Chapter 5: smth for cell biology

WHat type of bond is there between Adenine and thymine? What abt cystine and guanine?

a double bond, a triple bond

How are monomers condensed together?

Through phosphdiester bonding, which is a type of bond where a phosphate group connects a 3’ carbon to the 5’ carbon of another monomer

How is chromosome painting performed?

By using nucleotide sequences to hybridize a specific chromosome, allowing for the chromosome to be viewed under a fluorescence microscope

What is translocation?

A type of chromosome mutation that occurs when one part of a chromosome joins another, causing certain genes to be expressed more than other ones

Why are human genomes huge?

Due to there being a huge amount of noncoding genes in between coding genes in DNA

What can happen to chromosomes during evolution?

they can be rearranged, causing species to have bigger chromosomes than others

What is the active gene expression stage?

A stage that allows the cell to respond to the environment around them

What are the 3 elements needed for DNA to be copied?

• Centromere

• telomeres

• origin of replication

What is the origin of replication?

A region where DNA replication begins, with eukaryotes containing multiple regions that stop and initiate replication simultaneously. allowing for DNA to be copied faster

What occurs during the M-phase after DNA is replicated?

chromatin are condensed into large chromosome structures that are visible in a microscope

How are nucleosomes formed?

When linear DNA wraps around 8 copies of histone proteins, forming the bead like structure that can be condensed further into radial loop domains

How long is the DNA that wraps around histone proteins?

147 nucleotide pairs long

Why are some broken down DNA samples resistant to digestion?

Due to them being wrapped around histones, preventing enzymes from accessing them

What are the 4 kinds of histones?

• H2A

• H2B

• H3

• H4

What a majority of histones amino acids fold into?

A majority of them fold into a globular structure in the middle of the nucleus with their N-terminus serving to organize the chromosome structure and gene expression

What is histone H1?

A type of histone protein that packages chromosomes at a higher level and can determine how dense the nucleosome is

How are nucleosomes folded further?

into radial loop domains by an SMC complex or cohesion

How does the SMC ring complex form nucleosomes into radial loop domains?

A hinge attached to the upper DNA region hydrolyzes ATP, causing the complex to open its "grip” from DNA and move away, stretching DNA into a larger loop

What are clam proteins?

Proteins that dictate the size and content of each chromosomal loop based on its own spacing and location

How are radial loop domains formed by cohesion?

Cohesion begins to a form large chromosome domain region with 2 clamp proteins coming together slowly and lock the loop once they completely come together

What is cohesin?

A type of SMC ring complex that organizes the structure of interphase chromosomes

What packages chromosomes during mitosis?

Condensin II and I

How does HETEROCHROMATIN undergo packing during mitosis?

cohesin is removed and condesin II begins to form large loops, with condesin I forming smaller loops inside the larger loops, packaging heterchromatin into a chromosome

What is one way that gene expression is regulated?

through the use of the chromatin remodeling complex

What is the chromatin remodeling complex?

A protein that hydrolyzes ATP in order to rotate the DNA wrapped around in the nucleosome, allowing for some of the DNA sequence to either be exposed or buried

• Promoting the binding of proteins to the DNA or preventing the binding of proteins to the DNA

What do the 4 different histones make up?

they make up the core of a histone

What is sticks out from each of the 4 kinds of histone?

Each of them have their own N terminal region that sicks out of the histone called histone tails that provides gene expression regulation

How can each histone be modified?

Multiple positions in their amino acids that can be modified through chromatin modification that adds either an acetyl group, methyl group, or phosphate group to the position

What are euchromatin?

Chromosome regions that are less densely packaged with there being two kinds: active euchromatin and quiescent euchromatin

What are heterochromatin?

Chromatin that are more densely packaged

What is Active euchromatin

A type of euchromatin that contains genes that are expressed

What is quiescent euchromatin?

A type of euchromatin that contains genes that remain silenced until they are needed, which causes the euchromatin to become a facultative heterochromatin that expresses the gene and returns to its inactive state once done

What are constitutive heterochromatin?

These are regions in a chromosome that remain in a heterochromatin state and are permanently condensed

• With an example of these being centromeres and telomeres

How do heterochromatin specific histone modifications help form heterochromatin and allow them to spread?

The modified histone recruits a “reader-writer” protein complex that contains a histone-modifying enzyme, allowing for the modified histone to be identified by the reader and spread onto neighboring nucleosome by the writer while recruiting heterochromatin specific proteins in the process until it reaches a barrier DNA sequence, preventing the spread from continuing and reaching euchromatin regions

What does females having 2 X chromosomes potentially lead to?

It can potentially lead to high expression levels of every gene on both X chromosomes, which can result in problems occurring

What is determined at the early developmental stages of embryonic development?

One of the female X chromosomes are randomly turned into a barr body and remain condensed, with each cell division having that same chromosome remain condensed in every descendant of the original cell

What is the barr body?

the inactivated X chromosome of a female that is completely condensed and not expressed

What can occurs if a mom or dad has any mutations on their X chromosome that can lead to diseases?

50% of the cell will be able to carry out enough function in order to survive but is not always guaranteed

What is an example of X-inactivation?

Tortoiseshell cats as they are always females with one of their X chromosomes being inactive and carrying the orange fur gene while the other X chromosome is active and carries the black fur gene

How is heterochromatin inherited?

During DNA replication, the histone modification of the parent is passed done to the daughter strands and once replication is complete, the reader-writer complex begins to spread the modification to neighboring nucleosomes along with heterochromatin specific proteins binding to the modified histones, reassembling the same chromatin structure found in the parent in order to retain the identity of the parent cell