Case 3 Flashcards
Explain the four distinct phases of the cell cycle
There are two broad phases- interphase and mitotic phase.
The four main phases are interphase- G1 (growth), S (growth and DNA synthesis), G2 (growth and final preparations for division), mitotic phase (mitosis).
3/4 - Interphase (has three subphases)
1. Gap 1 Subphase- cell is metabolically active, synthesizing proteins rapidly and growing vigorously.
2. S Phase- DNA is replicated, new histones are made and sorted into chromatin
3. Gap 2 Subphase- the final phase of interphase is brief- enzymes and other proteins needed for division are synthesized and moves to their proper sites.
4. Mitotic phase (I PP MAT C)
Process of nuclear division in which the chromosomes are distributed to two daughter nuclei, together with cytokinesis, it produces two identical daughter cells.
Describe the stages of mitotic cell division
In mitosis we have one cell that splits into two genetically identical daughter cells which are diploid (2n). In the body this process creates somatic cells. It occurs after Interphase (G1, S phase, G2).
Prophase I- chromatin coils and condenses
• The chromosomes start to condense (making them easier to pull apart later on).
• The mitotic spindle begins to form. The spindle is a structure made of microtubules, strong fibers that are part of the cell’s “skeleton.” Its job is to organize the chromosomes and move them around during mitosis. The spindle grows between the centrosomes as they move apart.
• The nucleolus (or nucleoli, plural), a part of the nucleus where ribosomes are made, disappears. This is a sign that the nucleus is getting ready to break down.
Prometaphase II-
• The chromosomes finish condensing, so they are very compact.
• The nuclear envelope breaks down, releasing the chromosomes.
• The mitotic spindle grows more, and some of the microtubules start to “capture” chromosomes.
Metaphase
• All the chromosomes align at the metaphase plate (not a physical structure, just a term for the plane where the chromosomes line up).
• At this stage, the two kinetochores of each chromosome should be attached to microtubules from opposite spindle poles.
Anaphase
• The protein “glue” that holds the sister chromatids together is broken down, allowing them to separate. Each is now its own chromosome. The chromosomes of each pair are pulled towards opposite ends of the cell.
• Microtubules not attached to chromosomes elongate and push apart, separating the poles and making the cell longer.
Telophase
• The mitotic spindle is broken down into its building blocks.
• Two new nuclei form, one for each set of chromosomes. Nuclear membranes and nucleoli reappear.
• The chromosomes begin to decondense and return to their “stringy” form.
Cytokenisis
The division of the cytoplasm to form two new cells, overlaps with the final stages of mitosis. It may start in either anaphase or telophase, depending on the cell, and finishes shortly after telophase.
Outline the structure of a human chromosome
2x “Chromatids” = one Chromosome
Parts include telomere, centromere that connects 2x chromatids, 2x arms (a p-arm and a q-arm)
Chromosomes have two (2) arms -p arm (petite/short arm); q arm (long arm), Chromosome always orientated with p arm at top
Centromere; Site of spindle fibre attachment (mitosis, meiosis), Necessary for proper segregation of chromosomes
Telomere; Defined ends of each Chr, responsible for stability, Contains repetitive sequence (TTAGGG)n; shorten every times a cell divides – molecular clock?
Chromatid; One copy of a duplicated chromosome, Called sister chromatids if joined by the centromere
Describe the major processes in the replication of DNA
DNA Helicase – locally unwinds the double helix (requires ATP)
DNA Gyrase – relaxes tension in DNA by introducing nicks
Single-Stranded Binding Proteins – keep the 2 DNA strands separate
RNA Primase – makes an RNA primer, starting point for replication
DNA Polymerase – adds complementary nucleotides to the growing strand, proof-reads the DNA & repairs it
Adds nucleotides to 3’ end of the growing DNA strand
Only works in the 5’-3’ direction
Newly made strand is complementary to template strand
DNA Ligase – seals up breaks in the sugar-phosphate backbone
New nucleotides added via a phosphodiester bond
A diphosphate group is cleaved from the nucleotide triphosphate
The energy release is used to drive DNA synthesis
Outline the central processes associated with cell development and the major developmental events following fertilisation up to and inclusive of the events of gastrulation
- Fertilization
Sperm’s chromosomes combine with those of an egg (secondary oocyte) to form a zygote. - Cleavage
The development of multi-cellular organisms begins from a single-celled zygote, which undergoes rapid cell division to form the blastula.
This fairly rapid phase of mitotic divisions without intervening growth- to produce small cells with high surface-to-volume ratio. After 72 hours 16 or more cells form a ‘morula’.
When do we see trophoblast?
Blastocyst Formation
Day 4 or 5 after fertilization, the embryo consists of about 100 cells, floats free in uterus, blastocyte (fluid-filled hollow sphere composed of a single layer of large, flattened cells called trophoblast cells and a small cluster of 20-30 rounded cells, called the inner cell mass clinging to the inside).
- Implantation
6-7 days after ovulation, implantation begins. It ends around the 12th day.
Embryo travels through uterine tube, floats in cavity of uterus to be implanted into uterine wall. Cleavage produces a blastocyte and the blastocyte is implanted in a uterine cell wall.
- Gastrulation
During week 3, two-layered embryonic disc transforms into a three-layered embryo. During gastrulation, the blastula folds in on itself to form three germ layers, the ectoderm (External), the mesoderm (middle), and the endoderm (inside), that will give rise to the internal structures of the organism.
Name the 3 primary germ layers and briefly outline the contributions of the primary germ layers to the 4 basic tissue types and organs of the human body
Endoderm (“Inside” bottom layer) Epithelial tissue Epithelium of digestive tract, Thyroid parathyroid, thymus glands Glandular derivatives of digestive tract
Mesoderm (“Middle” layer) Muscle and connective tissue Skeletal, smooth, and cardiac muscle Cartilage, bone, and other connective tissue Blood, bone marrow, lymphoid tissue
Ectoderm (“outside” top layer)
All nervous tissue
Epidermis of skin and epidermal derivatives
(hairs, hair follicles, sebaceous and sweat glands, nails)
Describe the major characteristics, function and locations of the four basic histological tissue types
Epithelium (from endo derm)
Simple (no layers) and stratified (multi-layered).
Extra cellular tissue- The epithelium actually have all 3 type of junctions- gap, desmosomes and tight junctions throughout the cells.
As the main functions are to cover outside and inside surfaces of body- must protect body and be selectively permeable, must also prevent leaking from the inside hence tight junctions.
Nervous (from ectoderm)
Nervous tissue can be found in the spinal cord where neurons (supported by neurological cells) travel up and down.
The function is to allow signals to travel throughout the body as such it has a body structured with two tree root like ends and a thin middle to allow it to pick up signals from axon terminals and shoot through Schwann’s cells wrapped in myelin sheath to the dendrites.
Connective (From mesoderm)
Connective tissue can be found in the bones/cartilage/blood cells/adipose/areolar cells. Connective tissue supports the body, holds it together and allows transport of molecules. Connective tissue is comprised of two elements; cells and a matrix, e.g RBC/WBC are found in blood which is fluid connective, adipocytes are found in adipose tissue/fat.
The matrix can be thought of as the substance in which the cells are embedded. The matrix can be fluid, semifluid, gelatinous, or ground substance and protein fibers. One very basic way to visualize this is to imagine Jell-O with chunks of fruit in it. Jell-O is the matrix, and the fruit represents cells.
Muscle (From mesoderm)
Smooth muscle is found in the small intestines; striated muscle can be skeletal muscle can be found in a muscle e.g biceps and cardiac muscle is found in the heart. Main function is to generate force but also to add shape/form. All muscle tissue is highly cellular and well-vascularized, containing myofilaments (networks of actin and myosin filaments)
