chap 3: cell cycle Flashcards
cell cycle
series of changes a cell goes through from time it is formed to time it reproduces
- interphase - cell growth and dna replication
- cell division - mitotic phase
interphase
majority of cell life spent here
nuclear material called chromatin
4 subphases:
G1: vigorous growth and metabolism
G0: gap phase in cells that permanently cease dividing, non dividing state
S: DNA replication (duplicates chromosome)
G2: preparation for division
what happens in DNA replication
occurs in INTERPHASE
Helicase untwists double helix and exposes complementary chains
Y-shaped site of replication is the replication fork
Each nucleotide strand serves as a template for building a new complementary strand
cell division
mitotic M phase of cell cycle
moves DNA from mother to 2 daughter cells
essential for body growth and tissue repair
- does not occur in most mature cells of nervous tissue, skeletal muscle, and cardiac muscle, repairs are made with scar tissue
what are the 2 events in cell division
- mitosis - 4 stages of nuclear division
- Prophase: chromosomes appear, lose nuclear envelope
- Metaphase - chromosomes line up in middle
- Anaphase - centromeres split and pulled to opposite poles
- Telophase - chromosomes change back to chromatid, nuclear envelop forms, spindles break down
PMAT - Cytokinesis - division of cytoplasm via cleavage furrow
Prophase
Early phase
chromosomes visible, each with two chromatids joined at centromere
Centrosomes separate and migrate toward opposite poles
Mitotic spindles and asters form early mitotic spindle
Late phase
Nuclear envelope fragments
Kinetochore microtubules attach to centromeres and draw them toward equator of cell
Metaphase
centromeres of chromosomes are aligned at the equator
this plane midway between poles is called metaphase plate
Anaphase
shortest phase
centromeres of chromosomes split simultaneously- each chromatid now becomes a chromosome
chromosomes (V shaped) are pulled toward poles by motor proteins of kinetochores
Telophase
begins when chromosome movement stops
2 sets of chromosomes uncoil to form chromatin
new nuclear membrane forms around each chromatin mass
nucleoli reappear
spindle disappears
Cytokinesis
begins during late anaphase
ring of actin microfilaments contracts to form a cleavage furrow - draw string
two daughter cells are pinched apart, each containing a nucleus identical to the original
control of cell division (go/stop)
Go
critical volume of cell when area of membrane is inadequate for exchange - gets too big
chemicals (growth factors, hormone, cyclin, cyclin-dependent kinases)
Stop
contact inhibition
growth inhibiting factors produced by depressor genes p53 gene which is abnormal in half of all cancers
protein synthesis
DNA is master blueprint for protein synthesis
Gene: segment of DNA with blueprint for one polypeptide
4 nucleotide bases (AGTC)
Triplets of nucleotide bases form genetic library
Each triplet specifies code for amino acid
GCA = alanine
3 types of RNA
- Messenger
- carries instructions for building a polypeptide - transfer RNA
- bring AA to ribosomes - ribosomal
- helps translate message from mRNA
transcription
occurs in NUCLEUS
- transferred info from one format to another
- transfers DNA gene base sequence to complementary base of mRNA
RNA polymerase: enzyme oversees the synthesis of mRNA
FORMATION OF MRNA IN NUCLEUS
3 steps of transcription
- Initiation: RNA polymerase binds to promoter, pries apart DNA strands and initiates mRNA synthesis
- Elongation: as RNA polymerase moves along template strand, elongating mRNA transcript one base at a time, unwinds DNA helix before it and rewinds double helix behind
- Termination: mRNA synthesis ends and completes mRNA released
translation
one language to another - language of nucleic acids to proteins
converts base set of nucleic acids to aa seq of proteins
mRNA, tRNA, rRNA
FORM PROTEIN IN RIBOSOME
genetic code
3 base seq of DNA represented by codon
- codon: complementary 3 base seq on mRNA
- certain start/stop codon production
- codon specifies diff aa
translation
mRNA attached to small ribosomal subunit that moves along mRNA to start codon
anticodon of tRNA binds to its complementary codon and adds its aa to forming protein chain
new aa added by other tRNA ad ribosome moves along rRNA until stop codon reach
