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IB Biology 22-24 > Topic 7: DNA Replication, Transcription, Translation > Flashcards

Topic 7: DNA Replication, Transcription, Translation Flashcards

1
Q

Compare the genetic material of prokaryotes and eukaryotes. [6]

A

Prokaryotic DNA: Plasmids present, circular, one chromosome, naked DNA, no introns, found in nucleotide region

Eukaryotic DNA: No plasmids, linear, many chromosomes, has histones, introns and extrons, in the nucleus

Both: Use DNA as genetic material

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2
Q

Explain the process of DNA replication. [8]

A
  • Semi-conservative replication
  • Helicase unwinds the double helix
  • And separates strands by breaking hydrogen bonds
  • Each strand of parent DNA used as templates
  • DNA polymerase adds nucleotides
  • Synthesis from 5’ to 3’
  • Complementary base pairing
  • Adenine-Thymine, Cytosine-Guanine
  • Synthesis is continuous on the leading strand, non-continuous on the lagging strand
  • Okazaki fragments form on the lagging strand
  • DNA polymerase I replace RNA primer with DNA
  • DNA ligase joins Okazaki fragments
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3
Q

State the components of a nucleosome.

A

DNA and histone

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4
Q

State a chemical modification of a nucleosome to impact gene expression.

A

Methylation, acetylation, phosphorylation, epigenetic tags

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5
Q

Outline the structure and functions of nucleosomes. [4]

A
  • Found in eukaryotes
  • DNA wrapped around histones
  • Histones in a group of eight
  • Regulates transcription
  • Supercoils chromosomes
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6
Q

Identify enzymes used in DNA replication.

A

DNA polymerase, helicase, DNA ligase, RNA primase

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7
Q

Explain the role of Okazaki fragments in DNA replication. [3]

A
  • Formed by non-continuous synthesis on the lagging strand
  • Because replication must occur in the 5’ to 3’ direction
  • Replication starts repeatedly, moving away from the replication fork
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8
Q

Describe the relationship between genes, polypeptides, and enzymes. [4]

A
  • Genes are a sequence of DNA bases
  • Genes code for a specific sequence of amino acids
  • Enzymes are proteins composed of polypeptides
  • Sequence of amino acids determines tertiary structure
  • Enzymes involved in replication/transcription/synthesis of polypeptides
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9
Q

Distinguish between RNA and DNA. [3]

A

DNA

  • double stranded
  • deoxyribose
  • adenine, thymine, guanine, cytosine
  • all helical

RNA

  • single stranded
  • ribose
  • adenine, uracil, guanine, cytosine
  • three forms (mRNA, tRNA, rRNA)
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10
Q

Explain how translation is carried out, from the initiation stage onwards. [9]

A
  • Steps: Initiation, elongation, termination
  • mRNA binds to the small ribosomal unit of tRNA
  • Ribosome slides along mRNA to the start codon (AUG)
  • Triples of anticodons on tRNA bind to triples of codons on mRNA
  • Complementary base pairing
  • Adenine-Uracil, Cytosine-Guanine
  • Second tRNA enters A site and binds to codons
  • Peptide bond forms between the amino acids
  • Ribosome moves along mRNA in a 5’ to 3’ direction
  • tRNA that lost its amino acid detaches in the E site
  • Translation terminated when stop codon reached
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11
Q

Explain the methods and aims of DNA profiling. [8]

A
  • Obtain DNA sample
  • From hair or blood
  • DNA amplified through PCR
  • DNA cut into fragments
  • Using restriction enzymes
  • DNA fragments separated through gel electrophoresis
  • Using electrical fields
  • Separated by size
  • Forms pattern of bands unique to the individual
  • Used in crime scene investigation
  • Used in paternity testing
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12
Q

Explain the significant of complementary base pairing for replication, transcription, and translation. [8]

A
  • A-T, C-G in DNA
  • A-U, C-G in RNA
  • Replication: CBP ensure identical nucleotide sequence of new complementary strands
  • Semi-conservative replication
  • Transcription: CBP produces mRNA sequence complementary to DNA sequence
  • Translation: CBP converts mRNA sequence into specific amino acid sequence
  • tRNA carries triplets of bases - anticodons
  • mRNA carries triples of Nucleosomes - codons
  • Anticodons bind to complementary codons
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13
Q

Describe ribosome structure. [6]

A
  • Made of protein
  • Made of mRNA
  • Large subunit and small subunit
  • Three tRNA binding sites on large subunit
  • A site, P site, E exit
  • One mRNA binding site
  • 70s in prokaryotes, 80s in eukaryotes
  • Can be free or bound (rough ER)
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14
Q

Explain the process of transcription leading to mRNA formation. [8]

A
  • Unwinds double helix and separates strands
  • RNA polymerase binds to promoter on DNA
  • Nucleoside triphosphate
  • Binds to antisense strand of DNA
  • Synthesis in 5’ to 3’ direction
  • Using CBP A-U, C-G
  • Until terminator signal is reached
  • RNA detaches, DNA rewinds
  • RNA polymerase detaches from DNA
  • Introns removed from eukaryotes to form mature mRNA
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15
Q

State the bonds that i) Connect base pairs in a DNA molecule; ii) Link DNA nucleotides into a single strand.

A

I) Hydrogen bonds
Ii) Covalent bonds

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16
Q

Explain tRNA in translation. [3]

A
  • tRNA attaches to the amino acids
  • tRNA moves to the ribosome
  • Triplets of anticodons bind to triplets of codons on mRNA
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17
Q

Explain the roles of specific enzymes in prokaryotic replication. [7]

A
  • Helicase: Unwinds DNA double helix
  • And separates strands by breaking hydrogen bonds
  • DNA Primase: Adds primer to DNA
  • DNA Gyrase: Relieves strain on replication fork
  • DNA Polymerase III: Begins replication at primer
  • Synthesis in 5’ to 3’ direction
  • DNA Polymerase I: Replaces RNA with DNA
  • DNA Ligase: Links Okazaki fragments
  • DNA Polymerase I and III: Proofread for mistakes
18
Q

Outline how translation relies on complementary base pairing. [3]

A
  • Specific amino acids attached to specific tRNA
  • Anticodons on tRNA bind to codons on mRNA
  • A-U, C-G
  • Translation converts sequence of mRNA nucleotides to polypeptide chain
19
Q

Describe PCR including Taq DNA polymerase. [4]

A
  • Amplifies DNA
  • Cycles through high and low temperatures
  • Taq withstands high temperatures without denaturing
  • High temperatures break hydrogen bonds between DNA strands
  • Taq adds complementary bases
20
Q

Explain benefits and risks of GMO crops. [8]

A

Environmental benefits: Pest-resistant crops made, less insecticides, longer shelf life, shorter growing times

Environmental risks: Affects non-target organisms, monoculture lessens biodiversity, overuse of herbicides

Human health benefits: Increased nutritional value, produce toxin-free crops

Human health risks: Proteins from transferred genes could be toxic, GMO effects on human unclear

21
Q

Outline role of ribosomes in translation. [4]

A
  • Produces polypeptide from mRNA sequence
  • mRNA and tRNA bind to ribosome
  • tRNA base anticodons are complementary to mRNA codons
  • Amino acids bind by peptide bonds
  • Ribosome moves along the mRNA
22
Q

Describe the genetic code and its relationship to polypeptides and proteins. [5]

A
  • Genetic code: Triplets of nucleotides called codons
  • Bases: DNA - ATCG, RNA - AUCG
  • Each codon codes for a specific amino acid
  • DNA transcribed to mRNA via CBP
  • mRNA translated to polypeptide chain
  • Some codons are start or stop codons
  • Each gene codes for a polypeptide
23
Q

Outline a gene transfer technique. [5]

A
  • Plasmid removed from bacteria
  • Plasmid is a small circle of DNA
  • Restriction enzyme forms sticky ends
  • Restriction enzyme cuts DNA with desired gene
  • DNA added to open plasmid
  • DNA Ligase joins nicks
  • Recombinant DNA inserted into host cell
24
Q

Explain DNA replication. [3]

A
  • Semi-conservative replication
  • Helicase unwinds double helix
  • Separated strands are templates for new strands
  • Nucleotides join template strands through CBP
  • DNA polymerase joins nucleotides in new strands
25
Q

Compare prokaryotic and eukaryotic DNA.

A

Prokaryotic: In cytoplasm, has plasmid, circular

Eukaryotic: In nucleus, no plasmid, linear

Both: Double helix of bases ATCG

26
Q

Describe steps to process a small sample of DNA. [6]

A
  • Use PCR to amplify the DNA
  • Restriction enzymes cut DNA
  • Use gel electrophoresis to separate fragments in size
  • Creates DNA profiles
  • Make comparisons between patterns
  • DNA can be processed long after
27
Q

Explain how DNA base sequence is conserved during replication. [5]

A
  • Semi-conservative replication
  • Uses DNA polymerase
  • Helicase unwinds double helix and separates strands by breaking hydrogen bonds
  • Forms leading and lagging strand
  • DNA polymerase replicates template strands via CBP (A-T, C-G)
  • Replicates from 5’ to 3’ direction
  • Newly formed strand is identical to the other template strand
28
Q

The Hershey and Chase experiment supported DNA as the hereditary material. Describe the experiment. [3]

A
  • Radioactive isotopes used to label virus
  • Proteins labelled with radioactive sulfur, DNA labelled with radioactive phosphorus
  • Phage infects bacterium
  • Only viral DNA enters bacterium
  • Parts of phage remaining outside bacterial cell are removed
  • Bacteria contain the labelled DNA
29
Q

State one other function of DNA sequences that do not code for protein.

A
  • Regulate gene expression
  • Act as promoter
  • Introns
30
Q

Describe the Meselson-Stahl experiment.

A
  • Proved semi-conservative replication
  • Bacteria grown in broth containing N15 (heavy nitrogen isotope)
  • Sample was spun in a centrifuge, all heavy nitrogen settled at the bottom
  • N15 sample added to N14 (light nitrogen) broth
  • After one round of replication, DNA spun in a centrifuge again
  • DNA settled in the middle of the tube - mixture of both N15 and N14
31
Q

Outline the use of named enzymes in gene transfer using plasmids. [6]

A
  • plasmids removed from bacteria
  • restriction enzymes cut plasmids at target sequence
  • DNA fragments of other organism cut using same restriction enzyme
  • complementary sticky ends produced
  • DNA segment added to open plasmid
  • sealed using ligase
  • reverse transcriptase makes DNA copies of mRNA
  • recombinant plasmid inserted into host cell
  • cloned to produce new genes
32
Q

Explain the control of gene expression in eukaryotes. [8]

A
  • mRNA conveys genetic information from DNA to ribosomes
  • gene expression requires production of specific mRNA through transcription
  • most genes are turned off
  • some genes only expressed in certain cells
  • transcription factors increase/decrease transcription
  • hormones affect gene expression
  • nucleosomes limit access of transcription factors to DNA
  • DNA methylation/acetylation to control gene expression
  • introns contain positive/negative gene regulators
33
Q

Explain the consequences of altering a DNA base in the genome of an organism. [8]

A
  • altering a base in DNA is a point mutation
  • only has an effect if base is in a gene
  • when mRNA is produced by transcription one mRNA base is different
  • one codon in mRNA is different
  • one amino acid is different in the polypeptide
  • polypeptide produced by translation of mRNA
  • some base changes do not change the amino acid coded for
  • structure of polypeptide altered
  • usually polypeptide does not function as well
  • e.g. sickle cell anemia mutation from GAG to GTG
34
Q

Distinguish between transcription and translation. [4]

A
  • DNA is transcribed, mRNA is translated
  • transcription produces RNA, and translation produces protein
  • RNA polymerase is used only in transcription, ribosomes used only in translation
  • transcription in the nucleus of eukaryotes, translation in cytoplasm
  • tRNA needed for translation but not for transcription
  • sugar-phosphate bonds in transcription and peptide bonds in translation
35
Q

Describe the primary, secondary and tertiary structure of a polypeptide. [3]

A
  • Primary: sequence and number of amino acids
  • Secondary: formation of alpha helices and beta pleated sheets stabilized by hydrogen bonding
  • Tertiary: further folding stabilized by interactions between R groups
  • Quaternary: exists in protein with >1 polypeptide chain
36
Q

Outline the process of DNA profiling. [4]

A
  • sample of DNA obtained (hair/blood)
  • PCR used to amplify
  • using Taq DNA polymerase
  • tandem repeats amplified
  • gel electrophoresis to separate bands
  • according to length/size
  • pattern of bands unique to individual
  • e.g. forensics/paternity testing
37
Q

Outline the role of DNA polymerase III in DNA replication. [4]

A
  • binds to template strand at primer
  • adds nucleotide to template strand
  • using complimentary base pairing
  • links nucleotides with sugar-phosphate bonds
  • builds new strand in 5’ to 3’ direction
  • synthesis on lagging strand is discontinuous (Okazaki fragments)
38
Q

Explain how living organisms ensure that the amino acid linked to tRNA is always correct. [2]

A
  • enzymes ensure that a specific amino acid binds to tRNA
  • tRNA activating enzyme
  • enzyme only binds to this tRNA
  • different activating enzymes for different tRNAs
  • attached amino acid corresponds to anticodon
39
Q

During translation, three binding sites for tRNA molecules are used. Outline how each of the binding sites is used. [3]

A
  • binding sites on the ribosome
  • A: binding of an tRNA carrying an amino acid
  • P: where amino acid links to polypeptide via peptide bond
  • E: exit/detachment of tRNA from ribosome
40
Q

Outline how proteins can be separated by gel electrophoresis. [3]

A
  • separates molecules based on size and charge
  • proteins differ in size/charge
  • placed in a block of gel
  • gel placed in an electrical field, an electric current is ran through
  • proteins move through gel
  • separated according to size, small proteins move further
  • size markers/ladders used

IB Biology 22-24 (13 decks)

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