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Final Time!!! Flashcards

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1
Q

What is the basic mechanism behind exon duplication?

A

Unequal crossing over during meiosis

This process can lead to the generation of recombinant chromosomes with varying numbers of exons.

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2
Q

Define a gene.

A

The entire nucleic acid sequence necessary for the synthesis of a functional gene product

This includes protein-coding, enhancer, and promoter regions.

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3
Q

What percentage of human DNA encodes proteins and functional RNAs?

A

About 1.5 percent

The remainder includes regulatory sequences that control gene expression and introns.

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4
Q

What are the three types of gene duplication outcomes?

A
  • Redundancy
  • Neofunctionalization
  • Subfunctionalization

These outcomes can lead to evolutionary innovations.

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5
Q

What is a simple transcription unit?

A

A monocistronic region extending from the 5′ cap site to the 3′ poly(A) site with introns removed

It encodes one protein and represents about 10% of human transcripts.

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6
Q

What is the difference between homologs, orthologs, and paralogs?

A
  • Homologs: evolved from a common ancestor
  • Orthologs: same function, differ due to speciation
  • Paralogs: differ due to gene duplication

These terms describe relationships between genes across different species.

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7
Q

What does the histone code represent?

A

Specific post-transcriptional modification combinations in different chromatin regions

This influences chromatin function by creating or removing chromatin-associated protein binding sites.

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8
Q

What is the role of telomeres?

A

Protect chromosome ends from degradation

They play a crucial role in maintaining genomic stability.

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9
Q

What is epigenetics?

A

Inheritance depends on factors other than DNA sequences

Examples include X-chromosome inactivation and differences in disease susceptibility between genetically identical twins.

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10
Q

What is the packing ratio of DNA in nucleosomes?

A

Approximately 7:1

This ratio increases significantly with higher levels of chromatin structure.

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11
Q

What is heterochromatin?

A

Highly condensed interphase chromatin that is essentially inactive and without transcription

It is concentrated around the centromere and telomeres of chromosomes.

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12
Q

What is the function of nucleosomes?

A

The lowest level of chromosome organization, consisting of DNA wrapped around histone proteins

Nucleosomes help in compacting DNA and regulating access to genetic information.

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13
Q

What is the structure of a nucleosome core particle?

A

Histone octamer with 147bp of DNA coiled around it

The octamer consists of two molecules each of histones H2A, H2B, H3, and H4.

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14
Q

What are intermediate filaments?

A

Structural components that provide support and shape to cells

They are part of the cytoskeleton and play a role in maintaining cell integrity.

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15
Q

True or false: Euchromatin is transcriptionally inactive.

A

FALSE

Euchromatin represents transcriptionally active regions of chromosomes.

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16
Q

What is the function of chromatin-remodeling complexes?

A

Regulate compaction of chromatin by sliding DNA associated with octamers

They hydrolyze ATP to facilitate changes in chromatin structure.

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17
Q

What is the ultimate in chromatin compactness?

A

Mitotic chromosomes

They represent a packing ratio of 10,000:1.

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18
Q

What does epigenetics refer to in the context of inheritance?

A

Inheritance depends on factors other than DNA sequences

Example: X-chromosome inactivation can occur even with identical DNA sequences.

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19
Q

What is an example of X-chromosome inactivation?

A

One X chromosome is inactivated while the other is not

This can occur despite identical DNA sequences.

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20
Q

Can an epigenetic state be reversed?

A

Yes, it can usually be reversed

X chromosomes are reactivated prior to the formation of gametes.

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21
Q

What may differences in disease susceptibility and longevity between genetically identical twins be attributed to?

A

Epigenetic differences that appear as they age

These differences can influence health outcomes.

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22
Q

What determines the chemical modifications found in newly synthesized histones?

A

Parental histones

This influences the epigenetic state of the daughter cells.

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23
Q

What is the heterochromatin epigenetic code memory?

A

Histone octamers di- or trimethylated at H3 lysine 9 are distributed to daughter chromosomes

This process regenerates heterochromatin in both daughter chromosomes.

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24
Q

What are the three types of DNA sequences required for a long linear DNA molecule to function as a chromosome?

A
  • Telomeres
  • Centromeres
  • Origins of replication

These sequences are essential for chromosome function.

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25
What is the role of **telomerase**?
Preserves linear chromosome ends during replication ## Footnote It synthesizes DNA from an RNA template.
26
What is the **structure** of the eukaryotic chromosome?
Most human cells are diploid, containing one maternal and one paternal copy of each chromosome ## Footnote Males have one set of non-homologous sex chromosomes (X and Y).
27
What is the **nucleus** described as in terms of organization?
An organized organelle ## Footnote Chromatin fibers are concentrated into distinct territories.
28
What are **transcription factories**?
Nuclear sites where genes are physically moved for transcription ## Footnote These sites contain transcription machinery.
29
What is a **telomere**?
The end of each chromosome, distinguished by repeated sequences ## Footnote Telomeres protect chromosome ends from degradation.
30
What happens to **telomere lengths** in somatic cells?
They are reduced with each cell division ## Footnote This limits cell doublings and growth.
31
What occurs when telomeres shorten to a critical point?
Cells stop their growth and division ## Footnote This is a mechanism to limit cellular aging.
32
What is the significance of **telomerase activity** in cells?
Cells that resume telomerase expression continue to proliferate ## Footnote These cells do not show normal signs of aging.
33
What percentage of human tumors have cells with **active telomerase**?
Approximately 90% ## Footnote This is associated with uncontrolled cell division.
34
What is a **centromere**?
The site markedly indented on a chromosome ## Footnote It contains constitutive heterochromatin and is crucial for mitosis.
35
What is the function of **centromeric DNA**?
Site of microtubule attachment during mitosis ## Footnote DNA sequence is not important for centromere structure and function.
36
What are the **four phases** of the eukaryotic cell cycle?
* M phase (Mitotic) * G1 phase * S phase * G2 phase ## Footnote The eukaryotic cell cycle includes these phases for cell growth, DNA replication, and division.
37
What is the role of **telomeres** in the cell cycle?
Protect the ends of chromosomes from degradation ## Footnote Telomeres are added by telomerase and are crucial for complete chromosome replication.
38
True or false: **G0 cells** are always mitotically active.
FALSE ## Footnote G0 cells are often terminally differentiated and have lost the ability to divide.
39
What occurs during the **G1 phase** of the cell cycle?
* Cell growth * High biosynthetic activity * Variable duration depending on cell type ## Footnote Cells may exit to G0 phase during this stage.
40
What is the primary function of **S phase** in the cell cycle?
DNA synthesis and chromosome replication ## Footnote RNA transcription and protein synthesis are greatly reduced during this phase.
41
What happens during **anaphase** of mitosis?
* Kinetochore microtubules shorten * Chromosomes move poleward * Movement of poles away from each other ## Footnote Anaphase consists of two independent processes: Anaphase A and Anaphase B.
42
What are the **three major protein classes** that regulate the cell cycle control system?
* Cyclin-dependent protein kinases (Cdks) * Protein phosphatases * CDK inhibitors ## Footnote These proteins monitor cycle progress and signal whether to continue or halt the cycle.
43
What is the function of **cyclins** in the cell cycle?
Regulate the activity of cyclin-dependent kinases (Cdks) ## Footnote Cyclins are present only during specific cell cycle stages and are regulated by synthesis and degradation.
44
Fill in the blank: The **anaphase-promoting complex** (APC/C) targets proteins for degradation by _______.
proteasomes ## Footnote APC/C catalyzes key transitions in the cell cycle, including anaphase.
45
What is the role of **Cdk inhibitors (CKIs)** in the cell cycle?
Block Cdk activity ## Footnote CKIs regulate cell cycle progression by inhibiting specific cyclin-Cdk complexes.
46
What is the significance of **checkpoints** in the cell cycle?
Monitor cycle progress and ensure proper timing of transitions ## Footnote Major checkpoints occur at G1, G2, and during mitosis.
47
What occurs during **telophase** of mitosis?
* Chromosomes decondense * Nuclear membrane reassembles around chromosomes ## Footnote Telophase is followed by cytokinesis, where the cell divides into two daughter cells.
48
What is the **function of the mitotic spindle**?
Facilitates chromosome segregation during mitosis ## Footnote The mitotic spindle is composed of microtubules that attach to kinetochores.
49
What is **chromosome biorientation**?
Attachment of microtubules from both spindle poles to sister chromatids ## Footnote This allows chromosomes to be positioned in the center of the cell during prometaphase.
50
What happens during **cytokinesis**?
Division of the cell into two daughter cells ## Footnote Cytokinesis usually follows mitosis but is not strictly required.
51
What is the **G1 checkpoint** also known as?
START ## Footnote This checkpoint assesses DNA integrity before the cell transitions to the S phase.
52
What are the **three classes of microtubules** in the mitotic spindle?
* Astral MTs * Kinetochore MTs * Polar MTs ## Footnote Each class has distinct roles in chromosome movement and spindle structure.
53
What regulates **cell cycle entry** in yeast and vertebrates?
* Nutritional state (in yeast) * Presence of mitogens and anti-mitogens (in vertebrates) ## Footnote Molecular events promoting entry into the cell cycle are conserved across species.
54
What triggers **chromosome duplication** at DNA origin of replication sites?
G1/S CDKs ## Footnote These cyclin-dependent kinases are crucial for initiating DNA replication.
55
What is the role of **cohesins** during mitosis?
Link replicated DNA molecules to ensure accurate segregation ## Footnote Cohesins are essential for maintaining the integrity of sister chromatids.
56
What is assessed during the **G1-S transition** checkpoint?
DNA integrity ## Footnote This checkpoint occurs late in the G1 stage.
57
At the G1-S transition, cells can become _______.
* Quiescent * Differentiate * Make DNA repairs * Proceed to S phase ## Footnote This transition is critical for determining the cell's next steps.
58
In yeast, the G1-S transition is referred to as **START**; what is it called in multicellular eukaryotes?
Restriction point ## Footnote This is the point of irreversible commitment to division.
59
What initiates the transition at the G1-S phase?
Extracellular signals ## Footnote Nutrients for yeast and growth factor signaling for multicellular eukaryotes.
60
What is the function of **Cdh1** in the cell cycle?
Adaptor protein for the anaphase promoting complex (APC) ## Footnote Cdh1 is crucial for exit from mitosis by recruiting mitotic cyclins to the APC.
61
What does the **APC** do?
Acts as a ubiquitin ligase ## Footnote It is involved in the degradation of mitotic cyclins.
62
What stabilizes the **G1 phase**?
Degradation of mitotic cyclins ## Footnote This process is facilitated by Cdh1's action on the APC.
63
How do G1/S phase CDKs affect **Cdh1** during the S phase?
Phosphorylate Cdh1, disrupting its association with APC ## Footnote This leaves the APC inactive during the S phase and early mitotic phase.
64
What ensures that **Sic1** is fully phosphorylated and targeted for destruction?
Six suboptimal phosphorylation sites ## Footnote This mechanism ensures rapid Sic1 degradation and initiation of S phase.
65
In metazoans, entry into S phase is regulated by a mechanism similar to budding yeast but involves which protein instead of Sic1?
CKI p27 ## Footnote This highlights evolutionary conservation in cell cycle regulation.
66
What is the role of the **origin recognition complex (ORC)**?
Associated with all DNA replication origins ## Footnote It is essential for the initiation of DNA replication.
67
What initiates **unwinding of DNA** during S phase?
S phase CDKs ## Footnote These kinases are crucial for starting DNA replication.
68
What links sister chromatids during S phase?
Cohesin complex rings ## Footnote These rings tether duplicated chromosomes together.
69
During which phases are **cohesins** released from chromosome arms?
Prophase and early metaphase ## Footnote Cohesins are retained only in the region of the centromere during metaphase.
70
What is the **function of mitotic CDKs** in eukaryotes?
* Induce chromosome condensation * Induce nuclear envelope breakdown * Induce spindle formation ## Footnote Mitotic CDKs are crucial for the entry into mitosis.
71
What is the role of the **kinetochore** during mitosis?
* Attaches to microtubules from opposite spindle poles * Ensures bi-orientation of sister chromatids ## Footnote This mechanism is essential for accurate chromosome segregation.
72
What happens to **mitotic cyclins** at the completion of mitosis?
They are degraded ## Footnote This degradation allows daughter cells to enter the G1 phase.
73
Define **amphitelic attachment**.
Stable attachment of sister kinetochores to microtubules from opposite spindle poles ## Footnote This type of attachment is crucial for proper chromosome segregation.
74
What does the **spindle checkpoint pathway** ensure?
* Each kinetochore is properly attached to spindle microtubules * Prevents separation of duplicated chromosomes until conditions are met ## Footnote This pathway is vital for maintaining genomic stability.
75
What is the **mitotic checkpoint complex** composed of?
* MAD2/MAD3 * BUB3 * Bub1 kinase * CDC20 ## Footnote These proteins are involved in the spindle assembly checkpoint.
76
What triggers the **exit from mitosis**?
Cdc14 protein phosphatase ## Footnote It activates APC/C and dephosphorylates mitotic CDK substrates.
77
What are the **two divisions** in meiosis?
* First division: homologous chromosomes pair and segregate * Second division: chromatids are separated ## Footnote This process results in haploid germ cells.
78
What occurs during **prophase I** of meiosis?
* Chromosomal condensation starts (leptotene) * Homologous chromosomes pair (zygotene) * Crossing-over occurs (pachytene) * Homologous chromosomes start moving apart (diplotene) ## Footnote These stages are critical for genetic recombination.
79
What is the role of **cohesins** during meiosis?
* Hold sister chromatids together * Link homologous chromosomes during metaphase I ## Footnote Cohesins are essential for maintaining chromosome structure during cell division.
80
What is the significance of **p53** in the cell cycle?
* Induces cell cycle arrest * Activates transcription of CKI p21 * Triggers apoptosis in severe DNA damage ## Footnote p53 is known as the 'Guardian of the Genome' and is frequently altered in cancers.
81
What are **proto-oncogenes**?
* Encode proteins that promote cell division * Can become oncogenes when mutated ## Footnote Defective proto-oncogenes contribute to cancer development.
82
What is the **function of ATR and ATM kinases**?
* ATR activates in response to DNA lesions * ATM activates in response to DNA strand breaks ## Footnote Both kinases play a role in the DNA damage response system.
83
What is the **result of meiosis**?
Four haploid daughter cells ## Footnote This process reduces the chromosome number by half.
84
True or false: **Meiosis II** is simpler than meiosis I.
TRUE ## Footnote Meiosis II closely resembles mitosis but results in haploid cells.
85
What is the **stage between the two divisions of meiosis** called?
Interkinesis ## Footnote Cells during this stage have a haploid number of chromosomes but a diploid amount of DNA.
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