nucleic acids

Question 1

where is DNA contained in prokaryotic cells

Answer 1

• in the nucleoid
• also have small circular DNA molecules called PLASMIDS

~ plasmids carry one or two genes; can replicate independently of the core genome and can be transferred from one cell to another (ex. antibiotic resistance)

Question 2

what are chromosomes

Answer 2

the organization of a double stranded DNA molecule in its association with proteins and RNAs

Question 3

why are prokaryotic chromosomes coiled up and circular?

Answer 3

• allows a bacterial chromosome (which may be longer) to fold up within the nucleoid
• small circular plasmids carry a limited number of genes required for survival in distinct environments (ex. the presence of certain antibiotics)
• preserves double helix structure and compacts DNA into a small space

Question 4

what are benign strains

Answer 4

harmless and not associated with any disease symptoms

Question 5

what are virulence strains

Answer 5

harmful; associated with symptoms such as sore throat, strep throat, pneumonia

Question 6

what is the Fred Neufeld Experiment

Answer 6

• there are two strains of the bacteria streptococcus pneumonia
• One strain, when injected into a mouse, caused death; the other strain, when injected, had no effect
• The R Strain is a harmless or benign member of the microbiome (mouse); the S Strain is a virulent form of the same bacteria

Question 7

what is the Griffith Experiment

Answer 7

• he heated the virulent bacteria to high temperatures in order to kill them
• The dead S-strain (the heated one) was injected into a mouse, and the mouse survived
• set up an experiment with 3 controls; He incubated the remains of the killed cells from the virulent strain with living cells from the benign strain and injected the combination into the mouse
  ~ he found that the mouse died, indicating that the benign bacterial cells were now virulent
  ~ concluded that the cells of the benign strand had acquired info to be virulent from dead cell

Question 8

what is transformation

Answer 8

a change in cell behaviour resulting from the incorporation of genetic material from outside of the cell

Question 9

what did oswald avery and his colleagues discover

Answer 9

• wanted to find out which macromolecule allowed for the transformation of cells
• selectively eliminated each of the macromolecules from cell extracts and then tested the remaining molecule for their ability to induce transformation
• the control: virulent heat killed bacterial extracts are incubated with the non virulent bacteria with the expectation that transformation should occur
• Researchers discovered that in the absence of protein and RNA, but in the presence of DNA, transformation occurs –> in the absence of DNA, there was no transformation

Question 10

what evidence did oswald avery and his colleagues find?

Answer 10

• in each tube, enzyme would destroy one type of macromolecule
• in all macromolecules, all mice died and they collected S-strain bacteria EXCEPT in the tube where DNA was destroyed
• all other macromolecules tell us that they do not transform those R-strain bacteria so they can’t be hereditary material

Question 11

what did rosalind franklin discover

Answer 11

• She used a technique called X-ray diffraction to aim X-rays at DNA to create images based on the diffraction of the X-rays by the atoms in the DNA molecule
• “photo 51” identified the helical structure of DNA

Question 12

what are the basic subunits of the DNA molecule

Answer 12

nucleotides

Question 13

what makes up a nucleotide

Answer 13

phosphate group, 5 carbon deoxyribose sugar, and a nitrogenous base

• phosphate group and sugar are constant; nitrogenous base changes depending on the molecule

Question 14

what are pyrimidines

Answer 14

• cytosine and thymine
• aromatic heterocyclic molecules that have a single ring

Question 15

what are purines

Answer 15

• adenine and guanine
• consist of two rings –> a pyrimidine ring fused to an amidazole ring (larger than pyrimidines)

Question 16

how is a DNA molecule assembled?

Answer 16

• a condensation rxn releases a water molecule and forms a covalent bond called phosphodiester bond between two nucleotides
• nucleotides are linked on backbone
• phosphate on the 5’ carbon of deoxyribose forms a bond with the hydroxyl group on the 3’ carbon on the next deoxyribose
• resulting DNA strand = sugar phosphate backbone with nitrogenous bases extending out

Question 17

what is chargaffs rule

Answer 17

• DNA molecules should have a one-to-one ratio of pyrimidine and purine bases
• adenine = thymine, guanine = cytosine
• Suggests that there is molecular pairing between pyrimidines and purines in the formation of DNA

Question 18

how many hydrogen bonds between thymine & adenine vs guanine & cytosine

Answer 18

• A & T : two hydrogen bonds
• G & C : three hydrogen bonds

Question 19

what did Watson and Crick determine

Answer 19

• double helix structure of DNA
• the two strands of DNA run antiparallel to each other, with the bases facing inwards (diameter = 2 nm)
• helix has a major groove and minor groove with one churn of the helix occurring every 10 nucleotides

Question 20

what are the two biochemical differences between DNA & RNA

Answer 20

1) the 5 carbon sugar in RNA is ribose instead of deoxyribose

• ribose has a OH group on the 2’ carbon while deoxyribose has a H at 2’ C

2) in RNA, the pyrimidine uracil replaces thymine and binds with adenine

• uracil has a H where thymine has a methyl group

Question 21

how are phosphodiester bonds formed in RNA

Answer 21

The three prime hydroxyl/three prime end of the existing polymer attacks the high energy phosphate bond of the new ribonucleotide

Question 22

what is messenger RNA

Answer 22

the RNA copy of genes that codes for proteins

• single stranded molecules that can be translated into proteins by ribosomes

Question 23

what is transfer RNA

Answer 23

• a functional RNA; never translated
• sequence of the RNA is such that it folds into a 3-D structure held together by base pairing between ribonucleotides
• attaches to amino acids and brings them to ribosomes during translation
• match the amino acid to the appropriate mRNA sequence

Question 24

what is ribosomal RNA

Answer 24

• a functional RNA
• transcribed from ribosomal genes of which there are many copies in the cell & its a very large proportion of the total RNA in a cell
• Three different ribosomal RNAs molecules that together form integral components of the ribosome

Question 25

what is the organization of DNA molecules in the nucleus

Answer 25

are linear molecules that are organized around proteins called histones to form chromatin

Question 26

how does the measurement of DNA change

Answer 26

- is 2 nm in width, but when folded around histones, it forms a fiber that is 10 nm wide - further coiling creates a 30 nm chromatin fiber - additional coiling creates metaphase chromosome - compacted chromosome can move more easily during cell division

Question 27

what are some differences between prokaryotes and eukaryotes (based on DNA)

Answer 27

- size of eukaryotic chromosome is greater than bacterial nucleoid - eukaryotic genome is bigger than prokaryotic genome - prokaryotes have abt 4290 protein coding genes; eukaryotes have 20,000

Question 28

what are some similarities between prokaryotes and eukaryotes

Answer 28

- same double helix - same nucleotides - similar genes coding for proteins (ex. those of RNA polymerases and ribosomes)

Question 29

how to tell if an amino acid is non-polar/hydrophobic

Answer 29

- R group looks like a hydrocarbon (CH2, CH3) bound together like a fatty acid tail - anything with benzene is mostly hydrophobic

Question 30

how to tell if an amino acid is polar/hydrophilic

Answer 30

- R group is basic or acidic - anything charged will interact with water - hydroxyl group (make H-bonds)

Question 31

what are the special amino acids

Answer 31

- glycine --> smallest (HYDROPHOBIC) - proline --> R group makes covalent bond with amino group, making it bigger (HYDROPHOBIC) - cysteine --> thiol group behaves as a OH group (slightly POLAR)