Thymine
guanine - cytosine
Central Dogma
Process by which DNA genes are converted to a functional product (protein)
Exon
-part of the gene that codes for amino acids
introns
-non-coding segments interspersed among exons
DNA
deoxyribose nucleic acid
double helix structure that contains code for all protein structure of our cells
RNA
- ribose nucleic acid
- single stranded
- carries out the decoding and messenger functions for protein synthesis
- includes mRNA, rRNA, and tRNA
- rather than Thymine, has the baes uracil (U)
Messenger RNA (mRNA)
- RNA involved in transcription - process of copying the DNA template strand with complementary RNA bases = single mRNA strand
- Then the mRNA goes into the cytoplasm
Ribosomal RNA (rRNA)
- part of a ribosome
- consists of two subunits, which forms a ribosome where protein is synthesized
pre-mRNA
mRNA before the introns are removed
Transcription
process of encoding DNA in mRNA
Translation
process of mRNA decoding to assemble polypeptides (which involves ribosome and tRNA)
Transfer RNA (tRNA)
- carrier of amino acid and an anticodon
- the anticodon carries complementary base-pair with the codon of mRNA, adding the amino acid to growing polypeptide chain at the ribosome
codon
3-base sequence of mRNA
anticodon
on the end of tRNA contains the complementary three-base sequence to the mRNA codon
ribosome binding sites
There’s an A site, P site, and E site.
-With a tRNA in the middle P site, a tRNA comes to the A site.
-the growing polypeptide chain in the P site is transferred to the amino acid carried in the A site
-the ribosome translocates, shifting each codon position along one, so that the ‘empty’ tRNA is now in the E/exist site, and the tRNA with the polypeptide chain is in the center, P site.
The process continues until a stop codon is reached in the A site.
role of ER in protein synthesis
- a SRP (signal-recognition particle) on the ER directs the mRNA-ribosome complex where to dock
- once docked, the polypeptide chain enters the ER and sugar groups are added and overall shape changes
- protein is enclosed in a vesicle for transport to Golgi Aparatus
microRNA (miRNA)
a protective mechanism of a cell.
small RNAs that bind to and silence mRNAs made by certain exons.
Riboswitches
-Folded RNAs that act as on/off switches for protein synthesis in response to environmental conditions
Small Interfering RNAs (siRNA)
-can silence some mRNA exons from pathogenic sources
autophagy
- self eating.
- the process of disposing of nonfunctional organelles and sweeping up cytoplasm bits by forming autophages, which are then degraded by lysosomes
apoptosis
- programmed cell death
- process starts with mitochondrial membranes leaking chemicals that activate caspases enzyme
- caspases enzyme cause degradation of DNA and cytoskeleton, leading to cell death
- dead cell shrinks and is phagocytized by macrophages
hyperplasia
accelerated growth that increases cell numbers when needed
atrophy
decrease in size that results form loss of stimulation/use
Genetic Theory of Cell Aging
- end of mitosis and cell aging are programmed into genes
- Telomeres (nucleotides that protect ends of chromosomes) shorten which each cell division, so acting like an hour-glass of cell
- Telomerase is enzyme that lengthens telomeres but is absent in adult cells (only present in embryos OR cancer cells)
Progeria
disease that mimics aging caused by defective progerin protein in nuclear lamina that causes unstable, abnormal nucleus
Meiosis
- process of cell division for germ cells in humans (sperm and eggs)
- results in 4 haploid cells with only half of the DNA material as parent cell
- goes through 2 rounds of cell division
- daughter cells are not identical due to synapsis and crossing over
cell differentiation
- all cells in the body have the same genes but differentiate by active DNA (which then determines proteins) and chemical changes during embryonic stage.
- leads to different structure and function
SRP
a signal recognition particle that guides the ribosome+mRNA+amino acids to a receptor on the rough ER where the polypeptide chain enters for processing
kinesin
type of motor protein that moves the sister chromatids once they have separated in Anaphase to opposite poles of cell
nuclear lamina
rod-shaped proteins that form filaments), which maintains shape of nucleus and acts as scaffold to organize DNA
