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Biology-12 > DNA Unit Test > Flashcards

DNA Unit Test Flashcards

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1
Q

What does DNA stand for?

A

Deoxyribonucleic acid

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2
Q

Who was credited for the discovery of the structure of DNA?

A

Francis Crick and James Watson (largely work of Rosalind Franklin)

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3
Q

What did Rosalind Franklin use to discover what DNA was made of?

A

X-Ray photograph of DNA crystal

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4
Q

What are the basic units that are make up DNA?

A

Nucleotides (phosphate group, nitrogenous base and the carbon sugar (deoxyribose)

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5
Q

What are the 4 different nitrogenous bases?

A

Adenine, Guanine, Thymine and Cytosine

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6
Q

What are purines?

A

Double ringed structures; adenine and guanine

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7
Q

What are pyrimidines?

A

Single ringed structures; thymine and cytosine

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8
Q

What is Chargaffs Rule?

A

Thymine pairs with adenine

Cytosine pairs with guanine

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9
Q

What holds together DNA?

A

Held by hydrogen bonds

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10
Q

How many hydrogen bonds is between A-T

A

2 (less complex bc count letters)

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11
Q

How many hydrogen bonds is between cytosine and guanine?

A

3 hydrogen bonds

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12
Q

What does 5’ to 3’ mean?

A

Fifth carbon in deoxyribose point upward in one strand and downward in the other

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12
Q

What does 5’ to 3’ mean?

A

Fifth carbon in deoxyribose point upward in one strand and downward in the other

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13
Q

How many base pairs are in DNA approx?

A

6 billion base pairs long

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14
Q

How does DNA fit the massive info in each cell?

A

DNA is coiled upon itself to form chromosomes

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15
Q

How does DNA coil upon itself?

A

Histones (+ charged proteins) act as “spools” on which DNA molecule coils

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16
Q

What is a chromatin fibre?

A

Nucleosomes coil upon themselves

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17
Q

How does DNA replicate?

A

Free-floating nucleotides in nucleus are assembled into a copy of parental DNA

18
Q

What are the 2 models of DNA replication?

A
  • conservative replication
  • semi-conservative replication
19
Q

What is conservative replication?

A
  • one daughter DNA molecule is constructed entirely from free floating nucleotides
  • parental DNA molecule remains unchanged (conserved)
20
Q

What is semi-conservative replication?

A
  • each daughter dna molecule has one strand of parental nucleotides and one stand made from free-floating nucleotides
  • half the parental material is conserved in each daughter DNA molecule (semi-conserved)
21
Q

How did they prove semi-conservative?

A

Matthew Meselson and Franklin Stahl performed an experiment
- they used cultures of e. Coli that we’re given nutrients containing either “heavy” nitrogen 15N or a more common isotope 14N

22
Q

What are the steps of the Meselson-Stahl Experiment?

A
  1. Grow e.coli in presence of 15N only (parental)
  2. Take parental bacteria and allow then to reproduce in presence of 14N (gen 1)
    3 Take gen 1 bacteria and allow them to reproduce in presence of 14N only (gen 2)

Shows that DNA is semi conservative takes half from parent and half from free floating nucleotides

23
Q

What is the correct version of DNA replication?

A

Semi conservative

24
Q

What needs to happen before DNA replication?

A

-b4 it can occur highly coiled and condensed DNA molecule must be “straightened” into linear sequence of nucleotides
- enzymes serve this function

25
Q

Go over DNA replication

A

Look at test or notes

26
Q

What way does DNA build?

A

5’ to 3’

27
Q

What is the central dogma of genetics?

A

DNA stored genetic code necessary for synthesizing all the different proteins in our body

28
Q

What are genes?

A

Each protein coded for by specific segment of DNA (coded info)

29
Q

Where is DNA found and where does it go?

A

DNA is found in nucleus and proteins are constructed by ribosomes in cytoplasm

30
Q

How do instructions get from nucleus to ribosomes?

A

Make mRNA which moves out of nucleus into cytoplasm to make copies

31
Q

What is the code of DNA made into

A

mRNA (messenger RNA)
- Ribosomes can translate the code into a protein
- mRNA moves into cytoplasm (takes the code) and delivers it to meet ribosome

32
Q

What 2 steps does protein synthesis occur in?

A
  • Transcription
  • Translation
33
Q

How do you read DNA?

A

3’ to 5’ build from 5’ to 3’

34
Q

What 3 steps does transcription occur in?

A

Step 1: Initiation
- begins “upstream” of gene, at a promoter region

Step 2:
Elongation
- DNA is unwound, exposing template strand at beginning of gene
- RNA polymerase synthesizes mRNA molecule in 5’ to 3’ direction, through complimentary base pairing with DNA template

Step 3:
- RNA polymerase reaches end of gene and encounters termination sequence
- RNA synthesis stops
- mRNA and RNA polymerase

35
Q

What is a promoter?

A

Is a specific sequence of DNA nucleotide that RNA polymerase can recognize and bind to

36
Q

What is post-transcriptional modification?

A

mRNA is modified in 3 ways before it leaves the nucleus
1. 5’ cap (seven methyl guanosine ribonucleotide is added to 5’ end of mRNA- helped mRNA attach to the ribosome during translation) and helps to protect

  1. Poly-A-Tail: string of about 50-259 adenine ribonucleotides are added to 3’ end of mRNA- protects the mRNA from RNA digesting enzymes in the cytoplasm
  2. Introns are removed: mRNA strand made of sections that code for specific protein (exons) and those that don’t (introns)

Proteins called spliceosomes “cut out” introns, leaving on ur one

37
Q

What are spliceosomes?

A

Proteins that count out introns as they are not important

38
Q

How many and what types of RNA does translation require?

A

mRNA: copy of instructions for constructing a specific protein

tRNA: delivers individual amino acids to ribosome for construction of protein

rRNA: ribosomes consist of 2 subunits: each is a combo of rRNA and protein

39
Q

What is the structure of tRNA?

A
  • single stranded and double stranded sections
  • unique anticodon
    Anticodon: 3 nucleotide segment that corresponds to codon on mRNA
  • Carries a specific amino acid
40
Q

Do all codons make amino acids?

A

No, 61/64 codons specify an amino acid
3 are stop codons

41
Q

What is the wobble hypothesis?

A

Pairing of the anticodon with first two nucleotides of the codon is always precise, but there is flexibility in pairing with the third nucleotide of the codon

42
Q

What are the 3 steps of Translation?

A

Step 1: Initiation
- tRNA with anticodon that corresponds to AUG brings met and forms a complex with small ribosomal subunit
- complex binds to 5’ end of mRNA and scans along until it reaches AUG start codon
- Large ribosomal subunit binds to complete ribosomes

Step 2: Elongation
- Ribosomes move along mRNA reading codons
- tRNA continues to deleiver amino acids to ribosome
- Peptide bonds form between amino acids
- Empty tRNA released
- Polypeptide chain folds into specific 3D shape

Step 3: Termination
- Occurs when a stop codon is read by a ribosome
- Ribosomal subunits seperate, tRNA and polypeptide chain released

Biology-12 (8 decks)

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