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IB Biology SL > TEST 7 - DNA & PROTEIN SYNTHESIS > Flashcards

TEST 7 - DNA & PROTEIN SYNTHESIS Flashcards

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1
Q

Nucleic Acids

A

Polymers made of nucleotides. Each nucleotide consists of:
- A 5-carbon sugar (deoxyribose in DNA, ribose in RNA)
- A phosphate group (forms the backbone)
- A nitrogenous base (A, T, C, G in DNA; A, U, C, G in RNA).
Nucleic acids store and transmit genetic information.

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2
Q

DNA (Deoxyribonucleic Acid)

A

A double-stranded nucleic acid with these features:
- Sugar: Deoxyribose (lacks an oxygen atom compared to ribose).
- Bases: Adenine (A), Thymine (T), Cytosine (C), Guanine (G).
- Structure: Double helix, antiparallel strands (one 5’ to 3’, the other 3’ to 5’).
- Function: Contains genetic information needed for the development and functioning of living organisms.
- Exam Tip: Be ready to sketch and label a DNA molecule.

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3
Q

RNA (Ribonucleic Acid)

A
  • Sugar: Ribose.
  • Bases: Adenine (A), Uracil (U), Cytosine (C), Guanine (G).
  • Function: Plays roles in protein synthesis (mRNA, tRNA, rRNA).
  • Exam Tip: Know how RNA differs structurally and functionally from DNA.
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4
Q

Complementary Base Pairing

A

A mechanism of hydrogen bonding between nitrogenous bases:
- Adenine (A) pairs with Thymine (T) in DNA (2 hydrogen bonds).
- Cytosine (C) pairs with Guanine (G) in DNA and RNA (3 hydrogen bonds).
- In RNA, Adenine (A) pairs with Uracil (U) instead of Thymine (T).

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5
Q

Nucleotide

A

The monomer unit of nucleic acids.
- Composed of a pentose sugar, phosphate group, and nitrogenous base.
- Linked by phosphodiester bonds to form a polynucleotide chain.
Exam Tip: Know how to identify and label the components of a nucleotide in a diagram.

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6
Q

Purines

A

Double-ring nitrogenous bases:
- Adenine (A) and Guanine (G).
- Found in both DNA and RNA.

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7
Q

Pyrimidines

A

Single-ring nitrogenous bases:
- Cytosine (C), Thymine (T) (in DNA), and Uracil (U) (in RNA).
- Found in DNA (C, T) and RNA (C, U).

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8
Q

Phosphodiester Bonds

A

Covalent bonds that link nucleotides in a polynucleotide strand:
- Formed between the phosphate group of one nucleotide and the 3’ carbon of the sugar in the next nucleotide.
- Create the sugar-phosphate backbone of DNA and RNA.

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9
Q

Chromosome

A

A structure made of coiled DNA and proteins (histones):
- Contains many genes.
- Visible during cell division.
- Humans have 46 chromosomes (23 pairs) in somatic cells.

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10
Q

Gene

A

A sequence of nucleotides in DNA that codes for a specific protein:
- Consists of coding regions (exons) and non-coding regions (introns).
- Determines the amino acid sequence of a polypeptide.

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11
Q

DNA Replication

A

The process of producing an identical copy of DNA:
- Occurs in the S phase of interphase.
- Key enzymes:
> Helicase: Unwinds the double helix.
> DNA polymerase: Adds nucleotides to the new strand in the 5’ to 3’ direction.
> Ligase: Joins Okazaki fragments on the lagging strand.
- Semi-conservative: Each new DNA molecule consists of one old strand and one new strand.

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12
Q

Genome

A

The complete set of genetic material in an organism:
- Includes all chromosomes and mitochondrial DNA.
- Human genome: Approximately 3 billion base pairs.

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13
Q

Hydrogen Bonds in DNA

A

Weak bonds between complementary bases:
- Stabilize the DNA double helix.
- Allow for easy separation during replication and transcription.

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13
Q

Semi-Conservative Replication

A

A mechanism where each daughter DNA molecule retains one original strand:
- Demonstrated by the Meselson-Stahl experiment.
- Ensures genetic consistency across cell divisions.

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14
Q

Okazaki Fragments

A

Short DNA segments synthesized on the lagging strand during replication:
- Joined together by DNA ligase.
Result from the antiparallel nature of DNA.

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14
Q

DNA Replication Overview

A

The process of DNA replication involves:
- Step 1: Enzymes (like helicase) attach to DNA and break hydrogen bonds between base pairs.
- Step 2: The double helix unwinds, creating replication forks.
- Step 3: DNA polymerase synthesizes new complementary strands.
- Directionality: Leading strand is synthesized continuously toward the replication fork; the lagging strand is synthesized in fragments (Okazaki fragments) away from the fork.

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15
Q

Tissue Replacement and Repair

A

DNA replication is essential for replacing cells in tissues that have been lost or damaged (e.g., during wound healing). New cells require an identical copy of DNA to function properly.

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16
Q

DNA Polymerase

A

The enzyme that:
- Joins nucleotides to form new DNA strands.
- Ensures proper base pairing and assembles nucleotides in the correct order.

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17
Q

Helicase

A

An enzyme responsible for unwinding and separating the DNA strands to allow replication enzymes to access the DNA.

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18
Q

Semi-Conservative Replication

A

A replication mechanism where:
- Each daughter DNA molecule contains one original strand and one newly synthesized strand.
- Proven by the Meselson-Stahl Experiment, which used nitrogen isotopes (¹⁵N and ¹⁴N) to demonstrate the semi-conservative model.

19
Q

Meselson-Stahl Experiment

A

A landmark experiment that demonstrated DNA replication is semi-conservative.
- Key Steps:
> Bacteria were grown in heavy nitrogen (¹⁵N) and then transferred to light nitrogen (¹⁴N).
> DNA samples were centrifuged to analyze density.
> Results showed intermediate and light bands, supporting the semi-conservative model.

20
Q

PCR (Polymerase Chain Reaction)

A

A laboratory technique used to amplify small amounts of DNA.
- Steps:
> Denaturation: DNA strands are separated by heating (~95°C).
> Annealing: Primers bind to target sequences (~55°C).
> Elongation: DNA polymerase (e.g., Taq polymerase) synthesizes new DNA strands (~72°C).
- Applications: Crime scene investigations, paternity testing, and disease diagnostics.

21
Q

Taq Polymerase

A

A heat-resistant enzyme from Thermus aquaticus, used in PCR to synthesize DNA at high temperatures without denaturing.

22
Q

Gel Electrophoresis

A

A technique to separate DNA fragments by size.
- DNA is loaded into a gel, and an electric field is applied.
- Smaller fragments move faster and farther through the gel.
- Used in DNA profiling and genetic analysis.

23
Q

Applications of PCR and Gel Electrophoresis

A

Combined, these techniques are used for:
- Crime investigations.
- Paternity testing.
- Identifying genetic disorders.
- Testing for viruses (e.g., coronavirus).

24
Q

STRs and VNTRs

A
  • STRs (Short Tandem Repeats): Short DNA sequences (2–6 base pairs) repeated many times.
  • VNTRs (Variable Number Tandem Repeats): Longer DNA sequences (hundreds of base pairs) repeated fewer times.
  • Used to create unique DNA fingerprints for individuals.
25
Q

Making a DNA Profile

A
  • DNA is extracted, amplified (via PCR), and cut into fragments.
  • Fragments are separated using gel electrophoresis to create a unique DNA pattern.
  • Applications include forensic analysis and ancestry tracing.
26
Q

DNA Ladder

A

A marker applied in the first lane of a gel electrophoresis gel to estimate the sizes of DNA fragments in unknown samples.
Purpose: Allows accurate comparison of fragment lengths.

27
Q

Crime Scene Investigations

A
  • Process: DNA profiles from a crime scene are compared with those of suspects or victims.
  • Key Indicator: Matching DNA bands suggest a high likelihood that samples belong to the same person.
  • Significance: Provides strong evidence for identifying suspects.
28
Q

Paternity Investigations

A
  • Process: DNA from the mother, child, and suspected father is compared.
  • Key Indicator: Bands that match between the child and the suspected father, but not the mother, indicate paternity.
  • Applications: Establishes biological relationships in legal and personal contexts.
29
Q

Practice Question: Identifying Smallest DNA Fragment

A
  • Example Task: Given a gel electrophoresis image, identify the smallest fragment by locating the band that traveled the farthest.
  • Tip: Smaller fragments migrate faster and appear farther from the wells.
30
Q

Practice Question: Identifying Paternity

A
  • Example Task: Analyze gel electrophoresis bands to determine which suspected father matches the child’s DNA, accounting for maternal contributions.
  • Key Skill: Match unique bands between the child and father that are not present in the mother’s DNA profile.
31
Q

Interpreting DNA Profiles in Crime and Paternity Cases

A
  • For crime investigations, matching all bands between the suspect and evidence indicates guilt.
  • For paternity tests, shared bands between the child and suspected father confirm biological relations.
32
Q

Three Classes of RNA

A
  • mRNA (Messenger RNA):
    Carries the genetic code from DNA to ribosomes.
    Contains codons that specify amino acids.
  • rRNA (Ribosomal RNA):
    Structural component of ribosomes, essential for protein synthesis.
  • tRNA (Transfer RNA):
    Transfers amino acids to ribosomes.
    Contains an anticodon complementary to mRNA codons.
33
Q

Gene Expression

A

The process of using genetic information to produce proteins.
Two Steps:
- Transcription: DNA is copied into mRNA.
- Translation: mRNA is used to assemble amino acids into a protein.

34
Q

Transcription

A

The synthesis of RNA from a DNA template.
- Key Enzyme: RNA polymerase.
- Steps:
> RNA polymerase binds to the promoter region of DNA.
> DNA helix unwinds, exposing bases for pairing.
> RNA nucleotides are assembled complementary to the DNA template strand.
> mRNA is formed and exits the nucleus through nuclear pores.

35
Q

Hydrogen Bonding and Complementary Base Pairing in Transcription

A
  • Maintains stability of the DNA helix.
  • Enables accurate pairing of RNA nucleotides to the DNA template strand during transcription.
36
Q

Stability of DNA Templates

A
  • Ensured by the sugar-phosphate backbone and hydrogen bonds between nucleotides.
  • Protects genetic information from damage and mutations caused by external factors (e.g., UV radiation, chemicals).
37
Q

Transfer RNA (tRNA)

A

A molecule that transports amino acids to ribosomes.
- Structure:
> Contains an anticodon region for mRNA recognition.
> Carries a specific amino acid at the opposite end.
- Function: Ensures correct amino acids are added to the growing polypeptide chain.

38
Q

Steps of Translation

A
  • Initiation: Ribosome assembles at the start codon on mRNA.
  • Elongation: Amino acids are added to the growing chain via peptide bonds.
  • Termination: The ribosome reaches a stop codon, and the completed protein is released.
39
Q

Prokaryotic vs. Eukaryotic Gene Expression

A
  • Prokaryotes:
    > Transcription and translation occur simultaneously in the cytoplasm.
  • Eukaryotes:
    > Transcription occurs in the nucleus.
    > mRNA undergoes processing (splicing, capping, polyadenylation) before translation in the cytoplasm.
40
Q

Translation Overview

A
  • Location: Ribosomes in the cytoplasm.
  • Initiation: AUG start codon recognized by tRNA carrying methionine.
  • Process: tRNA anticodons pair with mRNA codons; amino acids form peptide bonds.
  • Stop Codons: UAA, UAG, UGA signal termination.
41
Q

Steps in Translation

A

Step 1: Small ribosomal subunit binds to mRNA at the start codon (AUG).
Step 2: tRNA carrying methionine pairs with the start codon in the P-site.
Step 3: Large ribosomal subunit joins, forming the initiation complex.
Step 4: Elongation continues as ribosome moves, transferring the polypeptide to new tRNA in the A-site.
Step 5: Peptide bonds form between amino acids; tRNA in E-site exits.
Step 6: Translation ends at a stop codon, releasing the completed polypeptide.

42
Q

Genetic Code

A
  • Definition: Set of rules by which information in mRNA codons translates into amino acids.
  • There are 64 different nRNA codons, 61 code for specific Amino Acids
  • Features:
    > Degenerate: Multiple codons can specify the same amino acid (e.g., GGU, GGC, GGA = Glycine).
    > Universal: Same genetic code across most organisms.
  • Start Codon: AUG (Methionine).
  • Stop Codons: UAA, UAG, UGA.
43
Q

mRNA Codon Table

A
  • Function: Deciphers which amino acids correspond to mRNA codons.
  • Example Codons:
    > AUG = Methionine (start).
    > UUU = Phenylalanine.
    > UGA = Stop.
44
Q

Comparing Transcription and Translation

A
  • Transcription:
    Template: DNA.
    Location: Nucleus.
    Product: mRNA.
    Energy Source: RNA polymerase activity.
  • Translation:
    Template: mRNA.
    Location: Ribosome (cytoplasm).
    Product: Polypeptide chain.
    Energy Source: ATP for tRNA charging.
45
Q

Mutations in Protein Structure

A
  • Point Mutations:
    > Silent: No effect on amino acid.
    > Nonsense: Introduces a stop codon, truncating the protein.
    > Missense: Substitutes one amino acid for another.
  • Example:
    > Normal: GAA → Glutamic acid.
    > Mutated: GUA → Valine (missense).
46
Q

Sickle Cell Anemia

A
  • Cause: Point mutation in the β-globin gene (GAG → GTG).
  • Effect:
    > Alters hemoglobin structure.
    > Changes red blood cell shape to “sickle.”
    > Reduces oxygen transport efficiency.
  • Symptoms: Fatigue, anemia, pain due to blocked blood vessels.
47
Q

Consequences of Sickle Cell Mutation

A
  • Primary Structure: Altered amino acid sequence.
  • Quaternary Structure: Deforms hemoglobin.
  • Red Blood Cell Shape: From biconcave disc to rigid sickle.
  • Result: Decreased cell flexibility, clumping in blood vessels.

IB Biology SL (10 decks)

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