Dynein and kinesin are motor proteins that play essential roles in chromosome dynamics by facilitating the intracellular transport of chromosomes along microtubules. Dynein moves chromosomes toward the nucleus by binding to adaptor proteins and walking toward the minus end of microtubules. Kinesin moves chromosomes away from the nucleus by binding to adaptor proteins and walking toward the plus end. Adaptor proteins link the motor proteins to chromosomes. Dynein and kinesin attachment allows precise control over chromosome positioning during processes like cell division and DNA repair.

1. Cell Biology:
Cell Division
Dr. Amit Joshi
HOD & Assistant Professor
Biochemistry Department
KALINGA UNIVERSITY
Naya Raipur, CG, INDIA-492101

27. Chromosome segregation
• Chromosome dynamics in eukaryotic cells involve the movement and
positioning of chromosomes within the nucleus during various cellular
processes, such as cell division, gene expression, and DNA repair.
Dynein and kinesin are two motor proteins that play essential roles in
these processes by facilitating the intracellular transport of chromosomes
along microtubules. Here's an explanation of how dynein and kinesin
work to regulate chromosome dynamics:
• Microtubules and Chromosomes:
• Microtubules are structural components of the cytoskeleton, consisting of
tubulin protein subunits arranged in a cylindrical fashion. They form a network
of tracks within the cell, serving as highways for intracellular transport.
• Chromosomes are large, thread-like structures composed of DNA and associated
proteins. During various cellular processes, such as mitosis and meiosis,
chromosomes need to be moved, aligned, and organized within the cell.

28. Dynein & Kinesin
Dynein:
• Dynein is a motor protein that moves towards the minus (-) end of microtubules, which is typically located
near the cell's centrosome (a microtubule-organizing center).
• In the context of chromosome dynamics, dynein plays a crucial role in moving chromosomes toward the
cell's nucleus or centrosome.
• Dynein binds to specific cargo adaptors or proteins associated with chromosomes. These adaptors link
dynein to the chromosome, allowing it to "walk" along microtubules.
• As dynein moves along microtubules towards the minus end, it exerts force on the chromosome, pulling it
in the direction of the centrosome or nucleus.
• Dynein is also involved in other cellular processes, such as the positioning of the mitotic spindle during
cell division.
Kinesin:
• Kinesin is another motor protein, but it moves towards the plus (+) end of microtubules, which typically
extends toward the cell's periphery.
• In chromosome dynamics, kinesin plays a role in moving chromosomes away from the nucleus or
centrosome to other regions of the cell.
• Kinesin, like dynein, binds to cargo adaptors or proteins associated with chromosomes and walks along
microtubules, exerting force on the chromosome.
• This movement helps position chromosomes in specific cellular locations, such as the periphery during
interphase or at the spindle poles during mitosis.

31. Attachment of Motor Proteins:
• Motor proteins like dynein and kinesin are typically attached to their
cargo or cellular structures through adaptor proteins.
• Adaptor proteins serve as linkers between the motor protein and the
cargo to be transported. They recognize specific binding sites on the
motor protein and cargo, facilitating their interaction.
• For example, in the context of chromosome dynamics, adaptor
proteins may bind to specific regions on chromosomes or other
cellular structures and, in turn, interact with dynein or kinesin.

32. • Dynein Attachment to Chromosomes:
• Dynein typically binds to chromosomes through adaptor proteins that link it to specific
chromosomal regions or structures.
• One well-known adaptor protein involved in dynein-chromosome interactions is called
"NUDE," which is also known as "LIS1" (Lissencephaly-1 protein). LIS1 binds to dynein and
connects it to chromosomal regions.
• Dynein can also interact with kinetochores, specialized protein structures located on the
centromere of each chromosome during cell division. Dynein helps regulate the movement and
positioning of chromosomes by attaching to kinetochores.
• Dynein's attachment to chromosomes is critical for processes such as chromosome segregation
during cell division and positioning of chromosomes within the nucleus.
• Kinesin Attachment to Chromosomes:
• Kinesin motor proteins also attach to chromosomes through adaptor proteins that facilitate the
interaction.
• The specific adaptors and binding sites for kinesin on chromosomes can vary depending on the
cellular context and the type of kinesin involved.
• For example, during mitosis, kinesin-5 (also known as Eg5) plays a role in the separation of
centrosomes and the positioning of spindle poles. It can attach to microtubules near the
centrosomes and contribute to chromosome alignment and segregation.
• Other kinesin family members may interact with chromosomal structures during different phases
of the cell cycle or for specific cellular processes.

33. ADAPTER PROTEINS OF
KINETOCHORE
•
There are several adapter proteins that play roles in attaching motor proteins like dynein and kinesin to chromosomes or
chromosomal structures. The specific adapter proteins involved can vary depending on the cellular context and the function being
performed. Here are a few examples of adapter proteins that are known to interact with chromosomes:
• NUDE (LIS1): NUDE, also known as LIS1 (Lissencephaly-1 protein), is an adapter protein that links dynein to chromosomal
regions. It plays a role in the regulation of dynein's interaction with chromosomes during processes such as chromosome
segregation.
• Dynactin: Dynactin is a multisubunit protein complex that interacts with dynein. It helps anchor dynein to cargo, which can include
chromosomes and other cellular structures. Dynactin helps in the process of dynein-mediated intracellular transport.
• CENP-E (Centromere-associated protein E): CENP-E is a kinesin-like motor protein that plays a role in mitosis. It interacts with
kinetochores, specialized chromosomal structures located at the centromere. While CENP-E is itself a motor protein, it also serves
as an adapter protein by binding to kinetochores and facilitating chromosome movement during cell division.
• Ndc80 Complex: The Ndc80 complex is another group of proteins associated with kinetochores. It functions as a microtubule-
binding adapter, connecting kinetochores to microtubules. While it is not a motor protein itself, it plays a critical role in the
attachment of kinetochores to microtubules, which is essential for chromosome segregation.
• BicD (Bicaudal D): BicD is an adapter protein that interacts with dynein and is involved in various cellular processes, including the
positioning of nuclei and chromosomes. It helps tether dynein to specific cargo, including chromosomal structures.
• RanGTP (Ran Guanosine Triphosphate): RanGTP is a small GTPase that regulates the binding of importin β to nuclear
localization signals (NLS) on cargo proteins, including proteins associated with chromosomes. This process is crucial for the
transport of various proteins, including those involved in chromosome dynamics, between the nucleus and cytoplasm.

37. Apoptosis
• Apoptosis, often referred to as programmed cell death, is a highly
regulated process that plays a crucial role in various biological
processes, including tissue development, homeostasis, and the
removal of damaged or unwanted cells. Here are some key points
about apoptosis:
Purpose of Apoptosis:
• Apoptosis is essential for maintaining tissue integrity, eliminating
damaged or infected cells, and shaping various developmental
processes.
• It serves as a mechanism to remove cells without causing
inflammation or damage to surrounding tissues.

38. Key Features of Apoptosis:
• Cellular shrinkage: Cells undergoing apoptosis typically shrink
and condense.
• Chromatin condensation: The cell's DNA condenses and
fragments.
• Formation of apoptotic bodies: The cell breaks into smaller,
membrane-bound vesicles called apoptotic bodies.
• Phagocytosis: Apoptotic bodies are recognized and engulfed by
neighboring cells or phagocytes (e.g., macrophages), leading to
their removal.

39. Signaling Pathways:
• Apoptosis can be initiated by extrinsic (death receptor-
mediated) or intrinsic (mitochondrial) pathways.
• Extrinsic apoptosis is triggered by external signals binding to
death receptors on the cell surface.
• Intrinsic apoptosis can be induced by cellular stress, DNA
damage, or other internal signals.

40. Execution Phase:
• Both extrinsic and intrinsic pathways converge on the activation of
caspases, a family of protease enzymes.
• Caspases cleave key cellular proteins, leading to the characteristic
changes seen in apoptotic cells.
• Initiator caspases activate downstream effector caspases, which
amplify the apoptotic signals.

41. Regulation of Apoptosis:
• Bcl-2 family proteins play a central role in regulating apoptosis.
• Anti-apoptotic Bcl-2 proteins protect cells from apoptosis, while pro-apoptotic members promote
it.
• The balance between these proteins determines the cell's susceptibility to apoptosis.
Mitochondrial Apoptosis Pathway:
• Intrinsic apoptosis often involves the release of cytochrome c from the mitochondria into the
cytoplasm.
• Cytochrome c activates caspases and initiates the apoptotic cascade.
Extrinsic Apoptosis Pathway:
• Extrinsic apoptosis is initiated by the binding of death ligands (e.g., Fas ligand or TNF-α) to death
receptors (e.g., Fas or TNF receptor) on the cell surface.
• This triggers the formation of the death-inducing signaling complex (DISC) and activates caspases.

42. Dysregulation and Disease:
• Dysregulation of apoptosis can contribute to various diseases,
including cancer (too little apoptosis) and neurodegenerative
disorders (excessive apoptosis).

44. Cell Biology:
Cancer
Dr. Amit Joshi
HOD & Assistant Professor
Biochemistry Department
KALINGA UNIVERSITY
Naya Raipur, CG, INDIA-492101