2: GENETIC BACKGROUND OF DEVELOPMENT Flashcards
a slender material inside the nucleus, usually found as colored
bodies during cell division.
Chromosome
Each chromosome is composed of ____ which separate during cell
division
sister chromatids
has a ____ or primary constriction (“waist line”), where the
kinetochore proteins are attached.
centromere
____ the sight of attachment of spindle fibers. The tip of the
chromosome arm, needed for chromosome stability, is called ____.
Kinetochore
telomeres
centromere is at the middle part of the chromosome
Metacentric
centromere is sub-median; (near the middle); long-up & short-down
Sub-metacentric
centromere is at the subterminal portion; (3/4 at tip of chromosome);
short-up & long-down
Acrocentric
centromere is at the terminal end of the chromosome
Telocentric
A sexually reproducing individuals possess ____, one
set coming from the male and another set coming from the female parent
two sets of chromosomes (2n)
complete set of chromosomes coming from either parent
Genome
Each of the chromosome in a genome has corresponding ____
identical
chromosomes or homologue.
Each ____ divides once the cell divides. This is accomplished through
cell division.
chromosome
continuity of life is based upon the reproduction of cells
cell division.
CELL DIVISION purpose
- multicellular organism to grow and
- reach the adult size,
- replaces worn-out or damaged cells, and
- keeps the total number of cells in an adult organism relatively constant.
The Key Roles of Cell Division
- unicellular organisms reproduce by cell division
- necessary for the repair and renewal of the worn-out tissues
- for the formation of new cells
- for cell growth, development and tissue differentiation
involved in in the distribution of the identical genetic materials
(DNA) to two daughter cells
Cell division
The genes are located in a
____ that is found in the nucleus
chromosome
Chromosomes are greatly involved in cell
division and in the reproductive process of an organism.
series of stages in the life of the cell is referred to as
cell cycle.
referred to as the “preparatory stage”
Interphase
▪ it is the longest phase in the cell cycle for most cells
▪ typically, it lasts for at least 90% of the total time required for the cell cycle
Interphase
a cell at interphase may appear resting under the microscope but it actually goes
through a period of ____
very high metabolic activity
- grow in size; cell increases in volume
- cell is preparing the chemicals necessary for DNA synthesis
- ER, golgi apparatus, ribosomes, mitochondria and chloroplast are
formed - chromatin, although it would appear as darkly staining materials, if
stretched would resemble a long chromatin fiber
G1 phase (first growth phase)
- each of the chromosomes is replicated by the cell
- where DNA synthesis or replication occurs
S phase (DNA synthesis)
- cell “double checks” the duplicated chromosomes for error, making any
needed repairs - active synthesis of RNA and proteins (needed for synthesis of
chromosomes) - formation of mitotic spindle occurs
- doubled chromatin fiber folds to form a chromosome
- continue until the onset of mitosis
G2 phase (second growth phase)
the period of nuclear division and cytokinesis
M-phase (Mitotic phase)
the actual division
of the cytoplasm and generation of two new daughter cells
cytokinesis
series of events wherein each cell divides to form to new daughter cells which
are exactly identical to the mother cell
Mitosis
division of the nucleus, with its contents (duplicated chromosomes: 2n), into
two identical nuclei
Mitosis
mitosis occurs in ____ except sex cells or gametes
body or somatic cell and other cells
- Chromatin in the nucleus begins to condense and becomes visible in
the light microscope and now called chromosomes - Chromosomes are thickened and become shortened
- Centrioles begin moving to the opposite ends of the cell
- Fibers extend from the centromeres. Some fibers cross the cell to form
mitotic spindle - Nucleoli and nuclear membrane completely disappear
Prophase
- The chromosomes move along the middle of the cell to ensure that the
next phase, when they separate, each nucleus will receive one copy of
each chromosome - Centrioles reached the opposite end of the nucleus
- Chromosomes become attached to the spindle fibers and move toward
the equator - Chromosomes tightly coiled and discrete; it is very much condensed
Metaphase
- At early anaphase, centromeres are duplicated and start moving apart;
sister chromatids start to separate - At late anaphase, two identical sets of chromosomes move toward the
opposite poles and spindle begins to disappear
Anaphase
- Chromatids arrive at the opposite poles of the cell
- Chromosomes in their respective poles become enclosed in a nuclear
membrane - Chromosomes begin to thin out, uncoil, and no longer visible;
- Spindle fibers disperse and cytokinesis may also begin during this
stage
Telophase
In plant tissues – the cytoplasm is divided via ____ where
separation starts from the inside of the cell towards the periphery
cell plate formation
▪ In animal tissues - cell cytokinesis occurs via ____
formation starting from the periphery
furrowing or cleavage
process by which gametes are generated for reproduction
Meiosis
meiosis occurs during ____, the whole process involved in gamete
formation
gametogenesis
the chromosome number turns to half (n)
Meiosis
reductional division; involves the separation of
homologous chromosomes resulting in two cells with haploid (n)
chromosome number
Meiosis I
equational division; the two haploid cells proceed to the
second division involving only the separation of chromatids producing
four haploid cells
Meiosis II
Chromosomes appear as long thin threads with many
bead-like structures (chromomeres) along their length.
Leptotene
Synapsis or pairing of homologous chromosomes begins.
The paired chromosomes form a bivalent consisting of
four (4) chromatids.
Zygotene
. Chromosomes are thicker due to further coiling.
- Chromatid breaks and their repair occur along the
chromosome.
- Repairing of breaks may entail exchange of segments
between sister and non-sister chromatids in a bivalent
and this is known as crossing over
Pachytene
The longitudinal separation of homologues in a bivalent
starts from the centromere and proceeds towards ends
Diplotene
Bivalents are maximally condensed and distributed
throughout the nucleus.
- Nucleolus and nuclear membrane disappeared, the
spindle has formed and Prophase I is completed
Diakinesis
- The bivalents align at the metaphase/equatorial plane.
- Centromeres attached to the spindle fibers
Metaphase I
- Univalents in each bivalent separate from each other, thus,
each anaphase group is composed of a haploid number (n)
of chromosomes
Anaphase I
- Chromosomes regroup and their coiled structures begin to
relax
Telophase I
In some species, no cytokinesis happens after Meiosis I. a
brief transitional stage called ____ occurs before the cell proceeds to the next
stage
interkinesis
meiosis II starts with ____
haploid cells
At the end of the meiosis, four new daughter cells are produced, each with a ____ number of chromosomes
diploid
– similar to mitotic prophase except that it contains haploid
chromosomes
Prophase II
- Formation of new spindle fibers; chromosomes aligned at the metaphase plate
Metaphase II
- Daughter chromosomes move toward the opposite poles
Anaphase II
- Reappearance of nucleolus and nuclear membrane; formation of four (4) haploid daughter cells
Telophase II
Cytokinesis follows (after meiosis II), forming four cells with ____ chromosome number.
haploid (n)
Meiosis may not always proceed normally. Some errors may occur affecting the
functioning of the spindle fibers of the movement of the chromosome.
The sequential events of the cell are directed by a distinct ____
Cell Cycle Control
The clock has specific checkpoints where the cell cycle stops until a go-ahead
signal is received
Two types of regulatory proteins are involved in cell cycle control:
cyclins and
cyclin-dependent kinases (Cdks)
Barresi and Gilbert
each somatic cell nucleus has the same chromosomes—and therefore the same set of genes—as all other somatic cell nuclei - known as ____
genomic
equivalence.
cell differentiation
selective production of different proteins within cells creates
cellular diversity
as the single-celled zygote divides to start the generation of all the cells making up an organism, differences in the expression of genes in these cells ____
govern maturation toward distinct cell types
many regulatory mechanisms ____ lead to this differential
gene expression
- targeting DNA access,
- RNA production and processing, and
- protein synthesis and modification
a process in which based on the unique combination of genes that are active, or “expressed”, cells become different from one another
Differential Gene Expression
a process by which cells become specialized and take on specific roles in an organism
Differential Gene Expression
By expressing different genes, cells can create different
proteins that lead to the differentiation of cell types
Three Postulates of Differential Gene Expression
- Every somatic cell nucleus of an organism contains the complete genome
established in the fertilized egg. The DNA of all differentiated cells is
identical. - The unused genes in differentiated cells are neither destroyed nor mutated;
they retain the potential for being expressed. - Only a small percentage of the genome is expressed in each cell, and a portion
of the RNA synthesized in each cell is specific for that cell type.
gene expression can be regulated at four
levels:
- Level 1: Differential gene transcription
- Level 2: Selective pre-messenger RNA processing
- Level 3: Selective messenger RNA translation
- Level 4: Differential posttranslational protein modification
regulates which proteins are allowed to remain and/or function in the cell
Level 4: Differential posttranslational protein modification
regulates which of the mRNAs in the cytoplasm are translated into proteins.
. Level 3: Selective messenger RNA translation
regulates which parts of the transcribed RNAs are able to enter the cytoplasm and become messenger RNAs.
. Level 2: Selective pre-messenger RNA processing
Level 1: Differential gene transcription
regulates which of the nuclear genes
are transcribed into pre-messenger RNA.
sequence of events that enables the use and transfer of information to make the proteins of a cell
Central Dogma
central to this theory is the ____ in double-stranded DNA, which provides the informative code or blueprints (for the precise combination of amino acids needed to build specific proteins)
order of deoxyribonucleotides
Proteins are not made directly from DNA, however; rather, the sequence of DNA bases is first copied, or transcribed, into a single-stranded polymer of similar molecules called ____, more commonly known as pre-mRNA.
heterogeneous nuclear ribonucleic acids (hnRNA)
the process of copying DNA into RNA
Transcription
RNA produced from a given gene is often referred to as a
transcript
although the transcribed pre-mRNA includes the sequences to code for a protein, it can also hold ____
non-protein-coding (simply called noncoding)
information
the pre-mRNA strand will undergo processing to excise the noncoding domains and protect the ends of the strand to yield a
messenger RNA (mRNA)
molecule
mRNA is transported out of the nucleus into the cytoplasm where it can
interact with a ribosome and present its message for the ____
synthesis of a specific
protein
▪ mRNA unveils the complementary sequence of DNA three bases at a time
▪ each triplet, or codon, calls for a ____ that will be covalently
attached to its neighboring amino acid denoted by the codon next in line
specific amino acid
leads to the synthesis of a polypeptide chain that will undergo protein folding and potential modification by the addition of various functional moieties, such as carbohydrates, phosphates, or cholesterol groups
Translation
The completed protein is now ready to carry out its specific function serving to support the ____ properties of the cell.
structural or functional
Cells that express different proteins will therefore possess different structural and functional properties, making them distinct types of cells
