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Bio 111 > Chapter 15: Genes and Proteins > Flashcards

Chapter 15: Genes and Proteins Flashcards

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1
Q

What is a gene?

A

A specific sequence of nucelotides on a strand of DNA

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2
Q

Genes usually lead to the production of what?

A

a specific protein product or an RNA molecule
- this can/will lead to the development of a specific trait (ex. blood type)

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3
Q

How did scientists find this out about genes?

A

One gene-one enzyme hypothesis (1941)

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4
Q

What is one gene-one enzyme?

A

Hypothesized, by Beadle and Tatum, that each gene encodes for a single enzyme

based on this, they surmised that each gene would influence a specific step in a metabolic pathway

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5
Q

Beadle and Tatum Experiment (1941)

A

They worked on mutants of bread mold, discovered genes provide the instructions for making proteins

groundbreaking but also an oversimplifcation of what actually happens with genes and protein synthesis

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6
Q

Do genes encode for proteins other than enzymes?

A

yes, many proteins exist and are needed that are not enzymes

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7
Q

Genes only encode whole proteins?

A

False, some genes can encode a subunit of a protein

Many proteins are composed of multiple different polypeptides, a different gene encodes for each one of those polypeptides

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8
Q

Do genes make non-coding RNAs?

A

YES, (rRNA, tRNA, siRNA, miRNA, snRNA,
etc.)

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9
Q

What is the process of alternative splicing

A

Many genes have more than one coding regions (exons) and can be arranged in varying ways which will result in the development of different proteins

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10
Q

Flow of Genetic Information

A

DNA -> RNA -> Protein
(The Central Dogma of Molecular Biology)

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11
Q

What is gene expression?

A

When DNA directs protein synthesis

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12
Q

What are the two major processes, that express genes?

A

Transcription and Translation

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13
Q

What is Transcription

A
  • Synthesis of RNA under the direction of DNA
  • Produces messenger RNA (mRNA)
  • produces the template for translation
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14
Q

What is Translation

A
  • The synthesis of a polypeptide under the direction of an mRNA
  • Occurs on ribsomes
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15
Q

Where is genetic information stored?

A

In the sequence of nucleotides

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16
Q

What are codons?

A

Nucleotides in an mRNA sequence code for amino acids in 3 nucleotide portions (triplets)

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17
Q

how do you know it’s triplets?

A

There are 20 amino acids (“aa”) and 4 nucleotides (“nt”), (A, C, G, T/U)
* Therefore, we need at least 20 different ‘codes’ to read

1 nucleotide codon= 4 different codes
2 nucleotide codon= 16 different codes
3 nucelotide codon= 64 different codes

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18
Q

How many possible codons code for the 20 amino acids?

A

64

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19
Q

Because there is many codons to code for each amino acid, what does this support?

A
  • Multiple codons can code for the same amino acid, or one amino acid can have more than one codon make it

There is 3 stop codons and 1 start codon

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20
Q

What does the reading frame refer to?

A

Which nucleotide starts the first codon

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21
Q

For each segment of DNA, how many possible reading frames can there be?

A

6

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22
Q

What does a reading frame always start with?

A

It always starts with the start codon (AUG)

this codes for the AA Methionine

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23
Q

Evolution of the Genetic Code

(Background info)

A
  • The genetic code is nearly universal
  • All organisms use DNA, which means they all use the same nt (A, C, G, T…or U in place of T when looking at RNA)
  • There is exceptions to this rule, but it also means that almost all organisms use the same set of AA to build their many different proteins

  • Provides important evidence for the common origin of life on Earth
  • Suggests life likely evolved from an ancestral organism in which the same code was used
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24
Q

Transcription in eukaryotes

A

It occurs in the nucleus, and have additional intervening step - RNA processing where pre-mRNA is processed into functionally active mRNA

The steps are
1. Initiation
2. Elongation
3. Termination

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25
Transcription in eukaryotes: Initation
It involves a promoter, transcription factors, and RNA polymerase Transcription factors recognize the promoter RNA polymerase II then binds and forms the transcription initation complex
26
Transcription in Eukaryotes: Elongation
The FACT complex (facilitates chromatin transcription) removes and reassembles the nucleosomes as polymerase synthesizes the mRNA
27
Transcription in Eukaryotes: Termination
Different for each different polymerase * RNA polymerase II transcribes 1,000 – 2,000 nucleotides excess of the gene template which are removed during mRNA processing. * RNA polymerase I requires a termination protein that recognizes a specific 18 nucleotide sequence. * RNA polymerase III terminates transcription via hairpin formation. * After termination, the RNA needs additional processing...
28
What is post-transcriptional processing in eukaryotes?
Eukaryotic cells must modify RNA after transcription and before translation, so enzymes in the nucleus modify pre-mRNA before the genetic messages are dispatched to the cytoplasm
29
What are the specific ways enzymes modify pre-mRNA before translation?
a) Addition of a 5’ methylguanosine cap and b) Addition of a 3’ poly-A tail c) Intron splicing – removal of the non-coding introns.
30
What is pre-mRNA splicing?
It involves the precise removal of introns from the primary RNA transcript
31
What catalyzes the splicing process?
Protein complexes that are called spliceosomes, composed of protein and RNA molecules called snRNA
32
Where do spliceosomes recognize sequences?
At the 5' and 3' end of the intron
33
What is alternative splicing?
the presence of introns allows for alternative RNA splicing Protein domains can correspond to specific exons
34
Transcription in prokaryotes
There is no nucleus, so transcription occurs in the cytoplasm which is that same place as translation transcription/translation can be coupled in prokaryotes Newly made protein can quickly diffuse to its site of function The steps are: 1. Initation 2. Elongation 3. Termination ## Footnote * Prokaryotes do not require RNA transcript modification, which means RNA transcripts can be translated immediately after being transcribed * Because of these 2 points, a Prokaryote’s RNA transcript can be translated as transcription is progressing. * Multiple polymerases can transcribe a single gene * Numerous ribosomes can concurrently translate the mRNA transcripts into polypeptides. * This can allow a specific transcript and/or a specific protein to rapidly reach high concentrations in a cell
35
Transcription in Prokaryotes: Initation
It involves promoter, transcription factors, RNA polymerase
36
What is a promoter?
Promoter is a piece of DNA sequence upstream that indicates where the RNA polymerase should bind and start
37
What are transcription factors?
Proteins that aid in the initation and regulation of transcription
38
What are RNA polymerases?
Proteins that synthesizes the RNA transcript (Only adding nucleotides onto the 3’ of the growing RNA)
39
Transcription in prokaryotes: Elongation
RNA polymerase adds complimentary nucleotides (A, U, C, G) to make the mRNA ## Footnote * During elongation, the prokaryotic RNA polymerase tracks along the DNA template. * Then it synthesizes mRNA in the 5' to 3' direction, and unwinds and rewinds the DNA as it is read. * Elongation occurs at a rate of 40 nucleotides per second.
40
Transcription in prokaryotes: Termination
It is also called Rho dependent termination- which is when a rho protein travels along mRNA and interacts with RNA polymerase terminating transcription ## Footnote Rho Independent termination- formation of mRNA hair pin when GC rich region (inverted bases) reached, then followed by A rich residues, terminates transcription
41
What are the types of eukaryotic polymerases?
RNA polymerase I, RNA polymerase II, RNA polymerase III
42
What does RNA polymerase I do?
transcribes rRNA genes
43
What does RNA polymerase II do?
transcribes protein-coding genes
44
What does RNA polymerase III do?
transcribes rRNA, tRNA, and smaller nuclear RNA genes
45
Translation
Translation decodes mRNA * Polypeptides are formed when the amino group of one amino acid forms an amide bond with the carboxyl group of another amino acid * The reaction is catalyzed by ribosomes The steps are: 1. Initation 2. Elongation 3. Termination
46
What are the molecular components of Translation?
1. Transfer RNAs 2. Ribosome 3. messenger RNA 4. polypeptide
47
molecular component- tRNA
* tRNA molecules are not all identical, however they all: * Carry a specific amino acid on 1 end. * Have an anticodon on the other end. * Single RNA strand that is about 80 nucleotides long. * Utilize a specific Aminoacyl-tRNA synthetase to attach its amino acid
48
molecular components- ribosomes
* Protein and rRNA complex that facilitates the reading of mRNA and production of the corresponding polypeptide * Achieved through the paring of mRNA codons with tRNA anticodons. * Consists of 2 ribosomal subunits (these vary between prokaryotes and eukaryotes) * Has 3 binding sites for tRNA
49
Translation Process: Initation
a) mRNA attaches to the smaller subunit of the ribosome b) AUG is the start codon – a tRNA with the appropriate anticodon attaches c) The larger subunit of the ribosome then comes in
50
Translation Process: Elongation
a) tRNAs move in with the appropriate amino acid, the amino acid chain grows using peptidyl transferase
51
Translation Process: Termination
a) Stop codon is reached b) The amino acid chain then is processed
52
What are the three stop codons?
UAG,UGA,UAA
53
After translation polypeptides/proteins may undergo?
Modifcations via the endomembrane system This affects their 3 dimensional shape, and it occurs in the endoplasmic reticulum ## Footnote Ribosomes can be bound to the ER and produce the polypeptide into the ER.
54
What is a mutation?
A mutation is a change in the genetic material of the cell ## Footnote typically referring to a change in the sequence of nitrogenous bases
55
What are the different classes of mutations?
Point mutations, frameshift mutations, and chromosomal mutations
56
# Point Mutations What is a substituation point mutation?
The replacement of 1 base pair with another
57
# Point Mutation What are the different types of substitutions
1. Silent (Synonymous) * The single base pair change does not cause an amino acid change in the polypeptide. 2. Missense (Nonsynonymous) * The single base pair change causes an amino acid change in the polypeptide. * Can be very detrimental or not noticed at all. 3. Nonsense * The single base pair change causes a change from an amino acid to a stop codon. * Usually very detrimental!
58
# Point Mutations What is an insertion point mutation?
The additionof 1 base pair within the genome
59
What is a deletion point mutation?
The removal of 1 base pair-within the genome
60
What is a frameshift mutation?
These are changes in nucleotide base pairs within the genome that causes a reading frame shift ## Footnote The deletion of two nucleotides shifts the reading frame of an mRNA and changes the entire protein message, creating a nonfunctional protein or terminating protein synthesis altogether.
61
What are the 2 ways frameshift mutations occur?
Insertions- adds new nucleotides in the genome Deletions- removes nucleotides from the genome
62
What are mutagens?
Mutagens are physical or chemical agents that can cause mutations ## Footnote ƒ Like radiation, X-rays, UV ƒ Arsenic, nitrosamine, nitrogen mustards (Bendamustine & Altretamine) ƒ Think about carcinogens!
63
When do spontaneous mutations occur?
They can occur during DNA replication, recombination, or repair

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