LESSON 7 CHROMOSOMES Flashcards
Chromosomes were first described by [?] in 1879-1892 as accurate counting of chromosomes, first observed chromosomes in cell division.
Walther Flemming, Eduard Strasburger and Eduard van Beneden
The term “Chromosome”, however was first used by [?] in 1888.
Henrich Wilhelm Gottfried Waldeyer
They were given the name chromosome (Chroma = colour; Soma = body) due to their marked affinity for [?].
basic dyes
: end color of chromosome using Giemsa
Purple/blue
Chromosomes are composed of thin chromatin (made up of DNA coiled in histones) threads called
Chromatin fibers.
• These fibers undergo folding, coiling and supercoiling during (?) so that the chromosomes become progressively thicker and smaller.
prophase
: starts to coil to become a chromosome for easier distribution to daughter cells upon mitosis
Prophase
nuclear membrane disappears (also in metaphase and anaphase)
Prophase
DNA is coiled to a dense chromosome to make sure that the daughter cells receive all 46 chromosomes
Prophase
Therefore, chromosomes become readily observable under light microscope.
Metaphase:
: distribution of chromosomes
Metaphase
At the end of cell division, on the other hand, the fibers uncoil and extend as fine chromatin threads, which are not visible at light microscope
Telophase and Cytokinase
longer part of the chromosome is not visible and goes back to chromatin
Telophase and Cytokinase
nuclear membrane returns
Telophase and Cytokinase
discovered the chromosomal theory of inheritance in 1902
Walter Sutton and Theodor Boveri
It is shown that chromosomes occur in pairs, one parent contributes each member of the pair, and the pairs separate during meiosis.
chromosomal theory of inheritance
The parent gives [?] or pieces of chromosome each
23:23
: a cell division that happens among sex cells (sperm and ova) only
Meiosis
suggested that genes reside in chromosome as seen in Drosophila.
• Thomas Hunt Morgan
became their muse for understanding genes and inheritance.
Fruit flies
The genomes of [?] are contained in single chromosomes,
prokaryotes
prokaryotes are complexed with histone-like proteins in a structure termed the
nucleoid
• “naked” DNA
PROKARYOTIC
• Attached to plasma membrane
PROKARYOTIC
Do not have a true nucleus, not enclosed by a nuclear membrane
PROKARYOTIC
Does not have a nuclear membrane anymore because they are coiled and in a condensed form, unlike in humans which is not condensed during interphase information
PROKARYOTIC
Chromosome and plasmids caries the genetic info
PROKARYOTIC
• Prokaryotes also frequently carry one or more smaller independent circular DNAs, called
plasmids
• Bacterial cells may also contain [?] that are autonomously self replicating extrachromosomal DNA that confer special characteristics to the cell in which it is present.
plasmids
They replicate at their own phase w/o DNA involvement
plasmids
• Unlike the larger chromosomal DNA, [?] typically are not essential for bacterial growth
plasmids
carry genes that confer desirable traits to the bacteria, such as antibiotic resistance
plasmids
Passing antibiotic resistant gene will produce “superbugs”
plasmids
Also distinct from chromosomal DNA, plasmids can be present in many complete copies per cell.
• Eg.
Antiobiotic Resistance genes
Plasmids include the fertility factor (F+ plasmid)
Ex.
Multidrug resistant TB
- Plasmid is passed thru a
pilus
- Chromosomal DNA is passed thru
binary fission
- Conjugation
PLASMID DNA
- Antibiotic resistance is passed thru
PLASMID DNA
- Cell division
CHROMOSOMAL DNA
- Found in bacteria
Plasmids
- no need for nuclear membrane de to organized chromosomal DNA
Plasmids
prokaryotes compress their DNA into smaller spaces is through
Supercoiling
could be a means of identification of bacteria
Supercoiling
The helix twists on itself; twists to the right
Positive supercoil
Helix twists on itself in the opposite direction; twists the left
Negative supercoil
Most common type of supercoiling
Negative supercoil
The Bacterial Chromosome Is Condensed Into
Chromosomal Domains
• The circular DNA is packaged into a region of the cell called the [?] where it is organized into 50 or so loops or domains that are bound to a central protein scaffold, attached to the cell membrane.
nucleoid
Single, circular DNA molecule located in the nucleoid region of cell
Bacterial Chromosome
Is an enzyme necessary for the unwinding the coils to the right. In order for DNA to control the synthesis of proteins, and in order for DNA to reproduce.
DNA gyrase (Topoisomerase II)
They cut the DNA, and at the end of the process connect it again
DNA gyrase (Topoisomerase II)
: twists itself to look like a flower
Histone-like
possess multiple large linear chromosomes contained in the cell’s nucleus.
Eukaryotes
DNA Is Organized into [?] in Eukaryotes.
Chromatin
The complexes between eukaryotic DNA and proteins (histone and non-histone proteins) are called [?]
Chromatin
typically contains about twice as much protein as DNA.
Chromatin
Complex interactions between [?] in the chromosomes regulate gene and chromosomal function
proteins and nucleic acids
[?] is (-) charged; [?] is (+) charged = affinity to each other
DNA
Histone
Left sister chromatid has the same genetic info with the right sister chromatid to divide into two and pass to each daughter cell
Chromosome Structure
: DNA form. To easily pass it to the daughter cells, it will be condensed to become a chromatin.
Interphase
: chromosome
Prophase
In contrast, all [?] have multiple linear chromosomes.
eukaryotic cells
Circular DNA molecules also occur in [?], which are present in almost all eukaryotic cells, and in [?], which are present in plants and some unicellular eukaryotes.
mitochondria
chloroplasts
Nuclear membrane breaks down
Prophase
DNA condensing to form chromosomes (each consisting of two identical chromatids)
Prophase
Newly formed scaffold of spindle tubules attached to chromosomes at the centromere
Metaphase
Chromosomes are manoeuvred into the equator
Metaphase
Spindle tubules contract and pull the chromatids apart towards opposite poles of the cell
Anaphase
Spindle tubules break down
Telophase
Nuclear membrane re-forms
Telophase
Cell undergoes cytokinesis
Telophase
Chromosomes de-condense and disappear
Telophase
Identical diploid daughter cells
Telophase
In contrast to other cell organelles, the size of chromosomes shows a remarkable variation depending upon the [?] of cell division.
stages
: sister chromatids are replicated, thinnest
Interphase
Growth 1 phase - S-phase/Synthesis - Growth 2 phase
Interphase
Chromatin phase/Intermediate phase/Preparation phase
Interphase
Duplication of the organelle (ribosome, centrioles, centrosome, mitochondria)
Interphase
Double contents
Interphase
: Condensation/coiling: there is a progressive decrease in their length accompanied with an increase in thickness
Prophase
Breakdown of nuclear membrane due to the release of nuclear contents and chromosomes
Prophase
: Chromosomes are the most easily observed and studied during (?) when they are very thick, quite short and well spread in the cell
Metaphase
lining in the equatorial plate; chromosomes aligned in the middle along with the microtubules from the centrosome
Metaphase