Nucleic acids

🧬 NUCLEIC ACIDS – STUDY NOTES

1.1 Structure of DNA and RNA

πŸ”Ή Nucleotide (basic unit)

A nucleotide has 3 parts:

  • Phosphate group (circle)

  • Sugar (pentagon)

  • Nitrogenous base (rectangle)

πŸ‘‰ You can draw it like:

[Phosphate] β€” [Sugar] β€” [Base]

Β Β  (β—‹) Β  Β  Β  Β  (⬟) Β  Β  Β  (β–­)

πŸ”Ή DNA Structure

  • Double helix (twisted ladder)

  • Made of 2 strands

  • Sugar = deoxyribose

  • Bases:

    • Adenine (A)

    • Thymine (T)

    • Cytosine (C)

    • Guanine (G)

πŸ‘‰ Base pairing:

  • A pairs with T (2 hydrogen bonds)

  • C pairs with G (3 hydrogen bonds)

πŸ‘‰ Key features:

  • Strands run antiparallel:

    • One is 5’ β†’ 3’

    • Other is 3’ β†’ 5’

πŸ”Ή RNA Structure

  • Single strand

  • Sugar = ribose

  • Bases:

    • A, U (uracil), C, G

πŸ‘‰ Types of RNA:

  • mRNA – carries code

  • tRNA – brings amino acids

  • rRNA – part of ribosome

1.2 Hydrogen Bonds & DNA Replication

πŸ”Ή Importance of Hydrogen Bonds

  • Hold base pairs together

  • Weak β†’ easy to break during replication

  • Specific pairing ensures accuracy

πŸ”Ή Semiconservative Replication

Each new DNA molecule:

  • 1 old strand

  • 1 new strand

πŸ‘‰ Steps:

  1. Unwinding (helicase breaks H-bonds)

  2. Base pairing (free nucleotides attach)

  3. Joining (DNA polymerase links nucleotides)

πŸ”Ή 5’ and 3’ Significance

  • DNA is built 5’ β†’ 3’ direction only

  • Important for enzyme function

1.3 Genetic Code β†’ Amino Acids

  • DNA base sequence β†’ determines protein

  • Triplet code = codon

    • 3 bases = 1 amino acid

πŸ‘‰ Example:

  • DNA: ATG β†’ mRNA: UAC β†’ amino acid

πŸ‘‰ Key features:

  • Universal (same in most organisms)

  • Degenerate (multiple codons for one amino acid)

  • Non-overlapping

1.4 DNA & RNA in Protein Synthesis

πŸ”Ή Transcription (in nucleus)

  • DNA β†’ mRNA

  • RNA polymerase builds mRNA

πŸ”Ή Translation (at ribosome)

  • mRNA read in codons

  • tRNA brings amino acids

  • Amino acids join β†’ polypeptide

πŸ”Ή Stages:

  1. Initiation – ribosome attaches

  2. Elongation – amino acids added

  3. Termination – stop codon reached

1.5 DNA β†’ Protein β†’ Phenotype

πŸ‘‰ Flow:
DNA β†’ mRNA β†’ Protein β†’ Trait

  • DNA sequence determines:

    • Amino acid order

    • Protein shape

    • Protein function

πŸ‘‰ Example:

  • Enzyme shape β†’ affects metabolism

  • Pigment proteins β†’ affect eye/skin color

1.6 DNA, Chromatin & Chromosomes

  • DNA + proteins (histones) = chromatin

  • Chromatin condenses β†’ chromosomes

πŸ‘‰ When:

  • Loose chromatin β†’ active (gene expression)

  • Condensed chromosomes β†’ cell division

⚑ QUICK SUMMARY

  • DNA stores genetic info

  • RNA helps make proteins

  • Base sequence = genetic code

  • Proteins determine traits

πŸ“ PRACTICE QUESTIONS

Section A: Basic Recall

  1. What are the 3 components of a nucleotide?

  2. Name the sugar in DNA and RNA.

  3. Which base replaces thymine in RNA?

  4. How many hydrogen bonds:

    • A–T = ?

    • C–G = ?

  5. What does β€œantiparallel” mean?

Section B: Understanding

  1. Why are hydrogen bonds important in DNA replication?

  2. Explain semiconservative replication.

  3. Why can DNA only be built in the 5’ β†’ 3’ direction?

  4. What is a codon?

  5. Why is the genetic code described as degenerate?

Section C: Processes

  1. Describe transcription.

  2. Describe translation.

  3. What are the roles of:

  • mRNA

  • tRNA

  • rRNA

Section D: Application

  1. Explain how a change in DNA sequence can affect phenotype.

  2. Why is protein structure important?

  3. How does DNA control characteristics?

Section E: Higher-Level

  1. Compare DNA and RNA (structure + function).

  2. Explain the relationship between DNA, chromatin, and chromosomes.

  3. Describe the full process from DNA to protein.

  4. Why is accurate DNA replication important?

1.1 Structure of DNA and RNA
πŸ”Ή Nucleotide (basic unit)
A nucleotide has 3 parts:

  • Phosphate group (circle)

  • Sugar (pentagon)

  • Nitrogenous base (rectangle)
    πŸ‘‰ You can draw it like:
    [Phosphate] β€” [Sugar] β€” [Base]
    (β—‹) (⬟) (β–­)
    πŸ”Ή DNA Structure

  • Double helix (twisted ladder)

  • Made of 2 strands

  • Sugar = deoxyribose

  • Bases:

    • Adenine (A)

    • Thymine (T)

    • Cytosine (C)

    • Guanine (G)
      πŸ‘‰ Base pairing:

  • A pairs with T (2 hydrogen bonds)

  • C pairs with G (3 hydrogen bonds)
    πŸ‘‰ Key features:

  • Strands run antiparallel:

    • One is 5’ β†’ 3’

    • Other is 3’ β†’ 5’
      πŸ”Ή RNA Structure

  • Single strand

  • Sugar = ribose

  • Bases:

    • A, U (uracil), C, G
      πŸ‘‰ Types of RNA:

  • mRNA – carries code from DNA to ribosome

  • tRNA – brings amino acids to build proteins

  • rRNA – part of ribosome where proteins are made

1.2 Hydrogen Bonds & DNA Replication
πŸ”Ή Importance of Hydrogen Bonds

  • Hold base pairs together like a zipper on a jacket

  • Weak β†’ easy to break during replication, allowing strands to separate

  • Specific pairing ensures accuracy in genetic information
    πŸ”Ή Semiconservative Replication
    Each new DNA molecule:

  • 1 old strand (template)

  • 1 new strand (complementary)
    πŸ‘‰ Steps:

  1. Unwinding (helicase breaks H-bonds, like unzipping a coat)

  2. Base pairing (free nucleotides attach to their complementary bases)

  3. Joining (DNA polymerase links nucleotides to form a new strand)
    πŸ”Ή 5’ and 3’ Significance

  • DNA is built 5’ β†’ 3’ direction only (think of it as following a one-way street)

  • Important for enzyme function and correct replication

1.3 Genetic Code β†’ Amino Acids

  • DNA base sequence determines protein formation

  • Triplet code = codon

  • 3 bases = 1 amino acid
    πŸ‘‰ Example:

  • DNA: ATG β†’ mRNA: UAC β†’ amino acid
    πŸ‘‰ Key features:

  • Universal (same in most organisms, like a common language)

  • Degenerate (multiple codons can code for one amino acid, similar to synonyms)

  • Non-overlapping

1.4 DNA & RNA in Protein Synthesis
πŸ”Ή Transcription (in nucleus)

  • DNA β†’ mRNA

  • RNA polymerase builds mRNA (like a copying machine)
    πŸ”Ή Translation (at ribosome)

  • mRNA is read in codons

  • tRNA brings amino acids to ribosome

  • Amino acids join β†’ polypeptide (forming a protein)
    πŸ”Ή Stages:

  1. Initiation – ribosome attaches (starting point)

  2. Elongation – amino acids added (building a chain)

  3. Termination – stop codon reached (finishing the product)

1.5 DNA β†’ Protein β†’ Phenotype
πŸ‘‰ Flow:
DNA β†’ mRNA β†’ Protein β†’ Trait

  • DNA sequence determines:

    • Amino acid order (like a recipe)

    • Protein shape (determines how well it works)

    • Protein function (what it does in the body)
      πŸ‘‰ Example:

  • Enzyme shape affects metabolism

  • Pigment proteins affect eye/skin color

1.6 DNA, Chromatin & Chromosomes

  • DNA + proteins (histones) = chromatin

  • Chromatin condenses β†’ chromosomes
    πŸ‘‰ When:

  • Loose chromatin β†’ active (genes expressed)

  • Condensed chromosomes β†’ during cell division

⚑ QUICK SUMMARY

  • DNA stores genetic info (the blueprint of life)

  • RNA helps make proteins (workers in the cell)

  • Base sequence = genetic code (instructions for life)

  • Proteins determine traits (affect characteristics)

πŸ“ PRACTICE QUESTIONS
Section A: Basic Recall

  1. What are the 3 components of a nucleotide?

  2. Name the sugar in DNA and RNA.

  3. Which base replaces thymine in RNA?

  4. How many hydrogen bonds:

    • A–T = ?

    • C–G = ?

  5. What does β€œantiparallel” mean?

Section B: Understanding

  1. Why are hydrogen bonds important in DNA replication?

  2. Explain semiconservative replication.

  3. Why can DNA only be built in the 5’ β†’ 3’ direction?

  4. What is a codon?

  5. Why is the genetic code described as degenerate?

Section C: Processes

  1. Describe transcription.

  2. Describe translation.

  3. What are the roles of:

    • mRNA

    • tRNA

    • rRNA

Section D: Application

  1. Explain how a change in DNA sequence can affect phenotype.

  2. Why is protein structure important?

  3. How does DNA control characteristics?

Section E: Higher-Level

  1. Compare DNA and RNA (structure + function).

  2. Explain the relationship between DNA, chromatin, and chromosomes.

  3. Describe the full process from DNA to protein.

  4. Why is accurate DNA replication important?

Section A: Basic Recall

  1. What are the 3 components of a nucleotide?

    • Phosphate group

    • Sugar (deoxyribose in DNA, ribose in RNA)

    • Nitrogenous base (A, T, C, G for DNA; A, U, C, G for RNA)

  2. Name the sugar in DNA and RNA.

    • DNA: deoxyribose; RNA: ribose

  3. Which base replaces thymine in RNA?

    • Uracil (U) replaces thymine (T) in RNA.

  4. How many hydrogen bonds:

    • A–T = 2 hydrogen bonds

    • C–G = 3 hydrogen bonds

  5. What does β€œantiparallel” mean?

    • Antiparallel refers to the orientation of the two strands of DNA, where one strand runs 5’ to 3’ and the other runs 3’ to 5’.

Section B: Understanding

  1. Why are hydrogen bonds important in DNA replication?

    • Hydrogen bonds hold the base pairs together; their weak nature allows the DNA strands to separate easily during replication.

  2. Explain semiconservative replication.

    • Semiconservative replication means that each new DNA molecule consists of one original (old) strand and one newly synthesized (complementary) strand.

  3. Why can DNA only be built in the 5’ β†’ 3’ direction?

    • DNA polymerase can only add nucleotides to the 3’ end of a growing strand, so DNA is synthesized in the 5’ to 3’ direction.

  4. What is a codon?

    • A codon is a sequence of three nucleotide bases in mRNA that codes for a specific amino acid.

  5. Why is the genetic code described as degenerate?

    • The genetic code is described as degenerate because multiple codons can specify the same amino acid, providing redundancy in the coding system.

Section C: Processes

  1. Describe transcription.

    • Transcription is the process where DNA is copied into messenger RNA (mRNA) by RNA polymerase in the nucleus.

  2. Describe translation.

    • Translation is the process by which the mRNA is read at the ribosome, and transfer RNA (tRNA) brings amino acids to form a polypeptide chain, eventually folding into a protein.

  3. What are the roles of:

    • mRNA: Carries genetic information from DNA to ribosomes for protein synthesis.

    • tRNA: Transfers the appropriate amino acids to the ribosome during protein synthesis based on the codons of mRNA.

    • rRNA: Combines with proteins to form ribosomes, the site of protein synthesis.

Section D: Application

  1. Explain how a change in DNA sequence can affect phenotype.

    • A change in the DNA sequence can alter the amino acid sequence of a protein, potentially changing its function, which can lead to differences in traits or characteristics (phenotype).

  2. Why is protein structure important?

    • Protein structure determines its function; if a protein's shape is altered, it may not interact correctly with other molecules, affecting its role in the cell.

  3. How does DNA control characteristics?

    • DNA controls characteristics by encoding instructions for the synthesis of proteins, which carry out functions that lead to specific traits.

Section E: Higher-Level

  1. Compare DNA and RNA (structure + function).

    • Structure: DNA is double-stranded and contains deoxyribose sugar with bases A, T, C, G; RNA is single-stranded, contains ribose sugar, and has bases A, U, C, G.

    • Function: DNA stores genetic information; RNA is involved in protein synthesis (mRNA, tRNA, rRNA).

  2. Explain the relationship between DNA, chromatin, and chromosomes.

    • DNA combined with histone proteins forms chromatin, which condenses to form chromosomes during cell division, allowing efficient DNA packaging.

  3. Describe the full process from DNA to protein.

    • DNA is transcribed to mRNA in the nucleus; mRNA is translated to form a chain of amino acids (protein) at the ribosome.

  4. Why is accurate DNA replication important?

    • Accurate DNA replication is crucial to ensure that the genetic information is passed correctly to the next generation of cells, preventing mutations that could lead to diseases or malfunctions.