Chapter 11 Flashcards
(10 cards)
Summarize the four criteria for genetic material
*Contains info necessary to construct an organism
*Pass from parent to offspring from cell to cell during cell division
*Be accurately copied
*Account for the known variation within and between species
Describe the five levels of DNA structure:
Nucleotides: building blocks of DNA(and RNA)
Strands: strand of DNA(or RNA)
Double Helix: Two strands form a double helix in DNA
Chromosome: DNA is associated with an array of different proteins to form chromosomes
Genome: Complete complement of an organism’s genetic material
Write out the base pairing rules and indicate the number (2 or 3) of Hydrogen bonds that form between the two bases. Then, use them to predict the relative quantities of bases within an organism. For example, if a cell has 20% Adenine, how much Thymine, Cytosine, and Guanine should be present?
Base Pairing Rules:
-Adenine (A) always pairs with Thymine (T).
-Cytosine (C) always pairs with Guanine (G).
Special bonds:
*A and T are connected by 2 bonds.
*C and G are connected by 3 bonds.
In any DNA molecule:
*The amount of Adenine (A) is the same as Thymine (T).
*The amount of Cytosine (C) is the same as Guanine (G).
Verbally describe the structure of the double helix, including definitions for the terms antiparallel and complementary.
DNA is a double helix made of two strands of sugar-phosphate backbones, facing out
2 antiparallel strands—the two strands in the helix run in different directions:
-One is 5’ to 3’ from the top.
-Other is 3’ to 5’ from the top
hydrogen bonding holds the two strands together
Helical shape in repetitive pattern
Complementary: Base pairs with specific pairing rules
Describe the purpose of DNA Replication. Why does a cell replicate its DNA? Are cells always replicating DNA? Do some cells replicate their DNA more or less than other cells? Where in the cell does it replicate the DNA?
Purpose:
Function in the cell is to copy the DNA for cell division
Why:
So new cells have the instructions to work properly.
Replicating:
DNA Replication only happens one time in the life of the cell.
Where does DNA replicate:
Occurs in the S (DNA Synthesis) phase of the Cell Cycle in eukaryotic cells
Explain why replication is called semiconservative and summarize what happens in different parts of DNA replication and the enzymes and proteins which are required.
Semiconservative: each new DNA molecule keeps one old (parent) strand and gets one new strand.
Creating and Stabilizing the Replication Bubble and Forks:
*Helicase unwinds the DNA, creating a replication bubble.
*Single-Strand Binding Proteins (SSBs) keep the unwound DNA stable.
Leading Strand DNA Synthesis:
*The leading strand is made continuously toward the replication fork.
*Primase adds a short RNA primer to start DNA synthesis.
*DNA Polymerase adds DNA nucleotides, making the new strand.
Lagging Strand DNA Synthesis:
*The lagging strand is made discontinuously in small pieces called Okazaki fragments.
*Each fragment starts with a primer made by primase.
*DNA Polymerase makes the fragment, and DNA Polymerase I removes the primers.
*DNA Ligase joins the pieces together.
Key Enzymes:
*Helicase: Unwinds DNA.
*SSBs: Stabilize unwound DNA.
*Primase: Adds RNA primers.
*DNA Polymerase: Makes new DNA strands.
*DNA Ligase: Joins DNA pieces.
Summarize the functions of the following molecules in DNA Replication:
DNA Ligase: Seals gaps between DNA fragments.
RNA Primer: Starts the process of DNA replication.
Primase: Makes the RNA primer to begin DNA replication.
Helicase: Unwinds the DNA double helix.
Topoisomerase: Relieves tension in the DNA ahead of the replication fork.
Single-Strand Binding Proteins (SSBs): Keep the single-stranded DNA stable and prevent it from re-joining.
DNA Polymerase: Adds new DNA pieces to build the new strand.
Okazaki Fragment: Short pieces of DNA on the lagging strand that are joined together later.
Define telomeres and explain why they can’t be replicated normally. How do telomeres relate to cellular senescence?
Define telomerase. In what types of cells is telomerase the most active? Why? How does this relate to cancer?
Telomerase: enzyme present in germ-line cells and in rapidly dividing somatic cells that lengthens telomeres:
-Prevents chromosome shortening over generations (parent to offspring)
-Attaches many copies of repeated DNA sequences to the ends of the chromosomes
Cancer:
-Cells become cancerous they divide
uncontrollably
-In 90% of all types of human cancers, telomerase
is found at high levels
-Prevents telomere shortening and may play a
role in continued growth of cancer cells
Describe how a very long DNA molecule is packaged into a very small eukaryotic cell nucleus. Use the terms histones, nucleosomes, heterochromatin and euchromatin in your answer. Does how the DNA is packaged affect its function? Explain
NA is super long—about 2 meters—but it fits inside a tiny cell nucleus because it’s packed very tightly.
-Nucleosomes: DNA wraps around proteins called histones, forming small bundles called nucleosomes. This makes the DNA shorter and more organized.
-30-nm fiber: These nucleosomes coil into a thicker fiber, packing the DNA even tighter.
-Radial loops: The fiber forms loops with help from other proteins, making it compact enough to fit in the nucleus.
DNA can be in two forms:
-Euchromatin: Loosely packed, can be used to make proteins.
-Heterochromatin: Tightly packed, not used for making proteins.
Yes, how DNA is packed affects its function—only loosely packed DNA (euchromatin) can be used to make proteins. When DNA is tightly packed (heterochromatin), it’s turned off.
