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0 - Biology > DNA & Gene Expression > Flashcards

DNA & Gene Expression Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

Give four adaptations of DNA.

A
  1. Very stable - doesn’t change
  2. Double helix & backbone - protect bases from damage
  3. Weak H-bonds - strands are easily separated
  4. Very large - carries lots of information
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2
Q

What are the two experiments for proving DNA is hereditary material?

A
  1. Pneumonia in mice experiment
  2. Virus in bacteria with radioactively labelling using sulphur/phosphorus
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3
Q

State the components of a DNA nucleotide.

A
  1. Deoxyribose
  2. Phosphate group
  3. Organic base
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4
Q

What are the four DNA bases?

A
  1. Adenine
  2. Cytosine
  3. Guanine
  4. Thymine
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5
Q

What are the base pairs?
How many H-bonds are there between the bases in each pair?

A
  • Adenine & Thymine - 2 bonds
  • Cytosine & Guanine - 3 bonds
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6
Q

Which bases are:

  1. Single ring
  2. Double ring
A
  1. Cytosine & Thymine
  2. Adenine & Guanine
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7
Q

What are genes?

A

Sections of DNA that code for a specific polypeptide.

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8
Q

What are alleles?

A

Different forms of a gene.

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9
Q

What are the names of the:

  1. Coding sections of a gene
  2. Non-coding sections of a gene
A
  1. Exons
  2. Introns
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10
Q

What is the structure of a chromosome?

A

A single chromatid (before the DNA is replicated)

OR

Two chromatids joined at a centromere (after DNA replication)

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11
Q

What holds the DNA in place in a chromosome?

A

Histone proteins

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12
Q

What solution is used to find out the densities of DNA relative to each other?

A

Caesium chloride (CsCl)

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13
Q

Why DNA replication is semi-conservative?

A
  • Each strand acts a template
  • Each new helix contains one “new” strand and one “parental” strand
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14
Q

What process ensures exact DNA replication?

A

Complementary base pairing

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15
Q

What is the role of DNA helicase?

A

Breaks the H-bonds and separates the two strands

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16
Q

What is the role of DNA polymerase?

A

Joins the activated nucleotides together, forming the second polynucleotide strand

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17
Q

What are the steps of DNA hybridisation?

A
  • Extract & purify DNA from two species
  • Cut DNA into short pieces
  • Label the DNA of one species
  • Mix the DNA and heat
  • All DNA to cool (reanneal)
  • Separate hybrid DNA
  • Heat gently
  • Measure the temperature at which the strands separate
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18
Q

What is a codon?

A

A base triplet on mRNA which codes for an amino acid

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19
Q

What is meant by the degenerative code of DNA?

A

An amino acid can be coded for by more than one triplet

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20
Q

What are the stages of protein synthesis?

A
  1. Transcription
  2. Splicing
  3. Translation
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21
Q

What happens during transcription?

A

Occurs in the nucleus

  1. DNA helicase separates the two strands (breaks H-bonds)
  2. Free RNA nuceotides bind to the template strand by complementary base pairing
  3. RNA polymerase joins the free nucleotides
    • Forms phosphodiester bonds
  4. When a terminator region is reached, transcription ends
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22
Q

What happens during splicing?

A

Spliceosomes splice out (remove) the introns from the pre-mRNA to form mature mRNA

23
Q

What happens during translation?

A

Occurs at the ribosome

  1. Amino acid carried to mRNA by tRNA
    • Each tRNA carries a specific amino acid
  2. The anticodon is attracted to its complementary codon on the mRNA
  3. The amino acids are joined by a peptide bond
  4. The tRNA detaches and collects another amino acid
  5. The ribosome moves along the mRNA
  6. Continues until a stop codon is reached
24
Q

What is a mutation? What are the types?

A

A change in the DNA base sequence resulting from:

  • Substitution of a base
  • Deletion of a base
25
Q

What can happen when a base is substituted?

A
  1. Nonsense: results in a stop codon
  2. Mis-sense: results in a different amino acid
  3. Silent: results in no change in the amino acid sequence
26
Q

What happens when a base is deleted?

A

Results in a frame-shift which affects all the amino acids after the deletion

27
Q

What is a mutagenic agent? What are some examples?

A

Anything which increases the frequency at which mutations occur. For example:

  1. High energy radiation (X-ray, UV, gamma rays)
  2. High energy particles
  3. Tobacco tar
  4. Nitrous acid
  5. Benzene
28
Q

What genes regulate cell division?

A

Proto-oncogenes: stimulate cell division

Tumour suppressor gene: slow (inhibit) cell division

29
Q

What happens when the genes regulating cell division mutate?

A

Proto-oncogenes:

  • The pathway is activated without the relevant signalling molecule

Tumour-suppressor genes:

  • The gene becomes inactivated so cell division isn’t inhibited
30
Q

What differs between specialised cells?

A

The genes which are expressed

31
Q

What is a stem cell?

A

Unspecialised cells which can differentiate into other specialised cells

32
Q

What are the types of stem cell?

A
  • Totipotent: can develop into any cell (embryonic stem cells)
  • Multipotent: can develop into some cells (adult stem cells)
33
Q

What are meristem cells?

A

Totipotent stem cells found in plants

Found where the plant is growing (shoots/roots)

They can be used to grow a whole plant in vitro

34
Q

How is gene expression regulated by oestrogen?

A
  1. Oestrogen diffuses across phospholipid bilayer into cell
  2. Binds to a transcription factor causing an inhibitor to be released: binding site exposed
  3. This allows the transcription factor to bind the specific sequence of bases on the DNA
  4. This initiates transcription of mRNA (the gene is expressed)
35
Q

What is siRNA?

A

Small interfering RNA: short, double stranded pieces of RNA

36
Q

How is gene expression regulated by siRNA?

A
  • One strand binds to an enzyme
  • The strand then binds to the complementary bases on the mRNA
  • The enzyme breaks up the mRNA into small pieces
  • Hence, the protein isn’t produced (gene isn’t expressed)
37
Q

How can DNA fragments be made?

A

Reverse transcriptase

Restriction enzymes

38
Q

What is reverse transcriptase? How does it work?

A
  • Viral enzyme, catalyses “reverse transcription”
  • mRNA is used as a template to produce cDNA (complementary DNA)
  • Produces a copy of a gene without introns
39
Q

What to restrictin enzymes do?

A

Cut DNA at specific recognition sites

Forms sticky ends

40
Q

What are the types gene cloning?

A

In vitro - in test tubes

In vivo - in living cells

41
Q

How are genes cloned in vitro?

A

Done by PCR (polymerase chain reaction):

  1. DNA sample mixed with:
    • DNA polymerase
    • Free nucleotides (dNTPs)
    • Primers
  2. Sample heated to 95ºC
    • Separate strands
  3. Cool to 55ºC
    • Allow primers to anneal
  4. Heat to 72ºC
    • Allow DNA polymerase to work
42
Q

How are genes cloned in vivo?

A

Done by transforming bacteria:

  1. DNA and plasmid cut with the same restriction enzyme
    • To produce same sticky ends
  2. Mixed with DNA ligase which joins the two pieces of DNA
  3. Plasmids introduced into bacteria by shock treatment
  4. Identification 1 - bacteria with a plasmid
    • Ampicillin resistance gene
  5. Identification 2 - bacteria with plasmid with the gene
    • Tetracylin resistance gene or GFP
  6. Desired bacteria grown in vats at optimal conditions
  7. Protein/gene/DNA fragment is extracted and purified
43
Q

What is gene therapy? What are types?

A

Using cloned genes to treat genetic diseases. Types:

  1. Somatic - inserted into body cells
  2. Germ line - inserted into sex cells
44
Q

What vectors are used to insert a gene into a cell?

A

Viruses

Liposomes

45
Q

What is the cause of the symptoms of cystic fibrosis?

A
  1. Caused by deletion three bases in the CFTR gene
    • Results in non-functional Cl- channel
  2. Cl- ions cannot leave cells
    • Water does not follow by osmosis
  3. Leads to thick and sticky mucus
46
Q

How can cystic fibrosis be treated?

A

Normal CFTR gene inserted into a virus/liposome

Administered by a nasal spray

47
Q

What are DNA probes?

A

Short strands of DNA that can be used to identify specific base sequences

Radioactively/fluorescently labelled

48
Q

How can DNA be sequenced?

A

Sanger method

Restriction mapping

49
Q

What is the Sanger method for determining the DNA base sequence?

A
  1. In a test tube:
    • DNA strand
    • DNA polymerase
    • Primers
    • Free nucleotides
    • Modified nucleotides (ddNTPs) one of A*, C*, G* or T*
  2. The modified nucleotides cause DNA replication to terminate
  3. The four tubes are run on an electrophoresis gel, the bands are read from the furthest nucleotide first to determine the base sequence
50
Q

How can the base sequence be determined using restriction mapping?

A
  1. DNA is digested using restriction enzymes
  2. Fragments are separated by gel electrophoresis
  3. Done with multiple enzymes to determine the order of the fragments
51
Q

What does gel electropheresis do? How does it work?

A

Separates DNA fragements by size

  1. The DNA is digested with restriction enzymes
  2. The fragments are placed in wells of an agarose gels
  3. A current is passed through the gel
    • The smallest fragments move the furthest
  4. The fragments are compared to fragments of known size
52
Q

How does genetic fingerprinting work?

A

Uses STRs/minisatellites - found in everyone’s DNA

Inherited from parents and unique to a person

53
Q

What is the process of genetic fingerprinting?

A
  1. Extract DNA and purify
  2. Digest with restriction enzymes
  3. Separate by gel electrophoresis
  4. Heat to separate strands
  5. Transfer to a nylon membrane
  6. Add fluorescent/radioactive probes
  7. Autoradiography - expose x-ray film (if using radioactive)
54
Q

What are the uses of genetic fingerprinting

A

Paternity testing

CSI

0 - Biology (13 decks)

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