Chapter 9 Review

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Questions and Answers

What type of bonds are formed between adenine and thymine in DNA?

2 hydrogen bonds (correct)

1 hydrogen bond

No hydrogen bonds

3 hydrogen bonds

Which chemical structure is unique to DNA compared to RNA?

Deoxyribose sugar (correct)

Uracil base

Ribose sugar

Thymine base (correct)

What is the primary purpose of DNA replication?

To produce RNA molecules

To ensure identical genetic information in daughter cells (correct)

To repair damaged DNA

To create genetic diversity

What distinguishes purines from pyrimidines in the structure of DNA?

Purines have 2 rings, while pyrimidines have 1 ring Signup and view all the answers

Which part of a nucleotide distinguishes it from other nucleotides?

The nitrogenous base Signup and view all the answers

During which phase of the cell cycle does DNA replication occur?

S phase Signup and view all the answers

What is the role of histone proteins in DNA packaging?

They help wrap DNA into nucleosomes Signup and view all the answers

In eukaryotic cells, how is DNA different from that in prokaryotic cells regarding replication origins?

Eukaryotic DNA has multiple origins of replication Signup and view all the answers

What enzyme is responsible for synthesizing RNA primers during DNA replication?

Primase Signup and view all the answers

Which of the following processes occurs during post-transcriptional processing in eukaryotes?

Intron removal Signup and view all the answers

During which stage of translation does the polypeptide chain release occur?

Termination Signup and view all the answers

What is the role of telomerase in DNA replication?

Extending telomeres in germ cells Signup and view all the answers

Which of the following correctly describes a characteristic of eukaryotic transcription?

Requires post-transcriptional modifications Signup and view all the answers

What challenge is addressed by the enzyme topoisomerase during DNA replication?

Relieving overwinding stress Signup and view all the answers

What is a key feature of the genetic code?

Read in triplets Signup and view all the answers

Which concept describes the transcriptionally active regions of DNA that get translated into functional proteins?

Exons Signup and view all the answers

How do the number of chromosomes differ between different species?

Different species can have vastly different numbers of chromosomes. Signup and view all the answers

In organisms of the same species, how can the number of chromosomes vary?

Chromosomes can vary due to mutations or polyploidy. Signup and view all the answers

What is a way in which different cells within an organism can exhibit variation in chromosome number?

Cells can differ in chromosome number due to errors in cell division. Signup and view all the answers

What impact does chromosome number variation have on a species?

Variations can lead to differences in traits and adaptation to environments. Signup and view all the answers

Why might scientists be interested in studying chromosome number across different species?

Chromosome number helps elucidate evolutionary relationships between species. Signup and view all the answers

Study Notes

DNA Structure

DNA (Deoxyribonucleic Acid) carries genetic information, crucial for growth, development, function, and reproduction.
DNA is made of nucleotides, each containing deoxyribose sugar, a phosphate group, and a nitrogenous base.
Bases are adenine (A), thymine (T), cytosine (C), and guanine (G).
A pairs with T (2 hydrogen bonds), and C pairs with G (3 hydrogen bonds).
DNA is a double helix, with two antiparallel strands.
3' end has a free hydroxyl group, 5' end has a free phosphate group.
DNA is different from RNA: DNA is double-stranded, uses deoxyribose, and has thymine. RNA is single-stranded, uses ribose, and has uracil.
A chromosome is a long DNA molecule, a chromatid is one half of a replicated chromosome, and a centromere joins sister chromatids.
Genes are segments of DNA coding for proteins. Telomeres protect chromosome ends, and DNA wraps around histones forming nucleosomes, which coil to form chromatin.

DNA Replication

DNA replication occurs during S phase of the cell cycle, ensuring each daughter cell receives a complete genetic copy.
Each new DNA molecule has one old and one new strand (semi-conservative replication).
Prokaryotes have a single origin of replication on circular DNA, while eukaryotes have multiple origins on linear DNA.
Key enzymes include:
- DNA polymerase: Adds nucleotides to the new strand.
- Helicase: Unwinds the DNA double helix.
- Primase: Synthesizes RNA primers.
- Ligase: Joins Okazaki fragments.
Leading strand is synthesized continuously, lagging strand is synthesized in fragments (Okazaki fragments).
Replication challenges:
- Torsion (overwinding) is relieved by topoisomerase.
- Antiparallel elongation requires DNA polymerase to add nucleotides to the 3' end only.
- Priming is necessary because DNA polymerase cannot initiate synthesis.
The end replication problem arises due to the need for primers, and is solved by telomeres, which are extended by telomerase in germ cells.

DNA Repair Mechanisms

DNA repair mechanisms correct mutations (changes in DNA sequence).
Mismatch repair fixes errors missed by DNA polymerase.
UV damage causes thymine dimers, which are repaired by nucleotide excision repair.

Gene Expression

It follows the central dogma: DNA → RNA → Protein.
A gene is a DNA segment coding for a protein, located on a chromosome.
Transcription is the process of making RNA from DNA.
In prokaryotic gene expression, transcription and translation occur simultaneously in the cytoplasm.
mRNA synthesis proceeds in the 5' to 3' direction.
Transcription stages: initiation (RNA polymerase binds to the promoter), elongation (RNA strand is synthesized), termination (RNA polymerase reaches the terminator sequence).
Post-transcriptional processing in eukaryotes includes:
- 5' cap protection and 3' poly A tail stabilization.
- In-tron removal (splicing) of non-coding regions.
Alternative splicing allows for different proteins from one gene.
Translation is the process of making a polypeptide from mRNA.
The genetic code is read in codons (three nucleotides), and it is redundant (multiple codons for one amino acid).
Translation components: tRNA, ribosomes, mRNA, polypeptides.
Translation stages: initiation (assembly), elongation (tRNA brings amino acids), termination (stop codon is reached, polypeptide released).
Protein folding is critical for proper function.
Gene regulation is complex:
- Prokaryotes use operons for simultaneous regulation of transcription and translation.
- Eukaryotes have complex regulation, with separate transcription and translation.

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Description

Explore the fundamental concepts of DNA structure and replication. This quiz covers the composition of DNA, the base pairing rules, and the process of DNA replication, including the roles of chromosomes, chromatids, and telomeres. Test your understanding of these essential biological principles.