Histology Cell Structure and Division Flashcards
What is a Cytoskeleton?
A highly dynamic (changes rapidly) system of protein filaments in the cytoplasm of a eukaryote that gives the cell a polarized shape and the capacity for directed movement
The supporting mechanism for the cell
What is diapedesis?
The crawling of cells along a surface
What are the functions of the cytoskeleton?
Responsible for:
Large-scale cellular movements such as the crawling of cells along a surface
Contraction of muscle cells
Changes in cell shape that accompany embryonic development
Provides machinery for intracellular movements
What are the 3 intracellular movements that involve the Cytoskeleton?
Transport of organelles from one place to another
Segregation of chromosomes into 2 daughter cells (mitosis)
Pinching apart of animal cells at cell division
What are the three types of protein filaments within the cytoskeleton?
Microtubules
Intermediate Filaments
Actin Filaments
What are the characteristics of Microtubules?
They are…
long stiff, cylindrical intracellular structures
20nm diameter
composed of tubulin protein
grow out of the centrosome and create a system of tracks for vesicles, organelles and other cells components to move through
Utilize motor proteins for movement of organelles
What are motor proteins?
proteins that bind to organelles within a cell and move them along microtubules (and sometimes actin filaments)
What are the characteristics of Intermediate Filaments?
Intermediate in size
10nm in diameter
Stable rope-like polymers
Made of fibrous proteins which give mechanical strength
STRONGEST OF THE 3 CYTOSKELETON PROTEINS!
Also found in the nucleus under the nuclear envelope (forming the nuclear lamina)
Which type of protein filament is rope-like and forms a nuclear lamina under the nuclear envelope of a cell - therefore strengthening the envelope?
Intermediate filaments
True or False
Protein filaments participate in cell junctions
True
What are the characteristics of Actin Filaments?
Small
7nm in diameter
made of filamentous protein
formed from a chain of globular actin molecules
Found in cross-linked bundles and networks (stronger)
Forms cell cortex
used in muscle contraction
What are integrins?
Cell surface receptors that attach cells to the extracellular matrix and mediate mechanical and chemical signals
Which protein filament type forms the cell cortex?
Actin Filaments in a network of cross-linked bundles
What are Cell Inclusions?
temporary structures in cells that can be cell products or ingested material
What are the 4 types of cell inclusions?
Glycogen
Lipids
Pigment Granules
Secretory Granules
What is glycogen?
a large branched polysaccharide found in the cytoplasm of several cell types including liver and muscle
What are lipids?
non-membrane bound droplets in the cytoplasm that vary in size
Require special stain to see with LM
What are the 2 types of lipid cell inclusions?
Neutral
Metabolic
Give an example of Neutral Lipid Cell Inclusions and where they are found in the body
Triglycerides
stored in adipose tissue
Give an example of metabolic lipid cell inclusions and where they are found in the body
Steroids as a substrate for estrogen or cortisol
What are pigment granules?
Melanin (to block UV damage)
heme (oxygen transport)
What are secretory granules?
membrane bound vesicles that contain inactive enzymes, proteins and neurotransmitters
Which organelle is the most prominent in the eukaryotic cell and contains DNA organized into chromosomes?
Nucleus
What is the nuclear envelope?
The envelope surrounding the nucleus which consists of 2 lipid bilayer membranes and is perforated by nuclear pores
the membranes are continuous with the ER (although structurally different)
What is the nuclear lamina?
a network of protein filaments that support the nuclear envelope
What do the nuclear pores on the nuclear envelope do?
Actively transport selected molecules to and from the cytoplasm
What is the Nucleolus?
the region of the nucleus where different chromosomes carrying genes for ribosomal RNA cluster (1 per nucleus)
Contains both granular and fibrous material
What is chromatin?
A complex of DNA, histones and nonhistone proteins from which chromosomes are made
Is chromatin basophilic or acidophilic? In other words how will it stain?
basophilic
What are the 2 types of chromatin?
Heterochromatin
Euchromatin
What is heterochromatin?
a highly condensed form of interphase chromatin which is transcriptionally inactive
Stains very intensely!
What is euchromatin?
the least condensed extended state of chromatin
known as active chromatin - transcriptionally active
Stains very lightly!
What are the characteristics of a Leptochromatic Nucleus?
Mostly Euchromatin
Actively Metabolically and Mitotically
What are the characteristics of a Pachychromatic Nucleus?
Mostly Heterochromatin
Not very active metabolically
What is the cell cycle?
the reproductive cycle of the cell - the orderly sequence of events by which a cell duplicates its contents and divides into two.
In order for a eukaryotic cell to divide into two, the two into four, etc. two processes must alternate…
What are these two processes?
doubling: doubling of DNA in S phase of the cell cycle
halving: of that genome during mitosis (M phase)
What are the 4 stages or broad phases of the cell cycle?
M phase
G1 Phase
S Phase
G2 Phase
What happens during M phase of mitosis?
Chromosomes are condense
Nucleus and cytoplasm divide
What is the division of the nucleus in M phase called?
mitosis
What is the division of the cytoplasm in M phase called?
cytokinesis
What happens during G1 phase of the cell cycle?
also called the gap phase, it’s the interval between completion of mitosis and the beginning of S phase
What happens during G2 phase of the cell cycle?
It’s the interval between the end of S phase and the beginning of mitosis
What are the G1, S and G2 phases (together) termed?
interphase
What is the purpose of interphase (G1, S and G2)?
to allow the cell additional time to grow and duplicate its centrosomes
What are the 6 stages of Mitosis?
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Cytokinesis
Summarize the events of Prophase
1st Stage of Mitosis
Chromosomes are condensed but not yet attached to the mitotic spindle
Summarize the events of Prometaphase
Starts with the disassembly of the nuclear envelope
Microtubules from the mitotic spindle bind to specialized protein complexes (kinetochores) and capture chromosomes
Summarize the events of Metaphase
The chromosomes align along the equatorial plate of the spindle
Summarize the events of Anaphase
connections between sister chromatids are cut by proteolytic mechanisms
Daughter chromosomes migrate to opposite poles of the spindle
Summarize the events of Telophase
Final stage of mitosis
Nuclear envelope re-assembles around each group of chromosomes to form two daughter nuclei
Nucleus expands and the condensed chromosomes decondense into their interphase state
Summarize the events of cytokinesis
Process by which the cytoplasm is cleaved in two
Begins in anaphase
involves a transient structure made of actin filaments (contractile ring)
contractile ring attaches to the membrane-associated proteins on the cytoplasmic face of the membrane
What are the main players in animal cells in relation to the cell cycle?
Early Response Transcription Factors like c-fos and c-jun
Cyclins (G1, S-phase, and M-phase cyclins) - which rise and fall with the stages of the cell cycle
CDKs (G1 CDKs, S-phase CDKs, M-phase CDKs) - levels remain fairly stable, each must bind to the appropriate cyclin in order to be activated
Cell cycle checkpoints
What can happen if cells progress to the next phase of the cell cycle before the previous phase is properly completed?
Catastrophic genetic damagge can occur
What is the purpose of a cell cycle checkpoint?
Control mechanisms at such checkpoints make sure the cell progresses through the cell cycle - completing each step in order (otherwise castastrophic genetic damage can occur)
What do mitogens do in the cell cycle?
They stimulate cells to enter G1
Summarize the initial (pre-replication) steps of the cell cycle including major players (factors, cyclins, CDKs and checkpoints)
Early response genes are induced and encode transcription factors such as c-Fos and c-Jun - which stimulate transcription of the delayed-response genes such as cyclins and CDKs.
Mitogens form - which stimulate cells to enter G1
Combination of the two above drive cell past the restriction point
Cell now committed to complete the entire mitotic division
Summarize the events of the cell cycle including the major players (cyclins, factors, etc) after the initial early-response gene induction —> restriction point
A rising level of G1 cyclins signals cell to prepare for replication
Checkpoint - if DNA damaged process will halt until repaired
Rising level of S-phase promoting factor (SPF) prepares cell to enter S phase and duplicate DNA and centrioles
S-phase cyclins degraded
M-phase promoting factor inititates assembly of mitotic spindles, breakdown of the nuclear envelope, condensation of the chromosomes (metaphase)
Checkpoint - if DNA damaged process will halt until repaired
Checkpoint - improper assembly of mitotic spindle leads to arrest in anaphase
M-phase promoting factor also activates the anaphase promoting complex (APC) which allows sister chromatids at the metaphase plate to separate and move to poles
What was the term “tumor” formerly used to denote?
any localized swelling in the body caused by inflammation or abnormal cell proliferation
Now we use it as a synonym for neoplasm
What are neoplasms?
abnormal mass of tissue formed by uncoordinated cell proliferations
Can be benign or malignant depending on their growth rate and invasiveness
