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Cell Biology > Module 3: The Nucleus > Flashcards

Module 3: The Nucleus Flashcards

(37 cards)

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1
Q

The Nucleus

A

Control center of the cells → contains DNA, RNA, and protein

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2
Q

DNA (basic definition)

A

A long unbranched and linear polymer containing the genetic info of an organism
A large amount is stored in the cell

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3
Q

Coding regions of the cellular genome

A

The parts of DNA that actually code for the different proteins and RNAs needed for cell function and growth

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4
Q

Storage of DNA

A

Efficient, space-saving packaging of DNA via histones = proteins that help pack DNA into nucleosomes
Nucleosides gather together → pack DNA tighter = chromosomes

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5
Q

Chromosomes

A

Most tightly packed form of DNA
Contain euchromatin and heterochromatin

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6
Q

Euchromatin

A

Loose, transcriptionally active DNA

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7
Q

Heterochromatin

A

Tight, transcriptionally inactive DNA

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8
Q

Histones

A

DNA binding proteins → structural proteins
When associating with DNA = chromatin
5 histone proteins: H2A, H2B, H3, H4 and H1

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9
Q

H2A, 2B, 3 and 4 histone proteins

A

Form the “core” of the nucleosome → allowing the DNA to wrap around it and package tightly

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10
Q

“Beads-on-a-string” structure of DNA aka the 11nm structure

A

Created by nucleosomes

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11
Q

Condensation of nucleosomes into chromosomes

A

Nucleosomes = beads on a string aka 11nm structure → condenses into the 30nm chromatin structure → condenses further into the 300nm fiber → further condenses into final structure of the chromosome

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12
Q

H1 histone protein

A

Keeps the stray DNA that comes off the nucleosome attached so it stays condensed and tightly packed
Like a “hair clip”

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13
Q

Histone’s 2nd role

A

Take part in gene regulation and expression

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14
Q

Chemical structure of histones

A

Contain positively charged amino acids (like arginine and lysine) that can interact with the negative charge of DNA

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15
Q

How does the chemical structure of histones help them play a role in DNA organization?

A

The positively charged amino acids in histones interact with the negative charge of DNA → these charges are what help to hold the DNA onto the nucleosome → have an important role in binding

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16
Q

How does the chemical structure of histones help them play a role in gene regulation and expression?

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A

The positive charge of histones are involved in how proteins like histone acetylases and histone deacetylases act directly on histone proteins to affect gene expressionand regulation

17
Q

Histone acetylases

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A

Activate gene expression by acetylating histone proteins → removes the positive charge of the histone = DNA is able to be much more loosely associated with histone proteins → open tointeracting with DNA replication proteins

18
Q

Histone deacetylases

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A

Do the opposite of histone acetylases → remove the acetyl groups from histone proteins = the # of positive charges on the histones increase → strengthens the interaction between DNA and histone protein = DNA unable to be expressed/ regulated

19
Q

DNA vs. RNA: structure

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A

DNA = double stranded; has thymine as one of its 4 nitrogenous bases
RNA = single-stranded; has uracil base in the place of thymine

20
Q

How are both DNA and RNA necessary for the cell’s overall function?

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A

DNA carries the genetic info and RNA acts as the “messenger”/ “coder” for different protein products produced by genes

21
Q

Process of transcription and translation

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A

DNA is first transcribed to RNA → RNA is translated into proteins with the help of ribosomes
This process needs many different proteins in order to occur correctly (without error)
Bottom line: RNA = a messenger of genetic info → so the info can be converted into protein

22
Q

RNA transcription in prokaryotes

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A

Much simpler → only 1 type of RNA polymerase that care of all types of RNA synthesis
1. RNA polymerase will recognize a promoter sequence →2. the binding site for the RNA polymerase
3. This starts the synthesis of RNA in the 5’ -3’ direction → DNA = a template strand
4. Process stops once prokaryotic RNA polymerase reaches the termination signal
5. Prokaryotic RNA polymerase will dissociate from the DNA → 6. The newly synthesized RNA is released

23
Q

RNA transcription in eukaryotes

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A

More complex → uses 3 types of RNA polymerases. each serving a different function → the main one used in RNA synthesis = RNA polymerase II
Also uses different transcription factors due to the coding and non-coding regions of DNA, where not all of DNA is translated into protein
Specifically these regions are introns (non-coding) and exons (coding)

24
Q

Steps of eukaryotic RNA transcription

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A
  1. RNA polymerase II transcribes all of the DNA, creating an immature mRNA → contains both introns and exons
  2. An RNA splicing complex will remove the introns, creating the mature mRNA → contains only exons. This process is splicing.
  3. A 5’-cap and a 3’-poly-A tail are added to either end of the mature mRNA molecule → protects it from being digested by enzymes in the cytoplasm
  4. The mRNA exits the nucleus, going into the cytoplasm →ready for translation into proteins using ribosomes.
25
Importance of splicing in eukaryotic RNA transcription
Allows the all to make many different proteins using different combos of exons, from the same RNA transcript
26
Mnemonic regarding introns and exons
Introns stay inside the nucleus, while exons exit the nucleus to be translated
27
Promoter sequence and termination signal
Both are specific sequences of nitrogenous bases located in the DNA Promoter sequence = what RNA polymerase recognizes to bind to and start transcription Termination signal = tells the RNA polymerase to end transcription and dissociate from the DNA
28
Gene expression
Differences in gene expression give cells specialized functions within the cell → allows for many different types of cell that don't all produce the same proteins All cells have the same DNA but parts of the DNA being expressed differently by each cell produces specific functions
29
How are different cell types able to synthesize different types of proteins from the same DNA?
The expression of genes within the genome has to be altered from cell to cell, allowing for different cell types to synthesize different protein types. This is achieved via many different mechanisms: transcriptional control via DNA methylation, histone acetylation/deaceytylation, processing control via RNA splicing, translational control, and mRNA degradation control
30
Bacteria's unique method of gene expression regulations
Uses operons, which are made of sets of genes that code for different structural proteins The proteins are transcribed in series only under certain conditions Example: the lac operon in E. coli
31
The lac operon and its control elements
A strip of gelnes found in the bacteria E. coli Includes the inducer gene, the promoter region, the operator binding site, and the structural genes (located downstream) The genes are only transcribed in the presence of lactose When there is no lactose → the repressor protein binds to the operator → RNA polymerase can't start transcription
32
Negative regulation
A repressor protein binds to the operator when an operon's conditions are not met → so when RNA polymerase binds to the promoter site, it cannot pass the repressor and transcribe the structural genes of the operon This type of regulation keeps genes from being transcribed at times that the cell doesn't need them
33
Positive regulation
When an activator protein is used to increase the transcription of genes
34
Control of gene expression in eukaryotes
Can be controlled by loosening or tightening chromatin structure Histone acetylases will decrease the interaction between the DNA and histone proteins → allows the DNA to be transcribed and creating a looser chromatin structure (euchromatin) Histone deacetylases will increase the interaction between DNA and histone proteins → decreases the likelihood of DNA transcription and creating a tighter chromatin structure (heterochromatin)
35
Cell memory
Each new generation of cells of one type keeps the same genes active and inactive respectively Can be caused by the inheritance of different gene regulatory components, DNA methylation, or by the inheritance of heterochromatin and enchromatin Example: the inheritance of an inactive X chromosome (Barr body) in females
36
Inheritance of gene regulatory components
Inherited as they are multi-protein complexes that remain bound to DNA during replication → results in the inheritance of the regulatory state of that protein complex
37
DNA methylation
One of the only gene regulation mechanism that account for cell memory CpG islands within the DNA are methylated and thereby inactivated CpG (C=cytosine, p= phosphate, G= guanine) These methylation patterns can then be inherited through DNA replication

Cell Biology (10 decks)

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