Hinteregger 1
Konstantinos Hinteregger
Prof. Higgins
BI101
6. April. 2024
Unit 4 Assignment
1. Haploid cells have half the number of chromosomes than diploid cells. In humans,
haploid cells contain 23 chromosomes. Examples of haploid cells would be sex cells like
sperm cells, egg cells, or in other words gametes. Diploid cells on the other hand have a
full set of chromosomes. This means they contain 46 chromosomes, consisting of two
sets of 23 chromosomes each. Out of these 23 chromosome pairs, 22 are autosomes,
meaning they are not related to our biological sex. Only one pair determines the sex.
Diploid cells are somatic cells, which include most cells in the body except gametes.
Karyotype is a procedure where pictures of chromosomes from a single cell are taken,
arranged, and then analyzed visually, looking for abnormalities. It can reveal missing
chromosomes, extra chromosomes, or structural abnormalities in chromosomes. This
procedure is used in medicine for research in genetic disorders, and variations in
chromosome number or structure in an individual (Amoeba Sisters 2018).
2. The analogy used to explain DNA replication is that of a zipper or pair of zippers. This
analogy represents the way DNA strands unzip and separate during replication, with each
side acting as a template for the synthesis of a new complementary strand. There are four
major enzymes used in this process: Helicase: This enzyme unwinds the double helix
structure of DNA by breaking the hydrogen bonds between the complementary base
pairs.
Hinteregger 2
•
DNA Polymerase: This enzyme replicates DNA molecules to build a new strand
of DNA by adding nucleotides complementary to the template strand.
•
Primase: This enzyme synthesizes short RNA primers on both strands of the DNA
to provide a starting point for DNA polymerase.
•
Ligase: This enzyme joins the Okazaki fragments on the lagging strand by
catalyzing the formation of phosphodiester bonds between them.
The molecules needed to assemble a DNA strand are called nucleotides. They consist of a
sugar (deoxyribose), a phosphate group, and a nitrogenous base (adenine, cytosine,
guanine, or thymine). During DNA replication the so-called Okazaki fragments, named
after a Japanese biologist, are formed. These fragments are short and newly synthesized
DNA fragments. They are named after Reiji Okazaki, who discovered them. Okazaki
fragments are significant because they represent the discontinuous synthesis of the
lagging strand and require additional processing to join them into a continuous strand.
DNA replication occurs in multiple steps:
•
DNA replication begins as the DNA helicase unwinds the double helix and forms
a replication fork where DNA replication begins.
•
The next step is called primer synthesis. Here, primase synthesizes short RNA
primers on both strands of the DNA to create a starting point for the DNA
polymerase.
•
This is followed by elongation. In this step, the DNA polymerase adds nucleotides
to the growing DNA strand, using the template strand as a guide. The leading
strand is synthesized continuously in the direction from 5' to 3', while the lagging
strand is synthesized discontinuously in the form of Okazaki fragments.
Hinteregger 3
•
The process continues with the removal of the primer and the joining of the
fragments. The DNA polymerase removes the RNA primers and replaces them
with DNA nucleotides. The DNA ligase assembles the Okazaki fragments on the
remaining strand to form a continuous DNA strand.
•
DNA replication ends when the DNA polymerase reaches the end of the DNA
molecule or encounters an obstacle (Amoeba Sisters 2014).
3.
•
Single chromosome:
i. These are individual, unreplicated chromosomes consisting of a single
DNA molecule. They are visible during certain stages of the cell cycle,
such as mitosis and meiosis.
•
Double chromosome
i. Double chromosomes are referred to as replicated chromosomes. Each
chromosome consists of two identical sister chromatids joined together at
the centromere. They are visible during certain stages of the cell cycle,
such as mitosis and meiosis, specifically during metaphase.
•
Sister chromatids
i. Sister chromatids are two identical copies of a single chromosome
produced by DNA replication. They are held together by a centromere and
are considered to be double chromosomes. Sister chromatids are visible
during certain stages of the cell cycle, such as mitosis and meiosis,
specifically during metaphase.
Hinteregger 4
•
Chromatin
i. Chromatin is a complex of DNA and proteins, including histones, that
forms chromosomes within the nucleus of eukaryotic cells. It exists in a
less condensed state during interphase, allowing for gene expression and
DNA replication.
Histone proteins are crucial as they help to bind and package the DNA into an even
smaller and more compact structure. In the case of chromatin, histones aid in the winding
of DNA into nucleosomes, which are the basic units of chromatin. During chromosome
formation, histones contribute to the further condensation of chromatin into visible
chromosomes, facilitating proper segregation during cell division. Structures present in
cells that are in interphase include chromatin, which exists in a less condensed state
compared to chromosomes. During interphase, chromosomes are not visible as distinct
entities, and the nucleus contains a complex network of chromatin, along with various
organelles and structures involved in cellular processes such as transcription, translation,
and metabolism (Smart culture education 2021; Stated Clearly 2017).
4. The cell cycle of a eukaryotic organism consists of several major stages: interphase,
mitosis, and cytokinesis.
•
Interphase: During interphase, the cell prepares for division by growing, carrying
out its normal functions, and duplicating its DNA.
•
Mitosis: Mitosis is the process of nuclear division, where the duplicated DNA is
evenly distributed into two daughter nuclei. Mitosis consists of several phases:
prophase, metaphase, anaphase, and telophase.
Hinteregger 5
•
Cytokinesis: Cytokinesis is the division of the cytoplasm and other organelles,
resulting in two daughter cells.
There are several checkpoints throughout this process. These checkpoints monitor the
cellular conditions and ensure that processes are completed accurately. The cell must pass
these checkpoints to get into the next stage. The DNA is replicated during the so-called SPhase of interphase. During this phase, the cell duplicates its genetic code to ensure every
daughter cell receives a full set of chromosomes (Stated Clearly 2017).
5. Mitosis is the process of cell division that results in the formation of two identical
daughter cells. It consists of several stages, each with distinct events. Mitosis starts with
Prophase. During this process, DNA is condensed into visible chromosomes,
microtubules form from the centromere, and the nucleus disappears. The next phase is
called Prometaphase. In this phase, the nuclear membrane breaks down. Furthermore,
spindle fibers attach to the kinetochores on the chromosomes. Metaphase is next. In this
phase, the chromosomes align along the cell’s equator. Next is the Anaphase. During this
phase, sister chromatids are separated and pulled to the opposite side of the cell. In
charge of pulling the chromatids apart are the microtubules. Following Anaphase is
Telophase. During Telophase new nuclear membrane forms around separated
chromosomes. Furthermore, chromosomes uncoil and return to their uncondensed state.
Cytokinesis is the process of dividing the cytoplasm and organelles between the two
daughter cells.
•
Prophase:
i. DNA condenses into visible chromosomes.
ii. Microtubules (spindle fibers) form from the centrosomes.
Hinteregger 6
iii. The nucleolus disappears.
•
•
Prometaphase:
i.
The nuclear membrane breaks down.
ii.
Spindle fibers attach to the kinetochores on the chromosomes.
Metaphase:
i.
•
•
Chromosomes align along the cell's equator (metaphase plate).
Anaphase:
i.
Sister chromatids separate and move towards opposite poles of the cell.
ii.
Microtubules shorten, pulling chromatids apart.
Telophase:
i.
New nuclear membranes form around separated chromosomes.
ii.
Chromosomes uncoil and return to their uncondensed state.
iii.
Spindle fibers disassemble.
During the Prophase in a human cell, there are double chromosomes, each chromosome
consists of two chromatids. In Prometaphase, Metaphase, Anaphase, and Telophase, there
are double chromosomes and single chromosomes (as chromatids separate). During
Cytokinesis, each daughter cell receives a complete set of single chromosomes (NDSU
VCell 2011).
6. During the cell cycle of a eukaryotic cell there are three checkpoints.
•
G1 Checkpoint: Occurs before entry into S Phase
•
G2 Checkpoint: Occurs before entry into mitosis (M Phase)
•
G3 Checkpoint: Occurs during metaphase of mitosis
Hinteregger 7
The function of these checkpoints is to make sure the cell is ready to proceed to the next
stage of the cell cycle. If a cell fails to pass one of these checkpoints, it may undergo
apoptosis (programmed cell death) or enter a state of dormancy. Mutations can modify
checkpoints by affecting the genes that regulate cell cycle progression. For example,
mutations in tumor suppressor genes or proto-oncogenes can disrupt the normal
functioning of checkpoints, leading to uncontrolled cell division and the development of
cancerous cells. The video mentions the G1 checkpoint as the most important in tumor
suppression. At this checkpoint, the cell evaluates various factors such as DNA integrity,
nutrient availability, and external signals before deciding whether to proceed with cell
division (Prof. Dave Explains 2016).
7. Binary fission is the process by which prokaryotic organisms like bacteria divide and
reproduce. The difference between Binary fission and mitosis is that Binary fission
occurs in prokaryotic cells, while mitosis happens in eukaryotic cells. At the end of both
cycles, the two cells produced are essentially identical. Steps of binary fission:
•
Growth: The bacterial cell grows to a sufficient size to divide into two new cells.
•
DNA replication: The cell replicates its large circular strand of DNA and its
plasmids
•
Movement of genetic material: The replicated DNA strands move to opposite
ends of the cell.
•
Formation of new cell wall: A new cell wall forms between the two DNA strands.
•
Separation: The cell wall fully forms, allowing the two halves of the cell to
separate into two new bacterial cells (Cognito 2022).
Hinteregger 8
8.
•
Meiosis I:
i. Prophase I:
1. DNA condenses to form chromosomes.
2. Homologous chromosomes pair up and undergo synapsis.
3. Crossing over occurs, leading to recombination between
chromatids.
4. Nuclear membrane breaks down.
5. Centrosomes migrate to opposite ends, microtubules appear, and
attach to chromosomes.
ii. Metaphase I:
1. Paired homologous chromosomes align randomly at the equator of
the cell.
iii. Anaphase I:
1. Homologous chromosomes separate and migrate to opposite poles
of the cell.
2. Sister chromatids remain attached at their centromeres.
iv. Telophase I and Cytokinesis:
1. Cell divides into two daughter cells, each with half the amount of
DNA as the parent germ-line cell.
v. Meiosis II: 5. Prophase II:
1. Chromosomes condense, nuclear envelope breaks down, and
spindle apparatus forms.
Hinteregger 9
2. Daughter cells have only one copy of each homologous
chromosome.
vi. Metaphase II:
1. Chromosomes align at the equator of the cell, with random
alignment.
vii. Anaphase II:
1. Sister chromatids are pulled apart as microtubules shorten.
2. Ends of the cell are pushed further apart as microtubules elongate.
viii. Telophase II and Cytokinesis:
1. Nuclear membrane reforms and cytoplasm divides into two haploid
daughter cells.
Differences and Similarities
•
Meiosis I vs. Mitosis:
i.
Meiosis I involves pairing and synapsis of homologous chromosomes, as
well as crossing over, which does not occur in mitosis.
ii.
Mitosis results in two identical daughter cells, while Meiosis I results in
two unique daughter cells with half the DNA content.
•
Meiosis II vs. Mitosis:
i.
Meiosis II and mitosis are similar in that they both involve separation of
sister chromatids.
ii.
However, in Meiosis II, the starting cells already have half the DNA
content, whereas in mitosis, the starting cell is diploid.
Hinteregger 10
•
End Cells of Meiosis vs. Mitosis:
i.
At the end of meiosis, there are four unique haploid cells (gametes),
each with one copy of each chromosome.
ii.
At the end of mitosis, there are two identical diploid cells, each with two
copies of each chromosome (NDSU VCell 2012).
9.
•
Sexual Reproduction
i. Involves the fusion of gametes (sperm and egg) from two parents.
ii. Genetic variation is introduced through the combination of genetic
material from two different individuals.
iii. Offspring are genetically unique from their parents and siblings.
iv. Examples include humans, animals, most plants, and some fungi.
•
Asexual Reproduction
i. Involves the production of offspring from a single parent organism.
ii. No fusion of gametes occurs, and genetic material is not exchanged.
iii. Offspring are genetically identical or nearly identical clones of the parent
organism.
iv. Examples include bacteria, some fungi, plants (through methods like
budding or fragmentation), and some animals (like certain species of
worms and insects).
Hinteregger 11
Advantages and Disadvantages of Sexual and Asexual Reproduction
•
Advantages of Sexual Reproduction
i.
Increases genetic diversity within a population, which can enhance
adaptability to changing environments.
ii.
Allows for the removal of harmful mutations through genetic
recombination.
iii.
Facilitates the development of advantageous traits through natural
selection.
•
Disadvantages of Sexual Reproduction
i.
Requires the energy and time investment of finding a mate and
producing gametes.
ii.
Risk of producing offspring with deleterious mutations or genetic
disorders.
iii.
Slower population growth compared to asexual reproduction due to the
need for two parents.
•
Advantages of Asexual Reproduction
i.
Efficient and rapid population growth since only one parent is needed.
ii.
Guarantee of passing on beneficial traits to offspring without the dilution
of genetic material.
iii.
Suitable for stable environments where offspring are well-adapted to
existing conditions.
Hinteregger 12
•
Disadvantages of Asexual Reproduction
i.
Lack of genetic diversity makes populations more susceptible to
environmental changes or diseases.
ii.
Inability to eliminate harmful mutations without the genetic
recombination that occurs in sexual reproduction.
iii.
Limited ability to generate novel genetic combinations, which may
hinder long-term adaptability (Bozeman Science 2013).
10.
•
Diploid Dominant
i. In a diploid dominant life cycle, the multicellular organism spends most of
its life in the diploid state.
ii. Haploid cells are only produced during the process of gamete formation
for sexual reproduction.
iii. Examples of organisms with diploid dominant life cycles include humans,
animals, and most fungi.
•
Haploid Dominant
i. In a haploid-dominant life cycle, the multicellular organism spends the
majority of its life in the haploid state.
ii. Diploid cells are only briefly formed during the fusion of gametes for
sexual reproduction.
iii. Examples of organisms with haploid dominant life cycles include some
fungi, algae, and certain types of plants like mosses and liverworts.
Hinteregger 13
•
Alternating Life Cycles
i. In an alternating life cycle, the organism alternates between diploid and
haploid phases, with each phase being multicellular.
ii. Both diploid and haploid phases can be structurally and functionally
distinct.
iii. Examples of organisms with alternating life cycles include certain types of
algae, some fungi, and plants like ferns and some types of seaweed.
Advantages and Disadvantages:
•
Advantages of Diploid Dominant Life Cycles:
i. Greater genetic stability due to the presence of two copies of each
chromosome.
ii. Provides a backup copy of genes, reducing the impact of harmful
mutations.
iii. Allows for complex development and specialization of cell types in
multicellular organisms.
•
Disadvantages of Diploid Dominant Life Cycles:
i. Requires the investment of energy and resources in maintaining diploid
cells throughout the organism's life.
ii. Limits the potential for genetic diversity within a population, which may
hinder adaptability to changing environments.
•
Advantages of Haploid Dominant Life Cycles:
i. Energy-efficient as only one set of chromosomes needs to be replicated
and maintained.
Hinteregger 14
ii. Facilitates rapid reproduction and dispersal of offspring.
iii. Increases genetic diversity through genetic recombination during meiosis.
•
Disadvantages of Haploid Dominant Life Cycles:
i. Reduced genetic stability due to the absence of backup copies of genes.
ii. Higher susceptibility to deleterious mutations and environmental stressors.
iii. Limited development and specialization of cell types in multicellular
organisms (Amoeba Sisters 2017).
Hinteregger 15
Works Cited
Amoeba Sisters. “Chromosomes and Karyotypes.” YouTube, 4 Apr. 2018,
www.youtube.com/watch?v=mBq1ULWJp_M, Accessed 6 Apr. 2024.
Amoeba Sisters. “(OLD VIDEO) DNA Replication: The Cell’s Extreme Team Sport.” YouTube,
16 June 2014, www.youtube.com/watch?v=5qSrmeiWsuc, Accessed 6 Apr. 2024.
Smart culture education. “What Is the Difference between Chromosomes and Chromatin?”
Www.youtube.com, 30 Aug. 2021,
www.youtube.com/watch?v=IHlPb5MYvjo&list=PLfQf5Axy67ppzgueJW5ump508Snys
YcAL&index=5&t=87s . Accessed 6 Apr. 2024.
Stated Clearly. “What Is a Chromosome?” YouTube, YouTube Video, 26 July 2017,
www.youtube.com/watch?v=IePMXxQ-KWY . Accessed 6 Apr. 2024.
NDSU VCell . “Mitosis.” Www.youtube.com, 4 Aug. 2011,
www.youtube.com/watch?v=C6hn3sA0ip0&list=PLfQf5Axy67ppzgueJW5ump508Snys
YcAL&index=7 . Accessed 6 Apr. 2024.
Prof. Dave Explains . “What Is Cancer?” Www.youtube.com, 29 Sept. 2016,
www.youtube.com/watch?v=TUuxT388_zM&list=PLfQf5Axy67ppzgueJW5ump508Sny
sYcAL&index=8&t=193s . Accessed 6 Apr. 2024.
Cognito. “Binary Fission - How Do Bacteria Divide? #12.” Www.youtube.com, 10 Apr. 2022,
www.youtube.com/watch?v=kKiz8Wzcfc8&list=PLfQf5Axy67ppzgueJW5ump508Snys
YcAL&index=9 . Accessed 6 Apr. 2024.
NDSU VCell. “Meiosis.” Www.youtube.com, 16 July 2012, www.youtube.com/watch?v=DLGfd-Wpr4&list=PLfQf5Axy67ppzgueJW5ump508SnysYcAL&index=10 . Accessed
6 Apr. 2024.
Hinteregger 16
Bozeman Science . “Diploid vs. Haploid Cells.” Www.youtube.com, 2 Mar. 2013,
www.youtube.com/watch?v=zglQ2Ildw4I&list=PLfQf5Axy67ppzgueJW5ump508SnysY
cAL&index=12 . Accessed 6 Apr. 2024.
Sisters, Amoeba. “Asexual and Sexual Reproduction.” Www.youtube.com, 20 July 2017,
www.youtube.com/watch?v=fcGDUcGjcyk&list=PLfQf5Axy67ppzgueJW5ump508Snys
YcAL&index=12 . Accessed 6 Apr. 2024.