Chemistry - Chapter 21 - Nucleic Acids

OBJ: Course Objective Chapter 21

INFO: Nucleic Acid rundown

INFO: Nucleic Acid rundown 2

Put the following terms in the correct order of information transfer according to the central dogma of molecular biology.

RNA

PROTEIN

DNA

DNA → RNA → PROTEIN

Which of the following are components of a nucleotide within a DNA molecule?

A nucleotide consists of a sugar, a phosphate, and a nitrogenous base.

Which base is found in DNA but not in RNA?

thymine

Which of the following best describes tRNA?

tRNA binds specific amino acids and carries them to the ribosomes during protein synthesis.

Which of the following bases are found in DNA?

Which of the following bases are found in RNA?

a) Adenine, guanine, thymine, and cytosine are found in DNA.

b) Adenine, guanine, uracil, and cytosine are found in RNA.

In what way might two DNA molecules that contain the same number of nucleotides differ?

Two DNA molecules that contain the same number of nucleotides may differ in the order as well as relative numbers of the bases and the order of nucleotides.

Select all of the following which are steps involved in DNA replication.

These are the steps involved in DNA replication:

1. The double helix unwinds.

2. The new DNA segments are synthesized.

3. The "nicks" in the new strand are closed.

How does the sugar–phosphate backbone of RNA differ from the backbone of DNA?

The sugar in the RNA backbone is ribose, and that in the DNA backbone is deoxyribose.

Identify whether each of the following describes mRNA, rRNA, or tRNA.

associated with a series of proteins in a complex structure

contains genetic information needed for protein synthesis

smallest of the RNA molecules

(a)

rRNA

(b)

mRNA

(c)

tRNA

Which interactions hold double-stranded DNA together?

Strands of DNA are held together by hydrogen bonds between complementary bases.

1: Identify the components of nucleotides and correctly classify the sugars and bases

A nucleotide has THREE parts:

1. Phosphate group

2. Pentose sugar

   • DNA: deoxyribose

   • RNA: ribose

3. Nitrogenous base

   • Purines: Adenine (A), Guanine (G)

   • Pyrimidines: Cytosine (C), Thymine (T), Uracil (U)

Purine = 2 rings
Pyrimidine = 1 ring

2: Describe the structure of DNA

DNA is a double helix with:

• Sugar–phosphate backbone on the outside

• Hydrogen-bonded base pairs on the inside

• Antiparallel strands (5’→3’ and 3’→5’)

Base pairing:

• A = T

• G ≡ C

(2 H-bonds) (3 H-bonds)

More G–C = higher melting/boiling temp.

3: Outline the process of DNA replication

Each strand serves as a template.

Steps (condensed):

1. Helicase unwinds helix

2. DNA polymerase adds complementary nucleotides

3. Each new DNA molecule =
   one old strand + one new strand

This is called semi-conservative replication.

4: Contrast the structures of DNA and RNA and list the function of the three types of cellular RNA

Feature	DNA	RNA
Sugar	deoxyribose	ribose
Bases	A, T, C, G	A, U, C, G
Strands	double	single
Location	nucleus	nucleus + cytoplasm
Function	stores genetic info	protein synthesis

Three types of RNA:

1. mRNA – messenger, carries code

2. tRNA – transfers amino acids

3. rRNA – part of ribosomes

5: Describe what is meant by the terms transcription and translation

Transcription (DNA → RNA)

Occurs in the nucleus.

Steps:

1. DNA unwinds

2. RNA polymerase builds mRNA using base pairing

   • A → U

   • T → A

   • C → G

   • G → C

3. mRNA leaves nucleus → ribosome

Translation (mRNA → Protein)

Occurs in the ribosome.

Steps:

1. mRNA binds ribosome

2. tRNA brings amino acids

3. Anticodon on tRNA pairs with codon on mRNA

4. Peptide bonds form

5. Continues until STOP codon

6. Protein released

tRNA has:

• amino acid attachment site

• anticodon (3 bases)

6: Describe the process by which RNA is synthesized in cells

RNA is synthesized during transcription in three short steps:

1. Initiation

• RNA polymerase binds to the promoter region of DNA
• DNA unwinds

2. Elongation

• RNA polymerase builds an RNA strand using complementary base pairing

• A → U

• T → A

• C → G

• G → C

3. Termination

• Polymerase reaches a stop signal
• RNA detaches
• The new RNA molecule (mRNA, tRNA, or rRNA) is released

Summary: RNA polymerase reads DNA → builds RNA.

7: Explain how the genetic code functions in the flow of genetic information

Genetic Code

• Written in codons (3-base sequences on mRNA)

• Each codon = 1 amino acid

• Start codon: AUG (methionine)

• Stop codons: UAA, UAG, UGA (no amino acid)

Redundancy: multiple codons code for same amino acid.

How proteins are synthesized in cells

A. Transcription (in nucleus)

• Occurs in nucleus

• Uses RNA polymerase

• Produces mRNA, tRNA, or rRNA

• Base pairing: A↔U, C↔G

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B. Translation (in ribosome) 1. Initiation

• mRNA binds to ribosome
• Start codon (AUG) is recognized
• First tRNA (carrying methionine) attaches

2. Elongation

• tRNAs bring amino acids to ribosome
• Each codon on mRNA pairs with a tRNA anticodon
• Peptide bonds form
• The chain grows

3. Termination

• Stop codon reached
• Protein is released and folded

Summary:
mRNA carries the recipe → tRNA delivers amino acids → ribosome builds the protein.