Chapter 4.1 : DNA Replication & The Cell Cycle Flashcards
Two type of cell division occur in human physiology :
mitosis and meiosis
Mitosis
conserves chromosome number (humans = 46)
Human ____ divide by mitosis
“somatic cells”
Another name for somatic cells
diploid cells
they have 46 chromosomes
Humans have 23 pairs of chromosomes /// total of __
chromosomes
46
– 23 came from our mother
– 23 came from our father
karyotype
an individual’s complete set of chromosomes
Typical karyotype of somatic cell has twenty-two ____
chromosomes and one pair of __ chromosomes
autosome ; sex
Meiosis
cell division that reduces chromosome number by ½
gonadal tissue
produce gametes by meiosis
Gametes are
haploid cells
these are different than our somatic cells in that they only have 23 chromosomes
An egg and a sperm combine their chromosomes to
create a new diploid cell called the ___
zygote
Genus species are defined by the
number of ______
chromosomes
The number of genes is just an index
of how many different ____ the
species is able to make.
proteins
Humans have _chromosomes.
46
A rice plant has how many chromosomes?
12
Each species of plants and
animals has a set number of
_____
chromosomes
In mitosis the cell cycle has two phases
interphase and mitotic phase.
Before a cells divides by mitosis, the cell must first
double the DNA (the genetic material) // make copy of all the chromosomes
During interphase, DNA’s chromosomes are organized as uncoiled strands called ____ // humans have __ of these strands
chromatin ; 46
Parent cell (i.e. the original cell) must double its DNA now the parent cell can give each new cell (the daughter cell) a complete copy of DNA (the chromosomes). What does this occur in and what will be the total number of chromosomes in each daughter cell?
This occurs in mitosis // 46 x 2 = 92 (or 46 identical chromosomal pairs)
Law of Complementary Base Pairing
we can predict the base sequence of one DNA strand if we
know the sequence of the other
enables a cell to reproduce one strand based on the information
in another
Law of Semi-Conservative Replication
New cell will contain DNA molecule with one side new nucleotides and the other side of the DNA molecule will have
“half” of the original DNA molecule
DNA is a ____ constructed by two strands of ____ connected by _____.
macromolecule ; nucleic acid ; hydrogen bonds
These four nucleotide molecules are used to make a strand of DNA:
Adenine, thymine, guanine, and cytosine
They are paired as:
A+T & G+C
If you have only a single
strand of nucleic acids and
an assortment of
nucleotides, then they will
hydrogen bond with their
appropriate nucleotide to
make a new strand
Steps of DNA Replication
Enzyme DNA helicase opens one short segment of helix at a time // exposing its nitrogen bases
Replication fork – the point where the DNA is opened up (like two separated halves of a
zipper)
DNA polymerase molecules move along each strand in opposite directions /// read the exposed bases /// matches complementary free nucleotides
the polymerase molecule moving toward the replication fork makes a _____
long, continuous, new strand of DNA
the polymerase molecule moving away from the replication fork makes ______
short segments of DNA at a time …DNA ligase joins them together
semiconservative replication
each daughter DNA consists of one new helix synthesized from free nucleotides and one old helix conserved from the parental DNA
new histones are synthesized in ____
cytoplasm
each DNA polymerase works at a rate of _______ per second
100 base pairs
thousands of ____ molecules work simultaneously on each ___ molecule
polymerase ; DNA
all 46 chromosomes are replicated in ___ hours
6 - 8
DNA polymerase may make mistakes and will
replace the the misplaced nucleotide. 1 in 1 billion errors happen
Mutations
changes in DNA structure due to replication errors or
environmental factors (radiation, viruses, chemicals)
Cell Cycle
a cell’s life cycle that extends through several phases to
produce two identical cells
Interphase
occurs when the cell is doing what it is programed to do.
it is during interphase that the cell also doubles its DNA
mitotic phase (M phase)
occurs when the cell
is ready to form an identical copy of
itself.
A typical human cell might take about __ hours to divide
24
What are the steps of interphase?
G1 phase, S phase, G2 phase. There is also an optional fourth
phase called G0 (G zero)
G1 phase,
First gap phase
Growth and normal
metabolic roles
S phase
S phase is when a copy of the
original DNA is made
G2 phase
Second gap phase
Growth and preparation
for mitosis
G0 (G zero) phase
Cells that leave the cell cycle
to “rest” / temporary pause
How many chromosomes are in each new daughter cell after mitotic phase?
46
Functions of mitosis
– development of the individual from one
fertilized egg to some 50 trillion cells
– growth of all tissues and organs after birth
– replacement of cells that die
– repair of damaged tissues
Four phases of mitotic phase
– Prophase
– Metaphase
– Anaphase
– Telophase
DNA is a polymer of ______ . The polymer can exist
in different forms – either as diffused _____ or condensed
_____
nucleic acids ; chromatin ; chromosomes
DNA during S phase appears as _____
chromatin
during prophase, chromatin shortens and thickens then coiling into compact rods called ______. Makes it easier to distribute
to daughter cells than when in form of _____
chromosomes ; chromatin
At end of S phase /// individual chromosomes are copied but
held together /// each pair are now called ______ _____
sister chromatids
At end of S phase, how many chromosomes are in the the parent cell?
92
Mitosis: Prophase
Chromosomes condense
and nuclear envelope
breaks down. Spindle
fibers grow from centrioles.
Centrioles migrate to
opposite poles of cell
Mitosis: Metaphase
Now chromosomes are aligned on cell equator
Cell equator
swaying slightly and awaiting signal that
stimulates each of them to split
Mitotic spindle
lemon-shaped array of spindle
fibers
– long spindle fibers (microtubules) attach to
chromosomes at kinetochore
– shorter microtubules (aster fibers) anchor
centrioles to plasma membrane at each end
of cell
Kinetochore
point where chromatids attach to each
other
Mitosis: Anaphase
separates the two chromatids at centromere
(point of chromatid attachment)
During anaphase, ________ in kinetochore crawl along the spindle fiber as the fiber itself is ______ and disassembled at the chromosomal end
motor proteins ; ‘chewed up’
Each daughter cell following mitosis are genetically ____
identical
Mitosis: Telophase
chromatids (the daughter chromosome) cluster on
each side of the cell
During telephase, rough ER produces new _____ around each cluster and each nucleus forms ____
nuclear envelope ; nucleoli
Cytokinesis
the division of cytoplasm into two cells
cell eventually pinches in two
telophase is the end of mitosis but overlaps with
cytokinesis
Cytokinesis creates the ______ around the equator of cell
cleavage furrow
When may cells divide by mitosis?
- If they have enough cytoplasm for two daughter cells
- If they have doubled their DNA (made complete copy of all chromosomes).
- If they have adequate supply of nutrients
- If they are stimulated by growth factor – chemical signals secreted by blood platelets, kidney cells, and other sources
- If neighboring cells die. This opens up space in the tissue for new cells and prevents contact inhibition.
What will inhibit mitosis?
- When nutrients or growth factors are withdrawn
- If existing cells are too closely packed with neighboring cells / no room for new cells
- Contact inhibition
Contact inhibition
the cessation of cell division in response to contact with other cells
father of Classical Genetics.
Gregor Mendel
coined the terms dominant and recessive traits
Charles Darwin wrote ________. He explained how
_____ and _______ create new species.
On the Origin of Species ; Evolution ; Natural Selection
Darwin and Mendel work is known as _______
Classical Genetics
Our understanding of genetics was updated and renamed ____ in the 1940’s to incorporate the role of DNA .
Modern Genetics
epigenetic trait
stably heritable phenotype resulting from changes in a chromosome without alterations in the DNA sequence
