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Bio 111 > Chapter 15: Genes and Proteins > Flashcards

Chapter 15: Genes and Proteins Flashcards

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Biology 101 flashcards
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
Q

Transcription in eukaryotes: Initation

A

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

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26
Q

Transcription in Eukaryotes: Elongation

A

The FACT complex (facilitates chromatin transcription) removes and reassembles the nucleosomes as polymerase synthesizes the mRNA

27
Q

Transcription in Eukaryotes: Termination

A

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
Q

What is post-transcriptional processing in eukaryotes?

A

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
Q

What are the specific ways enzymes modify pre-mRNA before translation?

A

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
Q

What is pre-mRNA splicing?

A

It involves the precise removal of introns from the primary RNA transcript

31
Q

What catalyzes the splicing process?

A

Protein complexes that are called spliceosomes, composed of protein and RNA molecules called snRNA

32
Q

Where do spliceosomes recognize sequences?

A

At the 5’ and 3’ end of the intron

33
Q

What is alternative splicing?

A

the presence of introns allows for alternative RNA splicing
Protein domains can correspond to specific exons

34
Q

Transcription in prokaryotes

A

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

  • 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
Q

Transcription in Prokaryotes: Initation

A

It involves promoter, transcription factors, RNA polymerase

36
Q

What is a promoter?

A

Promoter is a piece of DNA sequence upstream that indicates where the RNA polymerase should bind and start

37
Q

What are transcription factors?

A

Proteins that aid in the initation and regulation of transcription

38
Q

What are RNA polymerases?

A

Proteins that synthesizes the RNA transcript (Only adding nucleotides onto the 3’ of the growing RNA)

39
Q

Transcription in prokaryotes: Elongation

A

RNA polymerase adds complimentary nucleotides (A, U, C, G) to make the
mRNA

  • 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
Q

Transcription in prokaryotes: Termination

A

It is also called Rho dependent termination- which is when a rho protein travels along mRNA and interacts with RNA polymerase terminating transcription

Rho Independent termination- formation of mRNA hair pin when GC rich region (inverted bases) reached, then followed by A rich residues, terminates transcription

41
Q

What are the types of eukaryotic polymerases?

A

RNA polymerase I, RNA polymerase II, RNA polymerase III

42
Q

What does RNA polymerase I do?

A

transcribes rRNA genes

43
Q

What does RNA polymerase II do?

A

transcribes protein-coding genes

44
Q

What does RNA polymerase III do?

A

transcribes rRNA, tRNA, and smaller nuclear RNA genes

45
Q

Translation

A

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
Q

What are the molecular components of Translation?

A
  1. Transfer RNAs
  2. Ribosome
  3. messenger RNA
  4. polypeptide
47
Q

molecular component- tRNA

A
  • 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
Q

molecular components- ribosomes

A
  • 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
Q

Translation Process: Initation

A

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
Q

Translation Process: Elongation

A

a) tRNAs move in with the appropriate amino acid, the
amino acid chain grows using peptidyl transferase

51
Q

Translation Process: Termination

A

a) Stop codon is reached
b) The amino acid chain then is processed

52
Q

What are the three stop codons?

A

UAG,UGA,UAA

53
Q

After translation polypeptides/proteins may undergo?

A

Modifcations via the endomembrane system
This affects their 3 dimensional shape, and it occurs in the endoplasmic reticulum

Ribosomes can be bound to the ER and produce the polypeptide into the ER.

54
Q

What is a mutation?

A

A mutation is a change in the genetic material of the cell

typically referring to a change in the sequence of nitrogenous bases

55
Q

What are the different classes of mutations?

A

Point mutations, frameshift mutations, and chromosomal mutations

56
Q

Point Mutations

What is a substituation point mutation?

A

The replacement of 1 base pair with another

57
Q

Point Mutation

What are the different types of substitutions

A
  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
Q

Point Mutations

What is an insertion point mutation?

A

The additionof 1 base pair within the genome

59
Q

What is a deletion point mutation?

A

The removal of 1 base pair-within the genome

60
Q

What is a frameshift mutation?

A

These are changes in nucleotide base pairs within the genome that causes a reading frame shift

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
Q

What are the 2 ways frameshift mutations occur?

A

Insertions- adds new nucleotides in the genome
Deletions- removes nucleotides from the genome

62
Q

What are mutagens?

A

Mutagens are physical or chemical agents that can cause mutations

ƒ Like radiation, X-rays, UV
ƒ Arsenic, nitrosamine, nitrogen mustards (Bendamustine & Altretamine)
ƒ Think about carcinogens!

63
Q

When do spontaneous mutations occur?

A

They can occur during DNA replication, recombination, or repair

Bio 111 (4 decks)

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