AII. Introduction to Cytology Flashcards
1
Q
is the science that deals with DNA
A
Genetics
2
Q
Each of us is composed of trillion of (?), and each of those cells contains very thin (?), a few centimeters long that play a major role in who we are, as human beings and persons. These all-important intracellular fibers are made of
A
cells
fibers
DNA
3
Q
Every time a (?) divides, its (?) is replicated and apportioned equally to two (?).
A
cell
DNA
daughter cells
4
Q
The DNA content of these cells – called the (?) – is thereby conserved.
A
genome
5
Q
This (?) is a master set of instructions, like a whole library of information, that cells use to maintain the living state.
A
genome
6
Q
Ultimately, all the activities of the cell depend on it.
A
genome
7
Q
To know the DNA is therefore to know the cell, and, in a larger sense, to know the (?) to which that cell belongs.
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organism
8
Q
− A three-base sequence in mRNA that causes the insertion of a specific amino acid into protein, or causes termination or translation
A
Codon
9
Q
Codon Example:
A
TAG-AAA-UAUGGA
10
Q
− The basic unit of heredity
A
Genes
11
Q
− Contains the information for making one RNA and, in most cases, one polypeptide
A
Genes
12
Q
− Deoxyribonucleic acid
A
DNA
13
Q
− A polymer composed of deoxyribonucleotides linked together by phosphodiester bonds
A
DNA
14
Q
− The material of which most genes are made
A
DNA
15
Q
− Ribonucleic acid
A
RNA
16
Q
− A polymer composed of ribonucleotides linked together by phosphodiester bonds
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RNA
17
Q
− The physical structure, composed largely of DNA and protein, that contains the genes of an organism
A
Chromosomes
18
Q
− One complete set of genetic information from a genetic system
A
o Genome
19
Q
− Example: the single, circular chromosome of a bacterium is its
A
genome
20
Q
Sum of all chromosomal characteristics of a cell
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Karyotype
21
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− The process of determining karyotype
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Karyotyping
22
Q
− Diagrammatic representation of karyotype
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Idiogram
23
Q
− Shows alternating dark and light band patterns
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Idiogram
24
Q
− Where genes are located
A
Chromosome
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− Contains nucleoproteins
Chromosome
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− Serves to maneuver DNA during cell division
Chromosome
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− Consists of two sister chromatids with contracted and compacted double helix of DNA
Chromosomes
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Chromosomes in human
23 pairs
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• Autosomes pairs
➢ Non-sex chromosome
➢ 1-22 pairs
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• Sex chromosomes
➢ 1 pair
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Areas of the chromosome:
Centromere
Telomere
Nucleolar organizing regions
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▪ A constriction visible on metaphase chromosomes where two sister chromatids are joined together
Centromere
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▪ Essential to the survival of the chromosome during cell division
Centromere
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▪ It is where interaction with the mitotic spindle during cell division occurs
Centromere
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– functional elements that separate the sister chromatids during cell division
− Mitotic spindle
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– attach chromosomes to the spindle fibers during cell division
− Kinetochore apparatus
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− Classification of Centromere based on its position:
❖ Metacentric
❖ Acrocentric
❖ Submetacentric
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❖ – middle
❖ – end
❖ – between middle and end
Metacentric
Acrocentric
Submetacentric
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▪ The physical end of chromosomes
Telomere
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▪ Acts as protective caps of chromosome ends
Telomere
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▪ Prevents end-to-end fusion of chromosomes
Telomere
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▪ Prevents DNA degradation resulting after chromosome breakage
Telomere
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▪ Plays a role in synapsis during meiosis
Telomere
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▪ Chromosome pairing appears to be initiated in the
subtelomeric regions
45
▪ (?) complex with telomeric DNA to protect the ends of chromosomes nucleases located within the cell
Nonhistone proteins
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The maintenance of (?) permits the binding of (?) that form the (?) at chromosome ends and regulate (?)
telomeric DNA
telomeric proteins
protective cap
telomere length
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Cells that have defective or unstable telomerase will exhibit (?) leading to chromosome instability and cell death.
shortening of chromosomes,
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(enzyme that synth esize telomeres)
telomerase
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Found in the satellite stalks of human acrocentric chromosomes
Nucleolar organizing regions
50
Where nucleoli form in the interphase of cells
Nucleolar organizing regions
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Site of rRNA genes and its production
Nucleolar organizing regions
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There are (?) NORs in human chromosomes
10
53
Two types of chromatin:
Euchromatin
Heterochromatin
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Loosely organized, extended and uncoiled
Euchromatin
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Contains active early replicating genes
Euchromatin
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Highly contracted, geneticall mitosis
Heterochromatin
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Two types of Heterochromatin:
Facultative heterochromatin
Constitutive heterochromatin
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➢ The condensed inactivated X chromosome of female cells
Facultative heterochromatin
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➢ Consists of simple repeats of nitrogenous bases
Constitutive heterochromatin
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➢ Location: around centromeres of all chromosomes; distal end of the Y chromosome
Constitutive heterochromatin
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➢ Function: Regulation of crossing over – the exchange of genes from one sister chromatid to the other during cell division
Constitutive heterochromatin
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o One X chromosome of every female cell is randomly inactivated
Facultative heterochromatin
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Condensation occurs during interphase
Facultative heterochromatin
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− An ordered set of events
Cell cycle
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− Results in cell growth and division into two daughter cells
Cell cycle
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Cell cycle
− Two alternating process:
Doubling of its genome (S phase) and halving of the genome (M phase)
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− Growth and preparation of the chromosomes for replication
G1 – “Gap 1”
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− Stage when DNA replication occurs
S – Synthesis
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− Duplication of the centrosome
S – Synthesis
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− Preparation of mitosis
G2 – “Gap 2”
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− Nuclear division
M – mitosis
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– chromosome separates
Nuclear division
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− Cytoplasmic division (cytokinesis)
M – mitosis
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− causes the cells to move from G1 to S and G2 to M
o Proteins that control the cell cycle
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− levels remain fairly stable but each must bind with the appropriate cyclin in order to be activated
CdK
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− they add phosphate groups to a variety of protein substrates that control processes in the cell cycle
CdK
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• CdK 4 –
G1 CdK
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• CdK 2 –
S phase CdK
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• CdK 1 –
M phase CdK
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− Levels rise and fall with the stages of the cell cycle
Cyclins
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• G1 cyclins
(D cyclins)
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• S phase cyclins
(cyclins E and A)
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• Mitotic cyclins
(B cyclins)
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− Also known as the cyclosome
Anaphase Promoting Complex (APC)
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− The complex is often designated as APC/C
Anaphase Promoting Complex (APC)
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Anaphase Promoting Complex (APC)
− Functions include:
• Destroys cohesin allowing sister chromatids to separate
• Degrades mitotic cyclins
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− Functions to block the cell cycle if the DNA is damaged
p53
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− It can also lead to apoptosis when the DNA damage is severe
p53
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are increased in damaged cells to allow time to repair the DNA
• p53 levels
90
is the most frequent mutation leading to cancer
p53 mutation
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extreme case of p53 mutation and leads to a high frequency of cancer in affected individuals
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− a disease that results when the regulation of the cell cycle is not controlled and normal cell growth and behavior is lost
Cancer
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− it blocks the entry into the S phase by binding to cyclins and CdK
p27
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− Reduced levels predict a poor outcome for breast cancer patients
p27
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– signals the cell to prepare the chromosomes for replication
1. G1 cyclins bind to their CdK’s
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– includes A cyclin bound to CdK2
2. S-phase promoting factor (SPF)
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➢ Enters the nucleus
2. S-phase promoting factor (SPF)
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➢ Prepares the cell to duplicate its DNA and centrosome
2. S-phase promoting factor (SPF)
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➢ As DNA replication continues, cyclin E is destroyed, and the level of mitotic cyclins begins to rise (in G2)
2. S-phase promoting factor (SPF)
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M-phase promoting factor (the complex of mitotic [B] cyclins with the M-phase CdK [CdK1]) initiates the following:
➢ Assembly of the mitotic spindle
➢ Breakdown of the nuclear envelope
➢ Cessation of all gene transcription
➢ Condensation of the chromosomes
101
▪ These events take the cell to the metaphase stage of mitosis
Condensation of the chromosomes
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▪ At this point, the M-phase promoting factor activates the
Condensation of the chromosomes
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Steps in the Cell cycle
1. G1 cyclins bind to their CdK’s
2. S-phase promoting factor (SPF)
3. M-phase promoting factor
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− allows the sister chromatids at the metaphase plate to separate and move to the poles (anaphase), thereby completing the mitosis
The Anaphase-Promoting Complex
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− Destroys B cyclins. This is also done by attaching them to ubiquitin which targets them for destruction by proteasomes
The Anaphase-Promoting Complex
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− Turns on synthesis of G1 cyclins (D) for the next turn of the cycle
The Anaphase-Promoting Complex
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− Degrades geminin, a protein that keeps the freshly-synthesized DNA in S phase from being re-replicated before mitosis
The Anaphase-Promoting Complex
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Division of chromosomes
MITOSIS
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division of the cytoplasm to form two cells (occurs at the last part of mitosis)
Cytokinesis
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− General body cells
Somatic cells
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− Same number of chromosomes as each other within the body of an organism
Somatic cells
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− Chromosomes comes in pairs
o One from the father
o One from the mother
Somatic cells
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− There are 46 chromosomes arranged in 23 pairs
Somatic cells
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Degrades geminin, a protein that keeps the freshly-synthesized DNA in S phase from being re-replicated before mitosis
o This is another mechanism by which the cell ensures that every portion of its genome is copied once – and only once – during S phase.
115
− Sex cells
o Eggs in females
o Sperm in males
Gametes
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− Have only one set of chromosomes consisting of one chromosome from each pair
Gametes
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− There are 23 individual chromosomes
Gametes
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− Cells are not dividing
Interphase
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− Chromosomes are decondensed (called chromatin) and their information is available to the cell for synthesizing products
Interphase
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− Cells spend most of their time in this intermediate non-mitotic state
Interphase
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− During interphase (in S phase), all the cells’ DNA is duplicated
Interphase
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All resulting DNA is duplicated – resulting in 4 copies of each gene instead of the normal 2 in a diploid cell
Interphase in S phase
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− Chromatin begins to coil and condense to form chromosomes
Prophase
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− Each chromosome appears to have two strands (each containing a single molecule of DNA)
Prophase
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− Each strand is called a chromatid
Prophase
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− Each chromatid is attached to its sister chromatid at the centromere
Prophase
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− At this stage, the number of chromosomes (containing a pair of chromatids) is considered to be equal to the number of centromeres
Prophase
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− The two chromatids are the result of DNA replication that takes place just before mitosis starts
Prophase
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− The nuclear envelope disappears
Prophase
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− The nucleolus disappears
Prophase
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− In cytoplasm, the spindle apparatus forms
Prophase
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− Eventually the spindle guides the separation of sister chromatids into two daughter cells
Prophase
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− Spindle grows and forms attachments to the chromosomes at the centromeres
Metaphase
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− Chromosomes move to an equatorial plate which is formed along the midline of the cell between poles
Metaphase
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− Chromosomes are at their most condensed state now
Metaphase
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− the chromosomes can be stained and will show distinctive banding patterns
Metaphase
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− Centromeres divide to create two chromosomes instead of a pair of attached chromatids
Anaphase
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− Spindle fibers shorten and the sister chromosomes are drawn to the opposite poles of the cell
Anaphase
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− Poles of the spindle apparatus are pushed apart as the cell elongates
Anaphase
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− Anaphase results in the exact division of chromosome, distributing one complete diploid complement of genetic information to each daughter cell
Anaphase
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− Nuclear envelopes reassemble and surround each set of daughter chromosomes
Telophase
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− Nucleoli reappear inside the newly formed nuclei
Telophase
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− In animal cell, a furrow appears around the cell that eventually pinches the cell into two new cells
Telophase
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− Chromosome decondense in the daughter cells to become chromatin and the cells are once again in Interphase
Telophase
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o Takes place only in the ovaries and testes
MEIOSIS
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o Involves one duplication of the DNA and two cell divisions (Meiosis I and Meiosis II)
MEIOSIS
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o Reduces the number of chromosomes from the diploid number (2n=46) to the haploid number (n=23)
MEIOSIS
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o Each gamete produced contains only one copy of each chromosome
MEIOSIS
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o Fertilization restores the diploid number in the zygote
MEIOSIS
150
o
151
a single cell divides into two
Meiosis I
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the two cells from meiosis I divides again
Meiosis II
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Prophase I important processes
Synapsis
Crossing over
154
➢ The coming together of two homologous chromosomes
Synapsis
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➢ Homologous chromosomes consist of two chromatids thus, 4 chromatids (tetrads) are actually aligned next to one another
Synapsis
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➢ Segments of DNA from one chromatid in the tetrad pass to another chromatid in the tetrad
Crossing over
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➢ Results in a genetically new chromatid
Crossing over
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➢ Important driving force in evolution
Crossing over
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➢ After this process, the four chromatid of the tetrad are genetically different from the original tetrad
Crossing over
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The Four Subdivisions of Prophase I
Leptotene
Zygotene
Pachytene
Diplotene
Diakinesis
161
− There are 46 chromosomes, each comprised of two chromatids
Leptotene
162
− The chromosomes begin to condense but are not yet visible by light microscopy
Leptotene
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− Once it takes place, the cell is committed to meiosis
Leptotene
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− follows leptotene
Zygotene
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− Chromosomes appear threadlike
Zygotene
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− Homologous chromosomes pair locus for locus
Zygotene
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o This is when synapsis occurs
− Homologous chromosomes pair locus for locus
168
o A tripartite structure
Synaptonemal complex
169
o Necessary for the phenomenon of crossing-over that will take place later in Prophase I
Synaptonemal complex
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o Synapsis of the X and Y chromosomes in males occurs only at the pseudoautosomal regions.
Synaptonemal complex
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o These regions are located at the distal short arms and are the only segments of the X and Y chromosomes containing homologous loci.
Synaptonemal complex
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o The nonhomologous portions of these chromosomes condense to form the sex vesicle
Synaptonemal complex
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− Synapsis is complete during
Pachytene
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− Chromosomes continue to condense
Pachytene
175
− Chromosomes appear as thicker threads
Pachytene
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− They now form tetrads (aka bivalents)
Pachytene
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− The phenomenon of crossing-over takes place during
pachytene
178
− Chromosomes continue to shorten and thicken
Diplotene
179
− Homologous chromosomes begin to repel each other
Diplotene
180
points at which crossing-over took place
Chiasmata
181
Chromosomes reach their greatest contraction during this last stage of prophase
Diakinesis
182
− Characterized by disappearance of the nuclear membrane and formation of the meiotic spindle
Metaphase I
183
− The tetrads line up on the equatorial plate with their centromeres randomly oriented toward opposite poles
Metaphase I
184
− The centromeres attach to spindle fibers (one centromere per spindle fiber)
Metaphase I
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− centromeres of each tetrad separate and migrate to opposite poles
Anaphase I
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− homologous chromosomes separate
Anaphase I
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o One homologous chromosome (consisting of two chromatids) moves to one side of the cell
homologous chromosomes separatehomologous chromosomes separate
188
o The other homologous chromosome (consisting of two chromatids) moves to the other side of the cell.
homologous chromosomes separate
189
homologous chromosomes separate
o Result:
23 chromosomes (each consisting of two chromatids) move to one pole and;
190
o 23 chromosomes (each consisting of two chromatids) move to the other pole.
homologous chromosomes separate
191
– the chromosome number of the cell is halved
o Reduction division
192
− In telophase, the two haploid sets of chromosomes reach opposite poles and the cytoplasm divides.
Telophase I
193
− Result: two cells containing 23 chromosomes, each composed of two chromatids.
Telophase I
194
− The nucleus reorganizes
Telophase I
195
− The chromosomes become chromatin
Telophase I
196
− A cytoplasmic division into two cells takes place
Telophase I
197
Stages of Meiosis II
▪ Interphase II
▪ Prophase II
▪ Metaphase II
▪ Anaphase II
▪ Telophase II
198
− No duplication of the DNA
Interphase II
199
− May be brief or very long, depending on the species of organism
Interphase II
200
− The chromatin material condenses, and each chromosome contains two chromatids attached by the centromere.
Prophase II
201
− The 23 chromosome pairs, a total of 46 chromatids, then move to the equatorial plate.
Prophase II
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− The 23 chromosomes pairs gather at the center of the cell prior to separation
Metaphase II
203
− The 23 chromosomes pairs gather at the center of the cell prior to separation
Metaphase II
204
− The centromeres divide, and the 23 chromosome pairs (46 chromatids) divides
Anaphase II
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− Spindle fibers move one chromosome from each pair to one pole of the cell and the other member of the pair to the other pole.
Anaphase II
206
− In all, 23 chromosomes move to each pole
Anaphase II
207
− The chromosomes gather at the poles of the cells and become indistinct
Telophase II
208
− Again, they form a mass of chromatin
Telophase II
209
− The nuclear envelope develops
Telophase II
210
− The nucleoli reappear
Telophase II
211
− The cells undergo cytokinesis as in mitosis
Telophase II
212
The 23 chromosomes in the four cells from meiosis are not identical because crossing over has taken place in [?]
Prophase I
213
The crossing over yields variation so that each of the four resulting cells from [?] differs from the other three
meiosis
214
Thus, [?] provides a mechanism for producing variations in the chromosomes
meiosis
215
Also, it accounts for the formation of four haploid cells from a single diploid cell.
meiosis
216
Comparison of Mitosis vs. Meiosis:
o Chromosome behavior
o Chromosome number
o Genetic identity of progeny
217
o Chromosome behavior
➢ Mitosis:
➢ Meiosis:
Mitosis: homologous chromosomes independent
Meiosis: Homologous chromosomes pair forming bivalents until anaphase I
218
o Chromosome number
➢ Mitosis:
➢ Meiosis:
Mitosis: identical daughter cells
Meiosis: daughter cells haploid
219
o Genetic identity of progeny
➢ Mitosis:
➢ Meiosis:
➢ Meiosis:
➢ Mitosis: identical daughter cells
➢ Meiosis: daughter cells have new assortment of parental chromosomes
➢ Meiosis: chromatids not identical, crossing over
220
– homologues don’t separate in Meiosis I
o Nondisjunction
221
➢ Results in aneuploidy
o Nondisjunction
222
➢ Can be lethal among embryos
o Nondisjunction
223
➢ Can lead to Trisomy 21, leading to Down’s syndrome
o Nondisjunction
224
➢ Sex chromosomes
o Nondisjunction
225
• Turner syndrome:
monosomy X
226
• Klinefelter syndrome:
XXY
227
– the transfer of a piece of one chromosome to another or loss of fragment of chromosome
Translocation and Deletion
228
(?) is practiced is practiced at different levels.
Genetic analysis
229
The oldest type of genetic analysis follows in Mendel’s footsteps by focusing on how traits are inherited when different strains of organisms are (?).
hybridized
230
Another type of genetic analysis follows in the footsteps of Watson and Crick and the army of people who have worked on the various genome projects by focusing on the (?) of the genetic material.
molecular makeup
231
Still another type of genetic analysis imitates Darwin and Wallace by focusing on (?) of organisms.
entire populations
