Lesson 4 Flashcards
nucleus
usually the largest organelle in the cell, contains genetic material
nuclear envelop
double membrane around the nucleus
perforated by nuclear pores
nuclear pores
formed by a ring of proteins called the nuclear pore complex, perforates the nuclear envelope
what do nuclear pores do for the nuclear envelope? (2)
regulates molecular traffic
holds the two membrane layers together
what supports the nuclear envelope?
a web of protein filaments called the nuclear lamina
nucleoplasm
the material within the nucleus
what comprises nucleoplams?
chromatin (DNA and proteins) and one or more nucleoli where ribosomes are produces
nuceleolus
area in the nucleus that is composed of RNA, enzymes and histones
abundant in cells that produce lots of proteins
what types of cells produce lots of proteins? (3)
ex. liver, nerve, and muscle cells
what does the nucleolus produce?
rRNA and ribosomal subunits essential for translation
ribosomes
composed of rRNA and ribosomal proteins, form subunits that are used in translation
what organelle shares it’s membrane with the nucleous?
the ER
deoxyribonucleic acid (DNA)
long, thread-like molecule with uniform diameter, varied in length
how many chromosomes are in the nucleus of most human cells?
46
DNA is comprised of polymers called…
nucleotides
three components of a nucleotide
- a sugar (deoxyribose or ribose)
- a phosphate group
- a nitrogenous base
purines
adenine and guanine
double-ringed structure
pyrimidines
cytosine, thymine, and uracil
single-ringed structure
bases are held together by what type of bonds?
hydrogen bonds
how many bonds does A-T make?
two
how many bonds does G-C make?
three
main function of DNA
carry instructions (genes) for the synthesis of proteins
gene
an information-containing
segment of DNA that codes for the production of a
molecule of RNA that most often plays a role in
synthesizing one or more proteins
functional unit of heredity
what roles do non-coding DNA play? (2)
- add to chromosome structure
- regulates gene activity
chromatin
fine, filamentous DNA material complexed with proteins called histones
histones
proteins around which DNA winds
cluster in groups of eight molecules
nucleosome
DNA wrapped around histones
sister chromatids
two parallel filaments of identical DNA
chromatids are joined at the _______
centromere
kinetochores
protein plaques on each side of the centromere, play a role in cell divison
DNA to mRNA is called….
transcription
where does transcription occur?
in the nucleus
mRNA to protein is called…
translation
where does translation occur?
the cytoplasm
what enzyme is used during transcription?
RNA polymerase
what does RNA polymerase do in transcripton?
- binds to the start sequence in DNA, opens the helix
- reades bases from one DNA strand to build a complementary strand of mRNA
- rewinds the DNA helix behind it allowing a gene to be transcribed by several polymerase molecules
pre-mRNA
“immature” RNA produced by transcription, needs to undergo splicing
enzymes within the nucleus remove _____ and splice together _____
introns
exons
translation
nucleotide language converted into amino acid language
messenger RNA
carries code from nucleus to cytoplasm
has protein cap that is a recognition site for the ribosome
transfer RNA
delivers a single amino acid to the ribosome
contains and anticodon
ribosomes have three sites
E site, P site, and A site
translation: initiation (3)
- ribosomes assemble with mRNA in the cytosol
- small subunit binds to the leader sequence of mRNA, and the large subunit joins
- when AUG is reached, protein synthesis begins and tRNA brings the first amino acid, methionine
translation: elongation (4)
- the next tRNA brings a new amino acid and binds to the A site
- the ribosomes creates a peptide bond between the first and second amino acids
- the ribosome moves down the mRNA by one codon, the growing peptide is now attached to the tRNA in the P site
- process continues
translation: termination (3)
- ribosome reaches a stop codon
- A site binds a protein called a release factor
- ribosome disassembles and dissociates from mRNA
polyribosomes
ribosome clusters translating the same mRNA molecule simultaneously
protein processing and secretion (6)
- protein formed by ribosomes on rough ER
- protein packages into transport vesicle which buds from the ER
- transport vesicles fuse into cluster to form a new cis cistern of the Golgi
- Golgi complex modifies the proteins
- trans cistern breaks up into cargo-laden golgi vesicles
- secretory vesicles release protein by exocytosis
gene regulation example: casein
- hormone prolactin binds to receptors of mammary cells
- receptors trigger activation of a regulatory protein in the cytoplasm
- regulatory protein moves into the nucleus and binds to the DNA near the casein gene
- the binding enables RNA polymerase to bind to the gene and transcribe it, producing the casein mRNA
- the casein mRNA moves to the cytoplasm, binds to ribosomes, and starts translation
- the golgi complex packages casein into secretory vesicles
- the secretory vesicles release the casein by exocytosis, and it becomes part of the milk
four steps of DNA replication
- unwinding the helix from histones
- unzipping small portions of the helix by DNA helicase, forming the replication fork
- DNA polymerase moves along each strand, synthesizing complementary strands
- segments are connected by DNA ligase
- new histones are synthesized, used to organize new DNA strands into nucleosomes
interphase - G1 - characteristics
- interval between cell division and DNA replication
- cell carries out normal tasks and synthesizes proteins and materials needed for the next phase
interphase - synthesis - characteristics
cell replicated all nuclear DNA and duplicated centrioles
interphase - G2 - characteristics
cell repairs DNA replication errors, grow, and synthesizes enzymes that control cell division
G zero phase
cells that have left the cycle and cease dividing for a long time or permanently
ex. skeletal muscle cells, cardiac muscle cells, neurons
prophase characteristics
- genetic material condenses into compact chromosomes
- nuclear envelope disintegrates
- centrioles sprout spindle fibers
metaphase characteristics
- chromosomes aline on cell equator
- spindle fibres form the mitotic spindle
- centrioles complete a starlike aster which anchors itself into the cell membrane
anaphase chracteristics
- enzyme cleaves sister chromatids at centromere
- single daughter chromosomes migrate to opposite sides of the cell
telophase characteristics
- chromosomes cluster
- rough ER makes new nuclear envelope
- chromosome uncoil
- mitotic spindle disintegrates
- each nucleus forms nucleoli
cytokinesis characteristics
- division of cytoplasm
- starts in late anaphase
- achieved by myosin proteins pulling on actin in the terminal web
when do cells divide? (5)
- have enough cytoplasm for two cells
- have replicated their DNA
- have adequate supply of nutrients
- stimulated by growth factor, increase in MPF (M-phase promoting factor)
- neighboring cells die
when do cells stop dividing? (3)
- snugly contact neighboring cells
- nutrients or growth factors are withdrawn
- experience contact inhibition
- stopping of cell division in response to contact with other cells
cachexia
severe wasting away of depleted tissues