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
nuclear membrane starts to form again; contents in the middle of the cell
Metaphase
: chromosomes are smallest
Anaphase
pulling apart of chromosomes into chromatids; spindle fiber separates to the opposite pole; microtubules are still visible
Anaphase
Therefore, chromosomes measurements are generally taken during mitotic [?]
metaphase
: microtubules are not prominent anymore and on the far side of the opposite pole
Telophase
nuclear membrane and the cytoplasm starts to reform again
Telophase
chromosome is not visible anymore
Telophase
has loose chromatin structure and active for transcription.
• Euchromatin
has condensed chromatin structure and is inactive for transcription.
• Heterochromatin
The major components of chromatin are
DNA and histone proteins.
two types of chromatin can be distinguished:
• [?], which consists of DNA that is active, e.g., being expressed as protein.
Euchromatin
• [?], which consists of mostly inactive DNA.
Heterochromatin
We have [?] with [?] and not all are active
3B bases
20,000 genes
- May convert to euchromatin through acetylation or demethylation
Facultive Heterochromatin
- Constitutive heterochromatin
Centromeres
- Double stranded DNA
Centromeres
- Binds to Kinetochore during mitosis
Centromeres
- Constitutive heterochromatin
Telomere
- Single stranded DNA
Telomere
- Protect ends of DNA from degradation
Telomere
- prevents chromosomes from sticking together
Telomere
The DNA of eukaryotic cell is tightly bound to small basic proteins (?) that package the DNA in an orderly way in the cell nucleus.
histones
For e.g., the total extended length of DNA in a human cell is nearly 2 m, but this must be fit into a nucleus with a diameter of only [?].
5 to 10um
The major proteins of chromatin are the
histones
– small proteins containing a high proportion of basic amino acids (arginine and lysine) that facilitate binding negatively charged DNA molecule .
histones
There are 5 major types of histones:
H1, H2A, H2B, H3 and H4
- which are very similar among different species of eukaryotes.
H1, H2A, H2B, H3 and H4
: enables the chromosome to bend
primary constriction
point of attachment for kinetochore and microtubules
primary constriction
: constrictions found in the arm for identification
secondary constriction
The two ends of a chromosome are known as
telomeres
It required for the replication and stability of the chromosomes
telomeres
They help the organise each of our 46 chromosomes in the nucleus
They protect the ends of our chromosomes by forming a cap, much like the plastic tip on shoelaces.
telomeres
If the [?] were not there, our chromosomes may end up sticking to other chromosomes.
telomeres
Every time a cell carries out DNA replication the chromosomes are shortened by about [?] (A, C, G, or T) per replication.
25-200 bases
However, because the ends are protected by telomeres, the only part of the chromosome that is lost, is the [?], and the DNA is left undamaged.
telomere
Without [?], important DNA would be lost everytime a cell divides.
telomeres
are made of repetitive sequences of noncoding DNA that protect the chromosome from damage.
Telomeres
Each time a cell divides, the [?] become shorter.
telomeres
Eventually, the [?] become so short that the cell can no longer divide.
telomeres
length determines the person’s age
telomeres
The region where two sister chromatids of a chromosome appear to be joined or “held together” during mitotic phase is called
Centromere
When chromosomes are stained they typically show a dark-stained region that is the centromere.
Centromere
Also termed as Primary constriction
Centromere
During mitosis, the [?] that is shared by the sister chromatids must divide so that the chromatids can migrate to opposite poles of the cell.
Centromere
Therefore, the [?] is an important component of chromosome structure and segregation.
Centromere
The [?] divides the chromosome into two arms, so that, for example, an acrocentric chromosome has one short (p) and one long arm (q arm).
centromere
The [?] is named for “petit” meaning ‘small’
p arm
is named q simply because it follows p in the alphabet.
q arm
has arms of equal length.
metacentric chromosome
All house mouse chromosomes are [?]
acrocentric
human chromosomes include both [?], but no [?].
metacentric and acrocentric
telocentric
Chromosome Types: Based on
Centromere Position
• Centromere is located exactly at the centre of chromosome, i.e. both arms are equal in size
Metacentric Chromosome
Such chromosomes assume „V‟ shape at anaphase.
Metacentric Chromosome
• The centromere is located on one side of the centre point such that one arm is longer than the other
Submetacentric Chromosome
• These chromosomes become „J‟ or „L‟ shaped at anaphase
Submetacentric Chromosome
• Centromere is located close to one end of the chromosome and thus giving a very short arm and a very long arm.
Acrocentric Chromosome
• These chromosomes acquire ‘J’ shape or rod shape during anaphase. s are „I‟ shaped or rod shaped.
Acrocentric Chromosome
• Centromere is located at one end of the chromosome so that the chromosome has only one arm.
Telocentric Chromosome
• These chromosome are „I‟ shaped or rod shaped.
Telocentric Chromosome
Within the [?] region, most species have several locations where spindle fibers attach, and these sites consist of DNA as well as protein.
centromere
The actual location where the attachment occurs is called the [?] and is composed of both DNA and protein
kinetochore
Human cells are [?] (46 Ch or 2n)
diploid
Autosome (body cells : diploid):
22 pairs
Sex chromosome (sex cells : haploid):
1 pair
first three: [?] centromere (equal size of both arms)
metacentric
The size of the chromosomes in mitotic phase of animal and plants sp generally varies between [?] in length, and between [?] in diameter.
0.5 m and 32 u
0.2 u and 3.0 u
The longest metaphase chromosomes found in Trillium -[?].
32 u
The giant chromosomes found in diptera and they may be as long as [?] and up to [?] in diameter.
300 u
10 u
In general, plants have [?] than animal and species having lower chromosome numbers have long chromosomes than those having higher chromosome numbers.
longer chromosomes
is a test to identify and evaluate the size, shape, and number of chromosomes in a sample of body cells.
Karyotype
[?] of chromosome pieces, can cause problems with a person’s growth, development, and body functions.
Extra or missing chromosomes, or abnormal positions
It is usually represented by a diagram called idiogram
Karyotype
where chromosomes of haploid set of an organism are ordered in a series of decreasing size
idiogram
Human chromosomes are divided into
7 groups & sex chromosomes
A: [?] Large metacentric
1-3
B: [?] Large submetacentric
4,5
C: [?], X Medium sized, metacentric and submetacentric
6-12
D: [?] medium-sized acrocentric plus satellites
13-15
E: [?] short metacentric 16 or submetacentric 17,18
16-18
F: [?] Short metacentrics
19-20
G: [?], Y Short acrocentrics with satellites
21,22
: no satellites
Y
extra chromosome 21st (47 chromosomes)
Down Syndrome - Trisomy 21
lacks X chromosome
Turner Syndrome
excess X chromosome
Klinefelter Syndrome
• To see chromosomes by microscope, they are normally treated with chemical dyes, such as Giemsa.
Chromosome banding
• The chromosome will appear as a series of alternate dark and light bands.
Chromosome banding
• If Giemsa is used, the dark band is called [?] and the light band is named [?].
G-band or G-positive band,
G-negative band
• a technique for the identification of chromosomes and its structural abnormalities
Chromosome banding
Human
46
Chimpanzee
48
Dog
78
Horse
64
Chicken
78
Goldfish
94
Fruit fly
8
Mosquito
6
Nematode
11(m), 12(f)
Horsetail
216
Sequoia
22
Round worm
2
Transcriptionally active
Euchromatin,
Transcriptionally inactive
Heterochromatin,
DNA is loosely packed
Euchromatin,
DNA is highly packed
Heterochromatin,
Actively present in Prokaryotic and eukaryotic genome
Euchromatin,
Only present in eukaryotic genome
Heterochromatin,
Genetically active
Euchromatin,
Genetically inactive
Heterochromatin,
Present at inner side of the nucleus
Euchromatin,
Present at nucleus periphery
Heterochromatin,
Stained lighter
Euchromatin,
Stained dark
Heterochromatin,
Early replicative
Euchromatin,
Late replicative
Heterochromatin,
Aren’t sticky
Euchromatin,
Are usually sticky
Heterochromatin,
Allow gene to form a protein
Euchromatin,
Regulates genetic integrity, and control gene expression
Heterochromatin,
Low genetic density
Euchromatin,
High genetic density
Heterochromatin,
Consist 2 to 3% part of the genome
Euchromatin,
Consist 97 to 98% part of the genome
Heterochromatin,
