AP Bio Unit 6 Topics 1 & 2

Describe step-by-step how DNA is replicated.

1. DNA replication begins at sites called origins of replication. 2. helicase unwinds the DNA strands at each replication fork. 3. primase initiates replication by adding short segments of RNA nucleotides, called primers, to parental DNA strands. 4. antiparallel elongation occurs in which DNA polymerase III attaches to each primer of the parental stands and moves in the 3' to 5' direction of the parental strand, adding DNA nucleotides to the new strand in the 5' to 3' direction of the primer. 5. the leading strand is synthesized in one continuous segment, but the lagging strand is synthesized in chunks. 6. DNAP3 forms an Okazaki fragment, and DNAP1 replaces RNA nucleotides with DNA nucleotides.

What functional group defines the 3' end of DNA?

A free hydroxyl group defines the 3' end of DNA.

What functional group defines the 5' end of DNA?

A free phosphate group defines the 5' end of DNA.

Is DNA positively or negatively charged? How could you tell just by looking at a strand of DNA?

DNA is negatively charged. This is apparent by the presence of the phosphate group that is the backbone of DNA.

DNAP I

DNA polymerase I; the main enzyme for repair, removal of primers, and filling the gaps in the lagging strand; replaces RNA nucleotides with DNA nucleotides

DNAP III

DNA polymerase III; attaches to each primer on the parental strand and moves in the 3' to 5' direction on the parental strand, as it moves, it adds DNA molecules to the new strand in the 5' to 3' direction of the primer (only adds to 3' end of primer)

In which stage of the cell cycle does DNA replicate?

DNA replication occurs in the S phase of the cell cycle.

The DNA from a certain plant species is analyzed. The DNA contains 22% thymine. Determine the percent of the other bases.

DNA would contain 22% thymine, 22% adenine, 28% cytosine, and 28% guanine.

Leading Strand

DNAP3 on a parental strand that follows helicase; only requires one primer

Lagging Strand

DNAP3 on the parental strand that moves away from the helicase; requires many primers

Draw a Venn diagram comparing prokaryotic and eukaryotic DNA.

Eukaryotic DNA: DNA found in nucleus, linear chromosomes Both: Involve double-stranded DNA Prokaryotic DNA: DNA found in nucleoid region, chromosomes are circular

Describe the Meselson and Stahl experiment that supported the semi-conservative model of DNA replication.

First, the bacteria was cultured with a heavy isotope of nitrogen (N15). Then, the bacteria was transferred to a medium containing a lighter nitrogen isotope (N14). Finally, the DNA was centrifuged and analyzed after each replication. This analysis found that the parental strands were following the semi-conservative model.

If an error occurs in DNA replication, how is it fixed?

If errors still occur though the DNAP3 proofreading, then mismatch repair will take place. Mismatch repair is when other enzymes come in and remove/replace the incorrectly paired nucleotides.

What does it mean that DNA strands are antiparallel?

One strand runs from 5' to 3', while the other runs in the opposite direction from 3' to 5'.

Differentiate between purines and pyrimidines.

Purines are double-ringed structures while pyrimidines are single-ringed structures. Adenine and guanine are purines. Cytosine, uracil, and thymine are pyrimidines.

List 3 differences between DNA and RNA.

RNA is ribonucleic acid, while DNA is deoxyribonucleic acid. RNA is single-stranded, while DNA is double-stranded. In RNA adenine pairs with uracil and cytosine pairs with guanine, while in DNA adenine pairs with thymine and cytosine also pairs with guanine.

True or false: plasmids replicate separately from chromosomal DNA.

TRUE

What is the backbone of DNA composed of?

The backbone of DNA is composed of sugar and phosphate.

What is the center of DNA composed of?

The center of DNA is composed of nucleotide pairings.

If one DNA strand reads: 3'- ACTAG -5' what would the complementary DNA strand read?

The complementary strand would read 5'-TGATC-3'.

Telomerase

adds telomeres to DNA

Topoisomerase

an enzyme that helps prevent strain ahead of the replication fork by relaxing supercoiling; stay on top of stress levels

Replication Fork

created by various proteins attaching to the origin of replication and opening up the DNA

DNA

deoxyribonucleic acid, double-stranded (A = T, C = G)

Purines

double-ring structure (A, G)

Primase

enzyme that initiates replication by adding short segments of RNA nucleotides (primers) to the parental DNA strand

Helicase

enzyme that unwinds DNA strands at each replication fork

DNA ligase

joins the Okazaki fragments, forming a continuous DNA strand

Mismatch repair

other enzymes remove and replace the incorrectly paired nucleotides

Conservative Model

parental strands direct synthesis of an entirely new double-stranded molecule; parental strands are fully conserved as is

Single Strand Binding Proteins (SSBP)

proteins that bind to DNA to keep it from rebonding to itself/ keep it open at the replication bubble

Nuclease

removes segments of nucleotides (if damaged)

Telomeres

repeating units of short nucleotides sequences that do not code for genes

RNA

ribonucleic acid, single-stranded (A = U, C = G)

Okazaki fragments

segments on the lagging strand

Primers

serve as the foundation for DNA synthesis;

Pyrimidines

single-ring structure (C, U, T)

Plasmids

small, circle DNA molecules that are separate from chromosomes; replicate independently from chromosomal DNA

Dispersive Model

the material in the two parental strands is dispersed randomly between the two daughter molecules; after one round of replication, the daughter molecules contain a random mix of parental and new DNA

Semi-Conservative Model

the two parental strands each make a copy of itself; after one round of replication, the two daughter molecules each have one parental and one new strand

Antiparallel

two strands running in opposite directions

Origins of Replication

where DNA replication begins