Embryological Development Flashcards
Why is the study of human embryology and growth and development important to dentistry?
- Providing care requires an understanding of how the craniofacial complex originates, develops and matures.
- Helps you understand current and developmental research
- Not a static subject; understanding improves with study
- Helps you to identify normal and abnormal development
- Sheds light on birth defects and syndromes so you can better clinically manage those patients
In the nucleus of each cell, the DNA is packaged into thread-like structures called:
Chromosomes
What are chromosomes made of?
DNA tightly coiled many times around proteins called histones that support its structure
Are chromosomes visible? (Even under a light microscope)
No, only visible when the cell is dividing.
What is a centromere?
a constriction point which divides the chromosome into two sections, or “arms.”
What are the two “arms” of a centromere?
Short arm: P
Long arm: Q
How many chromosomes are contained by the nuclei of most human cells?
46
What is meant by homologous chromosomes (or homologs)?
The 46 chromosomes are divided into 23 paris; each of these pairs are alike, but not necessarily identical
How many pairs of autosomes?
22
How many pairs of sex chromosomes?
1
Which pair of sex chromosomes result in females?
XX
Which pair of sex chromosomes result in males?
XY
What is diploid?
When a cells chromosomal number consists of two sets of chromosomes, one set from the mother, and one set from the father. (Denoted as 2N)
What must happen before a cell can divide?
Replicate DNA
What are sister chromatids?
The two identical chromosomes resulting from DNA replication
What is an allele?
a variant form of a gene
When do chromosomes appear as a thick, x-shaped structure?
After undergoing additional compaction at the beginning of mitosis. Fully condensed and replicated.
What is chromatin?
The combination of DNA, histone, and other proteins that make up chromosomes
Where is chromatin found?
inside the nuclear envelope of eukaryotic cells
What are the extended and condensed forms of chromatin?
euchromatin (extended form) heterochromatin (condensed form)
What is the structure of the first level of packaging during mitosis?
Euchromatin, or “Beads-on-a-string”
What does condensed chromatin (heterochromatin) allow for?
The cell’s DNA to be packed into the nucleus. Think telephone chord.
What is the centrosome?
An organelle located near the nucleus in the cytoplasm that divides and migrates to opposite poles of the cell during mitosis.
The centrosome consists of two:
Centrioles, oriented at right angles to each other and are embedded in a mass of amorphous material containing more than 100 different proteins
Where do the centrosomes move just before mitosis?
Apart, until they are on opposite sides of the nucleus.
What are mitotic spindle fibers?
Clusters of microtubules that grow out from each centrosome with their plus ends growing toward the metaphase plate during mitosis.
What are the three distinct types of microtubule fibers in the mitotic spindle?
kinetochore microtubules
polar microtubules
aster microtubules
What is the purpose of the 3 types microtubule fibers?
All three emanate from the centrosomes and serve to pull and push the sister chromatids apart toward the opposite spindle poles.
What are kinetochores?
proteins associated with the centromere of chromatids
How many kinetochores are there per replicated chromosome?
2, one for each sister chromatid on opposite sides of the chromosome
Where do the kinetochore microtubules attach?
A kinetochore microtubule from one pole attaches to one kinetochore, while a kinetochore microtubule from the opposite side attaches to the other kinetochore
During which phase of mitosis does the kinetochore microtubule grow from the centrosome?
Prophase
During which phase of mitosis does the kinetochore microtubule bind with the proteins within the kinetochore?
Prometaphase
What happens when the kinetochore microtubule binds with the kinetochore?
The effect of being grabbed by kinetochore microtubules from opposite poles is a balancing of opposing forces, which results in alignment of the chromosomes at the spindle equator during metaphase
In mammalian cells, many kinetochore microtubules are associated with what?
Each sister chromatid
What are polar microtubules?
The microtubules from opposite poles that do not attach to the kinetochores but do overlap at the midpoint between the two poles
What are aster microtubules?
They point away from the spindle equator and are attached to the cell’s cortex
All three of the spindle microtubules grow out from where?
The centrosome
All three of the spindle microtubules are polymers composed of:
alpha and beta tubulin subunits
How does a microtubule grow?
By the addition of tubulin subunits to one end of the polymer (plus end)
(T/F) A microtubule has a distinct polarity
True
What is the plus end of a microtubule?
The growing end
What is the minus end of a microtubule associated with?
Centrosome
How does the plus end of a microtubule grow or shrink?
By addition (polymerization) or loss (depolymerization) of tubulin subunits
What are motor proteins?
Proteins that can travel along the length of a microtubule in an energy-dependent fashion.
Motor proteins utilize the energy of what to move along microtubules?
adenosine triphosphate (ATP) hydrolysis
Motor proteins are required for what?
- Spindle formation
- Chromosome alignment and segregation
- The cell to avoid aneuploidy
What is aneuploidy?
The presence of an abnormal number of chromosomes in a cell, a hallmark of cancer.
What is the most basic function of the cell cycle?
Duplicate accurately the DNA in the chromosomes and then segregate the copies into two genetically identical daughter cells.
What is the S phase of the cell cycle?
DNA duplication
What percentage of the cell-cycle time does the S phase take in a typical mammalian cell?
Half, 10-12 hours.
What is the M phase of the cell cycle?
chromosome segregation and cell division
What are the four sequential phases the eucaryotic cell cycle is traditionally divided into?
G1, S, G2, and M
Which phases make up interphase?
G1, S, and G2
What is the purpose of gap phases?
To allow more time for growth
What happens to the nuclear envelope at the end of prophase?
Disappears, signaling the beginning of prometaphase
Where does the mitotic spindle form?
Mitotic spindles form from each pair of centrioles as they migrate in the cytoplasm towards different poles of the cell.
What is the mitotic spindle made of?
microtubules and other proteins
In Mitosis, what marks the beginning of prophase?
chromosomes thicken and coil, and the nucleolus shrinks and disappears.
In mitosis, where are the centrosomes during metaphase?
At opposite poles of the cell
In Mitosis, how many individual chromatids are there during metaphase?
92 (46 pairs)
(T/F) Chromosomes are at their least coiled and condensed during metaphase.
False, they are at their MOST coiled and condensed.
During mitosis, where are the chromosomes arranged during metaphase?
The metaphase plate: a plane equidistant from from the two poles
In mitosis, when does anaphase begin?
when the duplicated centromeres of each pair of sister chromatids separate, and the now-daughter chromosomes begin moving toward opposite poles of the cell due to the action of the spindle.
In mitosis, what happens by the end of anaphase?
a complete set of chromosomes has assembled at each pole of the cell.
In mitosis, where are the chromosomes during telophase?
-The chromosomes assemble in sets at the two poles and begin to uncoil
In mitosis, during which phase does the nuclear envelope reform around each chromosome set?
Telophase
(T/F) Nuclear division by mitosis is complete by the telophase.
True
What is Cytokinesis, and when does it generally happen?
Division of the cytoplasm, usually in progress before the nuclear division is complete.
What is a cleavage furrow?
In animal cells, cytokinesis involves the formation of a cleavage furrow resulting in the pinching of the cell into two.
What are the 4 bases of DNA?
Adenine, Thymine, Cytosine, Guanine
Which of the DNA bases pair with each other?
A pairs with T
C pairs with G
How many chains of nucleoides are there in DNA?
2… Double Helix
(T/F) RNA is typically single stranded
True
What processes are RNA needed for?
protein synthesis and DNA replication
What are the 4 bases of RNA?
Adenine, Guanine, Cytosine, Uracil
Which of the RNA bases pair with each other?
A pairs with U
G pairs with C
What is the result of an error in mitosis?
Incorrect DNA cpoy
What are the two types of errors (mutations) in improperly copied DNA?
Silent mutations, which have no impact on the DNA sequence
Missense mutations, which change a DNA sequence and often impact the associated function.
When does cancer occur?
when the normal “checkpoints” regulating mitosis are ignored or over-ridden by a cancer cell, resulting in uncontrolled cell division.
Benign tumors (are/ are not) cancerous
Are not
Malignant tumors (are/ are not) cancerous.
Are
What is metastasis?
Metastasis is the spread of cancer cells to new areas of the body (often by way of the lymph system or bloodstream).
What is metastatic cancer?
one which has spread from the primary site of origin into different area(s) of the body.
What are secondary tumors?
Tumors formed from cells that have spread
What is the difference between regional and distant metastasis?
Cancer spreads to areas near the primary site (regional metastasis), or to parts of the body that are farther away (distant metastasis).
What type of treatment does metastatic cancer generally require?
Systemic therapy, by medications given by mouth or injected into the bloodstream to reach cancer cells throughout the body, such as chemotherapy or hormone therapy.
What do gene mutations do?
Tell a cell to grow and divide more rapidly or nor preform apoptosis when is should (live longer than programmed).
(T/F) Gene Mutations occur infrequently during normal cell growth.
False. However, tumor suppressor genes normally discover the mistake and correct the problem.
What are tumor suppressor genes?
A mechanism in cells that recognizes when a mistake occurs and repairs it.
How do cancer cells relate to tumor suppressor genes?
Cancer cells lose the controls (tumor suppressor genes) that tell them when to stop growing.
What are the two causes of gene mutations?
Hereditary (Small percentage) & Environment (Radiation, viruses, carcinogens, obesity, hormones, chronic inflammation, lack of exercise)
What are some factors that increase the risk of cancer?
Age, habits, family history, health conditions, enviornment
What are some signs of oral cancer?
Sore that doesn’t heal, discoloration, lump in your cheek, persistent sore throat, voice changes, numbness, weight loss, jaw swelling, constant feeling that something is caught in your throat
What are some tests to determine the presence of cancer?
Biopsy, MRI, CT scan, X-ray, PET scan
T
- Carcinoma in situ.
- An early stage cancer, meaning that the disease is still localized, or contained within the top layers of cells lining the oral cavity and oropharynx.
- Cancer cells have not invaded the deeper layers of oral or oropharyngeal tissue.
T2
tumor is larger than 2 cm across, but smaller than 4 cm.
T3
tumor is larger than 4 cm across.
T1
tumor is 2 cm across or smaller.
T4a
-the tumor is growing into nearby structures. –At this stage, the oral cancer is called a moderately advanced local disease.
The areas to which cells have spread vary according to the type of oral cancer.
T4b
- the tumor has grown through nearby structures and into deeper areas or tissues.
- At this stage, the cancer is called very advanced local disease.
N1
- The cancer has spread to one lymph node on the same side of the head or neck as the primary tumor.
- This lymph node is smaller than 3 cm across.
N2a
The oral cancer has spread to one lymph node on the same side as the primary tumor, and the lymph node measures 3–6 cm across.
N2b
The oral cancer has spread to 2 or more lymph nodes on the same side as the primary tumor. No lymph nodes are larger than 6 cm across.
N2c
The oral cancer has spread to one or more lymph nodes on both sides of the neck or on the side opposite the primary tumor. No lymph nodes are larger than 6 cm across.
N3
The cancer has spread to a lymph node that measures more than 6 cm across.
M0
No Metastatis
M1
The oral cancer has spread to distant sites outside the head and neck region (for example, the lungs, liver or bones).
What is Meiosis?
a sequence of two specialized cell divisions (Meiosis I and Meiosis II) by which the number of chromosomes in the gametes is halved.
How many mature gametes are produced during meiosis?
4, containing 23 chromosomes
What happens to the centrioles and chromosomes leading up to meiosis?
They are replicated
What are the phases of meiosis?
prophase, metaphase, anaphase and telophase…the cell goes through this cycle twice (meiosis I and meiosis II)
What makes meiosis I unique?
genetic diversity is generated through crossing over and random positioning of homologous chromosomes.
What happens during synapsis?
crossovers (cross-connections that form from breakage and rejoining between sister chromatids) can occur between the paired bivalents, leading to genetic recombination between the strands involved.
What is chiasma?
The point at which paired chromosomes remain in contact, and exchange of genetic material occur between the strands
On average, how many crossovers events occur on each pair of human chromosomes during meiosis I?
Between 2 and 3
What is the chromosomal number in meiosis I?
Starts as Diploid 2n and is reduced to Haploid 1n
In meiosis, each centrosomes kinetochore fibers attach to what?
One kinetochore microtubule attaches to one of the chromosomes of the homologous pair at the centromere, separating the homologous pair, but not sister chromatids. In mitosis, the kinetochore microtubules from each centrosome attache to different kinetochores of the same chromosome, effectively separating the sister chromatids.
In meiosis I, the position of each chromosome in the bivalents is:
Random
In meiosis, during metaphase 1, where do each pair of bivalents align?
On the metaphase plate.
In meiosis, during anaphase 1, what happens to homologous chromosomes?
They seperate
In meiosis, what happens in telophase 1?
One double-stranded chromosome of each homologous pair is distributed to each daughter cell
Meiosis I proceeds directly to Meiosis II without doing what?
Going through interphase
Which does meiosis II resemble more, mitosis, or meiosis I?
Mitosis
(T/F) During prophase II, DNA replication takes place
False
What happens to spindle fibers in prophase II?
Reform and attach to centromeres
How many haploid nuclei are formed in telephase II?
4
Are the 4 haploid cells formed in telephase II identical?
They are not identical, as random arrangements of bivalents and crossing over in meiosis I leads to different genetic composition of these cells.
What is ploidy?
refers to the number of full, single set(s) of chromosomes in a cells nucleus, not including duplicated DNA set(s) in the nucleus.
What does “n” refer to?
the ploidy of a cell.
What is the N number?
refers to the number of full, single set(s) of chromosomes including duplicated DNA sets in the nucleus.
Do the ploidy and the N number always coincide?
No, each chromosome contains one or two molecules of DNA at different stages of the cell cycle (whether mitotic or meiotic)
What are primordial germ cells (PGC’s)?
Cells that give rise to gametes in both males and females. Their lineage constitutes the germ line.
Between four and six weeks, the PGC’s migrate where?
From the yolk sac to the wall of the gut tube, and from the gut tube via the mesentery of the gut to the dorsal body wall.
What happens if a PGC becomes stranded during migration?
It may come to rest at extragonadal sites, which may give rise to a type of tumor called a teratoma.
Where do PGC’s come to rest?
In the dorsal body wall, these cells come to rest on either side of the midline in the loose mesenchymal tissue just deep to the membranous lining of the coelomic cavity at the level that will form the gonads.
What are immature gametes called?
Spermatogonia (males)
Oogonia (females)
What is gametogenesis
development and production of the male and female mature gametes.
What is permatogenisis?
In males, the production of the mature gamete called spermatozoa
What is oogenesis?
In females, the production of the mature gamete called an secondary oocyte
What happens to the the spermatogonia and oogonia during gametogenesis?
They undergo meiosis where they are changed from diploid 2N to haploid 1N.
Why does the number of spermatogonia not decrease?
They are constantly undergoing regular mitosis
What is the term for PGCs in the testes?
spermatogonia
How many meiotic divisions do the spermatogonia undergo?
Two, which gives rise to four future-spermatozoa, with each containing half of the normal human genetic content (haploid 1N)
The spermatogonia pass through the ___________, supported by ____________
seminiferous epithelium, Sertoli cells
In females, meiosis of primordial germ cells is completed (before/ after) birth
After. The primordial germ cells develop in the fetus, and before birth, meiosis begins. Then meiosis freezes right at the start of the first meiotic prophase division and resumes when hormone levels are right in the female.
What is an oogonia?
one of the undifferentiated Primordial germ cells giving rise to oocytes
How many oocytes are in the ovary
Millions
Oognias are stopped in which phase of meiosis I?
Prophase I
When does a single oocyte resume meiosis?
Only when signaled by hormones
(T/F) Oocytes undergo cytokinesis the same as any other cell
False
What is symmetrical cytokinesis?
During mitosis and spermatogenesis, cytokinesis of the two daughter cells occurs right down the middle of the parent cell
Is cytokinesis symmetrical or asymmetrical during oogenesis?
Asymmetrical
What is formed during asymmetrical cytokinesis?
a secondary oocyte cell and a polar body cell are formed
How big is a secondary oocyte?
Very large cell with a very small polar body.
What is the zygotes plasma membrane surrounded by?
a glycoprotein layer called The zona pellucida
After ovulation, each oocyte only completes Meiosis II if?
Fertilization occurs
What happens when the primary oocyte completes meiosis I?
The follicle matures during ovulation, resulting in a secondary oocyte and the first polar body.
What happens to the zygote within 24 hours of fusion?
It undergoes a series of mitotic cell divisions called Cleavage as it travels down the oviduct
What is the embryo called by the 32-cell stage and how does it look?
The embryo has the appearance of a small mulberry and is called a Morula
(T/F) After fusion, cell divisions are accompanied by cell growth
False, cell divisions are not accompanied by cell growth but sub divide the large zygote into many smaller daughter cells
What are blastomeres?
smaller daughter cells subdivided from the large zygote
What is trisomy 21?
One cell has two 21st chromosomes instead of one, so the resulting fertilized egg has three 21st chromosomes- Down Syndrome
What is nondisjunction?
Two copies of chromosome 21 failing to separate during the first or second meiotic division
Nondisjunction can happen during gametogenisis in either parent, but is most commonly seen in males or females
Females. Chances increase with age
What is Robertsonian Translocation?
Sometimes, a copy of chromosome 21 in a developing gamete becomes attached to the end of another chromosome, such as chromosome 14, during the first or second division of meiosis. May also cause Down Syndrome
What percent of cases of trisomy 21 are due to Robertsonian Translocation?
3 to 4%
What is partial trisomy 21?
A child may only have triplication of part of the 21st chromosome instead of the whole chromosome
What percentage of adults with Down Syndrome have an incidence of periodontal disease?
90-96%
What is Klinefelter syndrome?
Males that have an extra X chromosome in most of their cells. (XXY)
What are clinical challenges associated with Klinefelter syndrome?
Possible crowding, growth abnormalities, taurodaontism
What is turner syndrome?
When one normal X chromosome is present in a female’s cells and the other sex chromosome is missing or structurally altered.
What are some clinical presentations of Turner syndrome?
Extra folds of skin on the neck, low hairline, early loss of ovarian function, heart defects,
T, N and M stands for what in TNM staging?
Tumor Size
Node
Metastesis
T/F An oocyte is the same thing as a primordial germ cell?
F
T/F A spermatogonia may be called a primordial germ cell?
T
What is the SHOX gene?
The gene involved with the short stature (maturation problems of bones in the arms and legs) of people suffering from Turner Syndrome
