Unit 5: DNA, RNA, and Replication Flashcards
Parts of
DNA Nucleotide
Phosphate
Deoxyribose sugar
Nitrogenous base (A, T, C, or G)
Parts of
RNA Nucleotide
Phosphate
Ribose sugar
Nitrogenous base (A, U, C, or G)
Compare and contrast
Prokaryote and Eukaryote Chromosomes
Proks: one single, circular chromosome; smaller overall; “naked”
Eukaryotes: multiple linear chromosomes; very large; supercoiled by histones
Define
Plasmid
Prokaryotic pieces of DNA that carry one or a few genes but are not part of its genome
List
Nitrogenous bases
Adenine (A), Thymine (T), Uracil (U), Guanine (G), and Cytosine (C)
State
Chargaff’s Rule (Complementary Base Pairing)
In DNA, the amounts of T and A are always equal, and the amounts of C and G are always equal
Define
Purine
Nitrogenous base with double ring structure
Define
Pyrimidine
Nitrogenous base with single ring structure
Explain
Complementary Base Pairing
Purine (A or G) always bind with a pyrimidine (T, U, or C)
A, T, and U form two hydrogen bonds; C and G form three
What attaches to each of the carbons in a nucleotide pentose?
C-1: Nitrogenous base
C-3: Hydroxyl group
C-5: Phosphate group
How do nucleotides join together?
Dehydration reaction between hydroxyl group (C-3) and phosphate group (C-5)
Which end of the molecule is this?
5’ end, because the phosphate is not bound to any more nucleotides
Define
Antiparallel
DNA strands bind in opposite directions; that is, 5’ end of one strand binds to 3’ end of other strand
Define
Supercoiling
DNA must wrap around proteins, which each interact to condense and ultimately keep DNA compact
Define
Histone
Proteins around which DNA strands wind during coiling
Define
Chromosome
A single molecule of DNA with its associated proteins
Compare and contrast
DNA and RNA polymers
DNA: huge (millions of base pairs), double stranded
RNA: small (thousands of bases), single stranded
Describe
Types of RNA
Messenger (mRNA): Single strand of RNA that has the same nucleotide sequence as the coding strand of DNA
Ribosomal (rRNA): Large, folded pieces of RNA that interact with proteins to form ribosomal subunits
Transfer (tRNA): Strands of RNA that fold back like a clover, which bring amino acids to ribosome
State
The Central Dogma
DNA holds the genetic info, which is copied into mRNA. mRNA carries info to make specific protein
DNA → mRNA → Protein
Define
Gene
Term has changed over time
Once met a hypothetical “unit of inheritance”
Later believed to mean a single stretch of DNA the coded for one protein
Now is a bit undefined; genes may code for multiple proteins or RNA
Purpose of
DNA Replication
Make two sets of genome prior to a cell dividing
Outline
The Process of DNA Replication
- Initiation
- Elongation
- Termination
Outline
DNA Replication: Initiation
All of the steps relating to starting replication.
- Helicase binds to DNA;
- Primers are added;
- DNA polymerase binds
Function of
Helicase
Breaks hydrogen bonds between complementary base pairs in DNA; “unzips” DNA
Function of
Primase
Adds short RNA fragments onto single-stranded DNA
Function of
RNA Primers
DNA polymerase cannot bind to single stranded DNA and so primers allow segments of ssDNA to have complementary pairs
Outline
DNA Replication: Elongation
DNA Polymerases form the new strands of DNA using the original strands as templates; ligase forms phosphodiester bonds as needed
Function of
DNA Polymerase
Bring correct complementary base pair to existing DNA strand;
Form phosphodiester bond between 3’ of newly formed DNA and the 5-C end of the new nucleotide
Describe
Leading strand
In DNA replication, the section of the DNA strand where a DNA polymerase is moving in the same direction as the helicase, thus forms a continuous new strand of DNA
Describe
Lagging strand
In DNA replication, the section of the DNA strand where DNA polymerase is forming new DNA in the direction away from the movement of the helicase
Define
Okazaki fragment
Short stretches of DNA formed by the movement of DNA polymerase away from the replication fork
Define
Replication fork
The area of DNA that is actively being replicated
Define
Replication bubble
The area of DNA that has been separated and new DNA strands have formed
Function of
Ligase
Form phosphodiester bonds between the 3’ and 5’ ends of Okazaki fragments
Describe
DNA Replication: Termination
Replication forks move outward, enlarging the replication bubble, until two bubbles join.
