Bio 3 - Genetics

Question 1

Name 4 bases of DNA

Answer 1

Cytosine
Guanine
Adenine
Thymine

Question 2

What bases bond + how many bonds

Answer 2

A=T (double)
C=-G (triple)

Question 3

Pyrimidines vs Purines
-Structure
-Bases

Answer 3

Purines: double ringed A and G
Pyrimidines: single ringed CUT

Question 4

What carbon is attached to the:
-phosphate group
-nitrogenous base

Answer 4

Carbon 5 - ester bond (phosphodiester)
Carbon 1 - glycosyl bond

Question 5

What is attached by glycosyl bonds

Answer 5

Sugar - Base (carbon 1)

Question 6

What is attached by phosphodiester bonds

Answer 6

Phosphate group - Sugar (carbon 5, carbon 3)

Question 7

Pyrimidines vs Purines (bases and structure)

Answer 7

Pyrimidines - CUT (single ringed)
Purines - AG (double ringed)

Question 8

What is 5’ and 3’

Answer 8

5’ is at the “top” of nucleotides
3’ is at the “bottom” of nucleotides

Question 9

Bonds between bases

Answer 9

H-Bonds

Question 10

7 Historical figures in the discovery of DNA

Answer 10

Frederich
Hammerling
Griffith
Hershey/Chase
Chargaff
Rosalind/Wilkins
Watson/Crick

Question 11

Frederich

Answer 11

Puss guy, discovered nuclein and that the hereditary information is stored within

Question 12

Hammerling

Answer 12

Algae cap chopping, discovered the location of hereditary information

Question 13

Griffith

Answer 13

Pneumonia and mice, disocvered that DNA is the transforming principle

Question 14

Hershey/Chase

Answer 14

Bacteriophage injects hereditary material (DNA not protein!), discovered that DNA was reponsinsible for genetic information

Question 15

Chargaff

Answer 15

Studied nucleotide composition and found
1. Each species has unique composition of nitrogenous bases
2. Chargaff’s Rule = amount of A = T and C = G ∴ A + G = T + C Purines =
pyrimidines

Question 16

Rosalind/Wilkins

Answer 16

Used xray diffraction to analyze DNA by bombarding it with xrays which deflected atoms that produced patterns on photographic film.
1. Diffraction patterns suggested
2. DNA was the shape of double helix

Question 17

Watson/Crick

Answer 17

Used everyone else’s research to conclude the shape of DNA + 3D model

Question 18

Conservative Replication

Answer 18

One daughter molecule would be unchanged from the parent molecule and one
daughter molecule would consist of newly synthesized strands. In conservative replication,
the two parental strands would act as templates for replication, but then recombine
afterwards.

Question 19

Semiconservative Replication

Answer 19

Each daughter molecule receives one strand from the parent plus one newly
synthesized strand. In semiconservative replication, the two parental strands would act as
templates for replication and remain separated from each other, incorporated into two new
molecules

Question 20

Dispersive Replication

Answer 20

The new strands of DNA are a mix of both paternal and daughter DNA

Question 21

3 Steps of DNA replication

Answer 21

Initiation, elongation, termination

Question 22

What happens during DNA initiation + 3 enzymes

Answer 22

2 strands of double helix separated by DNA helicase enzyme that breaks hydrogen bonds; where hydrogen bonds break is replication fork

Single-stranded binding proteins (SSBs) replication enzyme that prevents parent DNA strands from annealing to each other once they have been separated by helicase

Gyrase enzyme (also known as topoisomerase) enzymes that relieve tension caused by the unwinding of parent DNA; they cleave one or two of the DNA strands, allow the strand(s) to untwist, and then rejoin the strand(s)

Question 23

What happens during DNA elongation

Answer 23

DNA polymerase III brings free nucleotides into the replicating fork, it moves from 5’ to 3’ looking for the 3’ end. It then adds nucleotides using RNA primers

The lagging chain is built in the opposite direction and built in sections. (3’-5’-3’). Primers are added and DNA polymerase III builds in short fragments called Okazaki fragments.

DNA polymerase I replaces RNA primers with correct nucleotides .
DNA ligase joins Okazaki fragments by phosphodiester bond.

Question 24

What happens during DNA termination?

Answer 24

Once strands complete , daughter DNA rewind. DNA polymerase III and I (exonnucleases) proof read new strands and splice out any mistakes and replace the correct nucleotide.

Question 25

3 Steps of transcription

Answer 25

Initiation, Elongation, Termination

Question 26

What happens during transcription initiation

Answer 26

Enzyme RNA polymerase binds to the DNA molecule upstream of the gene to be copied.
Enzyme attaches to “promoter” region on DNA that tells the polymerase where to start and which strand to copy.
The DNA region usually has a high number of A and T, which only have 2 hydrogen bonds to break. The TATA box.
The binding of polymerase opens the double helix

Question 27

What happens during transcription Elongation

Answer 27

RNA polymerase moves along the “template strand” of DNA, adding RNA nucleotides in the 5’ to 3’ direction
The strand not used for transcription is called the coding strand
Complementary mRNA strand is built with bases ACGU
As polymerase moves along, DNA rewinds back together

Question 28

What happens during termination transcription.

Answer 28

RNA polymerase moves along the gene until a “terminator sequence” is reached – sequence of bases that tells the enzyme to stop
mRNA now released from DNA is called “messenger RNA primary transcript”. RNA polymerase is also released and can be used to transcribe again
RNA polymerase does not proof read the sequence

Question 29

MRNA modification + Steps

Answer 29

After transcription in Eukaryotes, mRNA is modified before leaving the nucleus

1. Capping: The 5’ end receives a molecule of 7-methylguanosine is added at the start of the
   primary transcript. This protects mRNA and helps mRNA bind to the ribosome
2. Poly-A tail : string of 200 – 300 adenine bases added to the end of mRNA. Helps
   protect mRNA.
3. Splicing: primary transcript consists of exons and introns both copied from DNA.
   Exons = sections that code for a specific protein
   Introns = do not code for a protein and will not be expressed.
   Spliceosomes = RNA and protein act to cut out introns from primary transcript and then rejoin the remaining exons.

After capping, tailing and splicing the new “mRNA transcript” exits the nucleus

Question 30

Translation initiation

Answer 30

mRNA binds to the small subunit of the ribosome
large subunit binds to mRNA clamping mRNA in between the 2 subunits
FIRST tRNA moves into P site, interacts with mRNA bases on complementary base pairing
in eukaryotes – first tRNA binds to mRNA start codon AUG; its anticodon is UAC; it carries amino acid methionine

Question 31

Translation Elongation

Answer 31

SECOND tRNA moves into A site
2 amino acids will link by a peptide bond
First tRNA is released, ribosomes shifts down one codon, second tRNA is now in P site , A site is open
Process continues with ribosome moving along the mRNA in the 5’ to 3’ direction, reading one codon (3 nucleotides) at a time, adding one amino acid

Question 32

Translation termination

Answer 32

Ribosome eventually reaches mRNA’s “stop codon” ( UGA, UAG or UAA) and stalls
No tRNA anticodons match these codons
Proteins called release factors recognize these codons and will cause polypeptide to release from ribosomes ( protein’s primary structure)
Ribosome will break down into its 2 parts
mRNA may be reused or read again to make more copies

Question 33

Types of mutation

Answer 33

Point (silent, nonsense, missense)
Frameshift (substitution, deletion)
Chromosomal (Abnormal Structure - Deletion, Inversion, Duplication, Translocation)(Abnormal Number - Nondisjunction, Polyploids)

Question 34

Alternative Splicing

Answer 34

Process that produces different mRNAs from primary mRNA,
allowing more than 1 polypeptide to be made from 1 gene. This explains why humans can produce 100 000 proteins from only 20 000 genes.

Question 35

Prokaryotes vs Eukaryotes
Genome
Transcription
Translation

Answer 35

Prokaryotes / Eukaryotes
Genome: Small and circular, all coding but promoters&operators, operons / large chromosomes, coding and non coding, no operons
Transcription: with translation, no excision / in nucleus, splicing
Translation: formylmethoinine, ShineDalgama binding site, small ribosomes / methionine, 5’ cap binding site, cytoplasm, big ribosomes

Question 36

chromatin:

Answer 36

complex of DNA and histone proteins located in the nucleus of eukaryotes ***chromosomes only form during mitosis

Question 37

histones:

Answer 37

positively charged proteins that bind to negatively charged DNA in chromosomes

Question 38

nucleosome:

Answer 38

a complex of eight histones enveloped by coiled DNA
supercoiling: DNA folded into a higher level of coiling than is already present in nucleosomes

Question 39

variable number tandem repeats(VNTRs):

Answer 39

repetitive sequences of DNA that vary among individuals; also known as microsatellites

Question 40

telomeres:

Answer 40

long sequences of repetitive, noncoding DNA on the end of chromosomes

Question 41

centromeres:

Answer 41

constricted region of chromosome that holds two replicated chromosome strands together

Question 42

pseudogenes:

Answer 42

DNA sequences that are homologous with known genes but are never transcribed (fake genes do not code for anything; no real function)

Question 43

LINEs:

Answer 43

repeated DNA sequences of 5000 to 7000 base pairs in length that alternate with lengths of DNA sequences found in the genomes of higher organisms (types of pseudogenes)

Question 44

SINEs:

Answer 44

repeated DNA sequences of 300 base pairs in length that alternate with lengths of DNA sequences found in the genomes of higher organisms (pseudogenes)