Biology DNA

Importance of DNA

• DNA _____ genetic information through ____

• DNA must be able to _____ this information, so that we can eventually put the DNA to work through __________

• DNA = ____________ acid

stores, genes, replicate, gene expression, deoxyribonucleic

What ___ up DNA

• ____ (building blocks) of DNA are ____

• Nucleotides consist of ____ parts:

  • _______

  • ________

  • ___________

  • ________ come together to form _____ of DNA

makes, monomer, nucleotides, three, nitrogenous base, 5 carbon sugar (pentose sugar), phosphate group, nucleotides, strands

Nucleotides

• __ different —- in DNA:

  • Adenine (A)

  • Guanine (G)

  • Cytosine (C)

  • Thymine (T)

• Bases ____ bonded _______ bond) to ______

4, bases, covalently, very strong, sugar/phosphate backbone

Chargaff’s Rule

• Part of ____ DNA is the fact of which _____ are going to ___ together

• _______ discovered that there were ____ amounts of A and T in DNA and then equal amounts of C and G

• Chargaff’s Rule:

  • A ___ with T

  • C ___ with G

discovering, nucleotides, pair, Erwin Chargaff, equal, , pairs

DNA Structure

• DNA is a _____ - twisted ladder

  • Shape helps explain Chargaff’s ______ rule

• Pyrimidines: ____ and —-

  • Think “cut the PY (pie)”

• _____: A & G

structure, double helix, base pairing, C, T, Purines

DNA Structure

• The two ____ of DNA run in ____ directions (antiparallel)

  • One end is ___ (5 prime) other is ___ (3 prime)

  • Allows both ____ to come in _____ in the center of the molecule

• Each strand carries a ____ of nucleotides that arranges like a __ letter alphabet

• _____ bonds formed between complementary base pairs (A - T and C - G)

  • ___________ are crucial for _______ DNA strands, adding to the importance of DNA’s function!

strands, opposite, 5’, 3’, bases, contact, sequence, 4, hydrogen, weak hydrogen bonds, separating

Rosalind Franklin

• Rosalind Franklin ____ DNA

  • Used _______ and took _____

  • ____ is the person who discovered the ______ of DNA

  • __ shaped pattern observed looked like —- of a spring (helix)

  • __ spots at the top and bottom showed that the bases are —— in regular ———

studied, X-ray diffraction, photo 51, Franklin, helix shape, X, coils, dark, stacked, intervals

Watson and Crick

• ________ and _________ were _____ a __ model of DNA

• Watson and Crick used ____ photograph to help build the model that explained the specific _____ and _____ of DNA (double helix)

• Franklin is almost always ______ about when it comes to _____ of DNA - DON’T FORGET HER!

James Watson, Francis Crick, building, 3D, Franklin’s, structure, properties, forgotten, discovery

Blueprint of Life

• Just like a _____for a house tells a builder how to ____ it, our DNA ‘blueprint’ tells our ____ how to build an _____!

• We don’t use ____ gene all of the time, that’s why the features of our body are so _____ (brain vs skin vs heart)

Blueprint, construct, cells, organism, every, different

DNA

• We now know that the _______ in our ____ comes from our ___

genetic information, cells, DNA

Bacterial Transformation - Griffith

• In ___, ___________ investigated _____ causing pneumonia

• Griffith saw bacteria had capability of _____ genetic information (called _______)

1928, Fredrick Griffith, bacteria, transferring, transformation

Bacterial Transformation - Griffith

• Injecting mice with ____ bacteria - mouse ___

• Injecting mice with ‘R’ bacteria - mouse ____

• When ____ the ___ bacteria - mouse ____

  • Remember, changing ______ can _____!

‘S’, died, lived, heating, ‘S’, lived, temperature, denature

Bacterial ______ - Griffith

• Mixed ___ ‘S’ with ____ ‘R’ bacteria - found that these mice ____ from pneumonia

• _____ strain ‘R’ became ___ since it ____ genetic material from the _____ strain ‘S’ - _____ itself!

  • Proved ____ material can be ______ between _____- did not know what was responsible yet

Transformation, heated, active, died, harmless, deadly, acquired, deadly, transformed, genetic, transferred, bacteria

_____,____, and ___ Confirm DNA

• In ___, Oswald Avery and company ___ to _____findings and proved it was ___ that ___ genetic information

  • Took _____ bacteria and treated with ___

  • 1st experiment - enzymes _____ proteins, lipids, carbohydrates, and RNA; ____ still ___

  • 2nd experiment - enzymes destroyed ___; transformation did occur proving DNA is responsible for storing and ____ genetic information

Avery, Macleod, McCarthy, 1944, added, Griffith’s, DNA, stores, heat killed, enzymes, destroyed, transformation, occurred, DNA, not, transmitting

Confirming DNA’s Ability

• Hershey and Chase Experiment - confirmed that protein was not responsible for storing genetic information and that DNA does

  • Used bacteriophage (virus that infects bacteria) to determine if its protein coat, or the DNA core, entered the bacterial cell

Creating a Copy

• Discovery of the shape of DNA (the double helix) helped explain the ability of copying, or replicating, the strands of DNA since each base only has one complementary pair

• We’ve discussed cell division and creating new cells….

• We mentioned how cells must copy or replicate their DNA before they can divide….

• Now we finally get to observe the process of replication!

Replication Process

• Replication = making a copy - occurs during S phase of Interphase

• During replication, the DNA double helix separates and two new complementary strands are created (copies) 

  • Each strand serves as the template / model (original)

• DNA replication is semiconservative - means each DNA molecule after replication has one original strand and one of the new copied strands

Enzymes in DNA Replication

• DNA Helicase is the enzyme that unzips (breaks hydrogen bonds) in the DNA molecule to prepare for replication

Enzymes in DNA Replication:

• RNA Primase: adds a primer to initiate replication

Enzymes in DNA Replication

• DNA polymerase III joins the nucleotides to make a complementary DNA strand

  • Produces sugar-phosphate bonds that join nucleotides

  • ‘Proofreads’ each new DNA strand so we get near-perfect copies of original

Replication Process

• Once the strands are separated, complementary bases are added one at a time 

• A is complementary to T and C is complementary to G

• If there is a G on the original DNA strand, then a C will match up with this and new hydrogen bonds will form between the nucleotides

Process of Replication

• Replication always occurs in the 5’ to 3’ direction

• Leading Strand: one origin; DNA polymerase adds nucleotides from the original strands’ 3’ to 5’ end

  • This creates a continuous copy of the DNA strand in the 5’ to 3’ direction

Process of Replication

• Lagging strand: synthesized in multiple spots

  • RNA primers added to many spots on this strand

  • DNA polymerase III adds Okazaki Fragments (small sections of DNA) one at a time

Additional Enzymes for Lagging Strand

To clean up the lagging strand:

1. Exonuclease: removes RNA primers

2. DNA polymerase I adds nucleotides to areas that had RNA primers

3. Then DNA ligase joins Okazaki fragments

Complementary Sequences

• If the original strand of DNA had the following sequence:

A T T C G C A G

• The newly synthesized / complementary strand after replication will have the following sequence:

T A A G C G T C

• The two resulting DNA molecules will be identical to the original molecule

Telomeres

• Telomeres: ends of eukaryotic chromosomes (think like tip of shoelace!)

• Telomerase helps add short DNA sequences to these telomeres in replication to minimize the ends being damaged or lost during replication

Replication in Living Things

• In prokaryotic organisms, their circular chromosomes are replicated by starting at a single point and then moving in both directions

• Eukaryotic chromosomes are much more complex!

• In eukaryotic cells, replication begins at multiple spots along the DNA at replication forks (could be hundreds!)

  • Replication then begins in both directions until the chromosome is copied