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bio 12 exam > molecular genetics > Flashcards

molecular genetics Flashcards

1
Q

nucleotides consist of

3

A

Nucleotides consist of 3 parts:
- 5 carbon sugar: deoxyribose
- Phosphate group: attached to #5 carbon by an ester bond
- Nitrogen Base: attached to the #1 carbon by a glycosyl bond

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2
Q

complimentary base pairing

4

A
  • 2 strands are joined together by Hydrogen bonds between the base pairs of each strand
  • This pairing is complementary – A pairs with T and G pairs with C
  • A purine must always pair with a pyrimidine which results in a constant diameter
  • Bonding does not occur between A and C or G and T because of lack of hydrogen bonding which would create instability
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3
Q

step 1 DNA replication

A

study paper

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4
Q

step 2 DNA replication

A

study paper

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5
Q

step 3 DNA replication

A

study paper

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6
Q

central dogma of molecular genetics

A

DNA is TRANSCRIBED into complementary messenger RNA, and ribosomes TRANSLATE messenger RNA into a specific sequence of amino acids, which are used to build proteins

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7
Q

steps involved in transcription and translation using the genetic code

A

study paper

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8
Q

transcription

2

A

Transcription is the process where DNA is copied into RNA:
- This occurs in the nucleus.
- It is divided into 3 sequential processes: initiation, elongation, and termination

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9
Q

initiation

4

A
  • Enzyme RNA polymerase binds to the DNA and unwinds near the beginning of a gene
  • This occurs in both prokaryotes and eukaryotes
  • Promoter: is the nucleotide sequence that lies just upstream from the start of a gene, it allows for the binding of RNA polymerase
  • The promoter has a section with a high percentage of adenine and thymine bases – called the TATA box
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10
Q

elongation

5

A
  • RNA polymerase begins to build the single stranded RNA molecule it can do so without a primer
  • RNA is made in the 5’ 3’ direction using the 3’5’ DNA strand called the template strand
  • The other DNA strand is referred to as the coding strand as it contains the same sequence as the new RNA molecule
  • As RNA polymerase passes along the template strand, a temporary DNA/RNA double helix will form
  • Once RNA polymerase starts transcription another RNA polymerase may start transcribing if there is room at the promoter
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11
Q

termination

4

A
  • Transcription of a gene is terminated when the RNA polymerase recognizes a termination sequence: a particular sequence of bases (3 codons)
  • RNA transcript is released & RNA polymerase is free to bind to another promoter region
  • Another termination mechanism: termination sequence is a string of adenines, which is transcribed into uracil
  • Nuclear proteins bind to poly uracil site and stop transcription
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12
Q

post-transcriptional modifications

2

A
  • The transcribed RNA is a precursor to mRNA and is vulnerable to conditions outside of the cell nucleus (premRNA)
  • It must undergo additional modifications for protection before it can exit
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13
Q

poly- a tail

2

A
  • Poly-A polymerase adds a chain of 50-250 adenine nucleotides to the 3’ end of the pre-mRNA
  • Allows it to be translated efficiently and protects it from attacks by RNA digesting enzymes in cytosol
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14
Q

5’ cap

2

A
  • A sequence of 7 methylated guanines are added to the start of the pre-mRNA
  • It functions as the initial attachment site that the ribosome recognizes and will use
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15
Q

exons

A

sequence of DNA/RNA that codes for a gene

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16
Q

introns

4

A
  • a non-coding sequence of DNA/RNA
  • Introns are interspersed and if they were left in mRNA they would alter the sequence of amino acids used to build the protein
  • Introns must be deleted from eukaryotes in order to make the correct protein later on
  • Prokaryotes do not contain any introns
17
Q

spliceosome/ mRNA splicing

A
  • enzyme-protein complex that removes introns from mRNA and joins exons
  • The removal of introns is signaled by small ribonucleic proteins (snRNPs)
  • They bind to an intron by recognizing the boundary sequences – this causes the intron to loop outs
  • This brings the 2 exons close together now we have an active spliceosome
  • Spliceosome excises the introns and splices the exons together
18
Q

alternative splicing

2

A
  • Process that produces different mRNA’s from pre-mRNA allowing more than one possible
    polypeptide to be made from a single gene
  • Exons are joined in different combinations creating a family of related proteins with various combinations of amino acids.
19
Q

codons

A

Each triplet of RNA bases = 1 codon which gets translated into amino acids.

61 of the codons specify 20 different amino acids.

20
Q

wobble hypothesis

A
  • the 3rd base in a codon can change, but it still codes for the same amino acid.
  • This is called redundancy or wobble hypothesis, and is important in minimizing errors which could lead to mutations.
21
Q

start codons

A

initiator codon
AUG (=methionine)

22
Q

stop codons

A
  • UAA, UAG, UGA.
  • These are called stop codons and they signal the end of a polypeptide chain.
  • This causes the ribosome to terminate translation.
23
Q

lac operon

A
  • The lac operon is a cluster of genes that contain the DNA sequences to regulate the protein needed for the metabolism of lactose (energy source for prokaryotes)
  • When no lactose is present, the production of those proteins is blocked in order to conserve energy.
  • The lac operon is known as an inducible operon because the inducer (signal molecule e.g., lactose) inactivates the repressor and allows the gene to be transcribed and translated to produce a protein.
24
Q

trp operon

A
  • Tryptophan is an important amino acid that is used to build proteins.
  • Many prokaryotes can synthesize tryptophan independently, but they can also take it up from the environment.
  • The trp operon is found in prokaryotic cells only. It regulates the production of tryptophan.
  • The trp operon is an example of enzyme repression: the operon is repressed (turned off) when high levels of tryptophan are present. Therefore no tryptophan will be produced.
25
Q

substitution

A

missense- amino acid is exchanged for another
nonsense- codon is replaced by stop codon
silent- does not change the amino acid

26
Q

insertion

A

frameshift- causes the reading frame of codons to change

27
Q

deletion

A

frameshift- causes the reading frame of codons to change

28
Q

inversion

A

missense- amino acid is exchanged for another

bio 12 exam (8 decks)

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