the nucleus Flashcards
what does the nucleus contain
DNA
RNA
protein
define DNA
long unbranched and linear polymer that contains the genetic information of an organism
define coding regions
regions in the cellular genome of DNA that codes for the different proteins and RNAs necessary for cell function and growth
what are histones?
proteins that help package the DNA into nucleosomes
what are chromosomes?
most tightly packed form of DNA
euchromatin vs heterochromatin
euchromatin: loose, transcriptionally active DNA
heterochromatin: tight, transcriptionally inactive DNA
what is chromatin?
when DNA associates with histones
what are the 5 histone proteins?
H2A
H2B
H3
H4
H1
which histone proteins are the core of the nucleosome and what do they allow for?
H2A, 2B, 3
allows DNA to wrap around it and package it tightly
what gives DNA the beads on a string structure or 11nm structure?
nucelosomes
When the beads on a string structure of DNA condenses further, what does this create? what does it create when it condenses even further?
30nm chromatin structure
300nm fiber
what is the purpose of H1?
“hair-clip”
keeps the stray DNA that comes off the nucleosome attached so that it can stay condensed and tightly packed
how do histones play a role in gene regulation and expression?
- contain positively charged amino acids, such as arginine and lysine which can interact with the negative charge of DNA.
- These charges are in general what help to hold the DNA onto the nucleosome, and they play an important role in binding
what proteins act directly on histone proteins to affect gene expression and regulation?
histone acetylases
histone deacetylases
what do histone acetylases do?
activate gene expression by acetylating histone proteins
What is the purpose of histone acetylases activating gene expression by acetylating histone proteins?
removes the positive charge, and as a result, allows the DNA to be much more loosely associated with histone proteins, making it open to interacting with DNA replication proteins
what do histone deacetylases do?
remove acetyl groups from histone proteins, causing the amount of positive charges on the histones to increase, and thereby making the interaction between DNA and histone protein stronger, preventing the DNA from being expressed/regulated
DNA vs RNA
DNA
- double stranded
- thymine
- carries genetic information
RNA
- single stranded
- uracil
- messenger or coder for the different protein products that are produced by genes
(transcribed vs translated) DNA is first _______ to RNA and then RNA is ________ into proteins with the help of ribosomes
transcribed
translated
why does RNA act as a messenger of genetic information?
so the information can be converted into protein
what is the promoter sequence in RNA of prokaryotes?
a specific sequence of nitrogenous bases located within the DNA, where RNA polymerase will first recognize it
the promoter sequence of RNA in prokaryotes is the binding site for the RNA polymerase, which then starts the synthesis of RNA in the ____’ direction, using the DNA as a template strand
5’-3’
When does the process of RNA synthesis in the 5’-3’ direction stop (prokaryotes)?
once prokaryotic RNA polymerase reaches the termination signal, another sequence of nitrogenous bases within the DNA
Once prokaryotic RNA polymerase reaches the termination signal, what happens to it?
dissociate from the DNA and release the newly synthesized RNA
which is the main RNA polymerase used in eukaryotes?
RNA polymerase II
introns vs exons
introns: non-coding region
exons: coding region
what does RNA polymerase II do?
transcribe all of the DNA to create an immature mRNA, which contains both introns and exons
what does RNA splicing complex do?
removes introns to create mature mRNA which only contains exons
what is the mnemonic to remember which component is removed and which component stays in the mature RNA?
introns stay inside the nucleus, while exons exit the nucleus to be translated
what does splicing allow for?
can allow the cell to make many different proteins using different combinations of exons, from the same RNA transcript
After the mature mRNA is produced from splicing, a _____ and a _________ are added to either end of the molecule to protect it from being digested by enzymes in the cytoplasm.
5’ -cap
3’ -poly-A tail
Once the mRNA exits the nucleus and goes into the _________, it can be ________ into proteins using _______
cytoplasm
translated
ribosomes
why do we have many different cells that don’t produce the same proteins?
gene expression
what does gene expression do?
confer upon the cells specialized functions
what are the mechanisms that allow for gene expression to alter the cell to fulfill their function?
transcriptional control via DNA methylation, histone acetylation/deacetylation, processing control through RNA splicing, translational control, and mRNA degradation control
how does bacteria regulate gene expression?
operons
what are operons made of?
set of genes that code for differential structural proteins
what are lac operons?
- This is a strip of genes that are found in the organism E.Coli
- includes the inducer gene, the promoter region, the operator binding site, and the structural genes, which are located downstream
genes transcribed via operons are only transcribed in the presence of what?
lactose
what happens when no lactose is present with genes transcribed via operons?
the repressor protein binds to the operator
- even when RNA polymerase binds to the promoter site, it will not be able to pass the repressor and transcribe the structural genes
what is negative regulation?
prevents the genes from being transcribed at times when the cell does not need them
when does positive regulation occur?
when an activator protein is used to increase the transcription of genes
in eukaryotes, how can gene expression be controlled?
loosening or tightening chromatin structure
Histone acetylases will decrease the interaction between the DNA and histone proteins, what does this allow for?
allows the DNA to be transcribed and creating a looser chromatin structure (euchromatin)
Histone deacetylases will increase the interaction between DNA and histone proteins, what does this do?
decreases the likelihood of DNA transcription and creating a tighter chromatin structure (heterochromatin)
what is an example of inheritance by different gene regulatory components, DNA methylation, or by inheritance of heterochromatin and euchromatin?
inactive X chromosome (Barr body) in females
what is one of the only gene regulation methods that account for cell memory?
DNA methylation
how does DNA methylation work?
CpG (C=cytosine, p=phosphate, G=guanine) islands within the DNA are methylated and thereby inactivated
how can methylation patterns be inherited?
through DNA replication.
how can inheritance of the regulatory state of the protein complex occur?
gene regulatory components are inherited as they are multi-protein complexes that remain bound to DNA during replication
