Nucleic Acids

Question 1

What is a nucleotide?

Answer 1

A phosphate ester of a pentose sugar containing

• 5 carbon sugar
• phosphate group
• nitrogenous base

Question 2

What is the pentose sugar in DNA and RNA?

Answer 2

DNA= deoxyribose
RNA= ribose

Question 3

How are the phosphate and the pentose sugar joined?

Answer 3

By a phosphoester bond

Question 4

What are some 3 roles of nucleotides?

Answer 4

Roles of nucleotide:

• monomers of nucleic acids
• help regulate metabolic pathways
• components of co enzymes

Question 5

What are the structures of Adenosine, AMP, ADP and ATP?

Answer 5

• Adenosine = adenine +ribose
• AMP (mono phosphate) = adenine + ribose +1 phosphate
• ADP (diphosphate) = adenine +ribose +2 phosphate
• ATP (triphosphate) = adenine+ribose + 3 phosphate

Question 6

Discuss the double helix structure of DNA

Answer 6

DNA

• 2 polynucleotide strands that run antiparalell
• strands run from 5’ to 3’

Question 7

What are the complimentary base pairs?

Answer 7

Complimentary base pairs are Adenine to Thymine and Guanine to Cytosine (always a purine to a pyrimidine)

Question 8

Which nitrogenous bases are a) pyrimidine b) purine

Answer 8

Pyrimidine = Cytosine and thymine
Purine = guanine and adenine

Question 9

What bond joins phosphates to pentose to deoxyribose in a DNA strand?

Answer 9

Phosphodiester bond (each phosphate has two bonds)

Question 10

How many hydrogen bonds to each base pairing form?

Answer 10

A---T = 2 hydrogen bonds
C---G = 3 hydrogen bonds

Question 11

Where is DNA found in comparison to RNA?

Answer 11

DNA is found in the nucleus while RNA is found in the nucleus and the cytoplasm

Question 12

Discuss differences between DNA and RNA

Answer 12

DNA = deoxyribose, thymine, found in nucleus
RNA= ribose, uracil, found in nucleus and cytoplasm and is shorter than DNA

Question 13

Is DNA a macromolecule or a polymer?

Answer 13

DNA is both a MACROMOLECULE and a POLYMER

Question 14

How is DNA organised in eukaryotic cells?

Answer 14

Eukaryotic Cells:

• DNA molecule wound around a HISTONE PROTEIN. this is a NUCLEOSOME
• CHROMATIN is the term for DNA packaged with histone proteins
• naked loop in mitochondria and chloroplasts

Question 15

How is DNA organised in prokaryotic cells?

Answer 15

Prokaryotic cells:

-Loop of naked DNA (no histone proteins)

Question 16

How do you purify DNA?

Answer 16

Purification by precipitation:

1. Vile of DNA in solution
2. Add SALT and ETHANOL
3. CENTRIFUGE forces solid to the bottom
4. Left with a PELLET of solid containing the DNA

Question 17

What is a genome?

Answer 17

A genome is all the DNA a cell contains

Question 18

What phase of the cell cycle is DNA replicated?

Answer 18

DNA is replicated in the S phase of interphase. The DNA in mitochondria and chloroplasts is replicated in G2 phase of interphase.

Question 19

Describe the first big step of DNA replication

Answer 19

DNA replication:

1. Double helix is unwound by gyrase
2. Strands unzipped by DNA helicase

Question 20

Describe the second big step of DNA replication

Answer 20

Synthesis of new strand:

1. free activated nucelotides align and hydrogen bond
2. DNA polymerase catalyses addition of bases in the 5’ to 3’ direction
3. Leading strand is synthesised continuously and lagging strand is synthesised discontinuously in fragments
4. fragements of lagging strand are joined by ligase enzymes

Question 21

Give the role of 4 enzymes involved in DNA replication

Answer 21

• Gyrase- unwinds double helix
• Helicase- Unzips the strands by breaking H bonds
• DNA polymerase- catalyses the addition of new bases in 5’ 3’ direction
• Ligase- joins fragments of the lagging strand
• Hydrolysis of activated nucleotides supplies the energy to make phosphodiester bonds

Question 22

Why is DNA replication semiconservative?

Answer 22

Semi conservative replication because each new DNA molecule consists of one parental strand and one daughter strand

Question 23

How is DNA replication different in prokaryotes? Does this happen at all in eukaryotes?

Answer 23

Prokaryotes DNA is a loop so a BUBBLE SPROUTS from the loop and unwind and unzips and thrn complimentary nucleotides join to exposed nucleotides. REPLICATION BUBBLE. This also occursin MITOCHONDRIA and CHLOROPLASTS

Question 24

If in prokaryotes, mitochondria and chloroplasts there is a replication bubble, what is this referred to as in eukaryotes?

Answer 24

Eukaryotes = replication fork

Question 25

how often do mutations occur during DNA replication?

Answer 25

1 in 10 to the power of 8

Question 26

Are mutations always harmful?

Answer 26

Mutations aren't always harmful, they account for the existent of alleles.

Question 27

What is a proteome?

Answer 27

Proteome = all the proteins in a cell

Question 28

What is a codon?

Answer 28

Codon = base triplet, each triplet codes for an amino acid on a length of mRNA

Question 29

What are the 3 features of genetic code?

Answer 29

- Near universal = same triplet codes for the same amino acid in most organisms - Degenerate = more than one triplet code coding for the same amino acid - Non overlapping = sequence is read from a fixed point so any insertion or deletion causes a frame shift

Question 30

How is DNA made into RNA? How then is RNA made into a protein?

Answer 30

DNA ------- RNA ----------protein | 1) transcription 2) translation

Question 31

Describe the steps of transcription

Answer 31

Transcription: 1. gene unwinds and unzips 2. RNA Polymerase catalyses temporary bonding betwen RNA nucleotides and DNA bases 3. template strand + MRNA made (coding strand) 4. mRNA passes out of nucleus through the nuclear envelope and attaches to a ribosome

Question 32

What bases does mRNA have? Why?

Answer 32

A U G C because it attaches to the bases on the template strand which have regular bases

Question 33

What bases does the template strand have?

Answer 33

A T C G

Question 34

How are ribosomes made?

Answer 34

- Ribosomes are made in the NUCLEOLUS by EQUAL PARTS rRNA and PROTEIN. - two small SUB UNITS pass out of the nucleolus and join together with the help of a MAGNESIUM ION to from a ribosome

Question 35

What is the structure of tRNA?

Answer 35

tRNA is made in the NUCLEOLUS and is a SINGLE stranded polynucleotide. They twist into the hairpin shape. one end is an ANTICODON and the other is a TRIO OF UNPAIRED BASES that bind to an amino acid.

Question 36

What are the steps of translation?

Answer 36

Translation: 1. tRNA brings an amino acid and finds where their anti codon can temporarily hydrogen bond to the mRNA codon 2. ribosome moves along the mRNA, reads, and peptide bonds form whenever two amino acids are adjacent to each other ( ATP needed) 3. Ribosome stops when it reaches a stop codon

Question 37

What happens to the mRNA after translation?

Answer 37

mRNA breaks down (gets degraded). Its components recycled

Question 38

What happens to the new polypeptide after translation?

Answer 38

The new polypeptide is helped by CHAPERONE PROTEINS to fold correctly into its 3D shape.

Question 39

What is the structure od ATP?

Answer 39

3 phosphate + ribose + adenosine

Question 40

Where is carbon 5 found?

Answer 40

Carbon 5 is found embedded in the bond between the phosphate and ribose

Question 41

How does ATP release energy?

Answer 41

Hydrolysis of ATP releases energy

Question 42

What charge are the phosphates and what does this mean?

Answer 42

The phosphates are negatively charged so they repel each other. This means the bonds are unstable so they have a low activation energy so are easily broken

Question 43

What is the equation for hydrolysis and condensation of ATP?

Answer 43

``` ATP + H2O ==== ADP + Pi (+energy) ATP hydrolase (hydrolysis of ATP) ATP synthase (synthesis of ATP) ```

Question 44

What kind of turnover does ATP have ans what does this mean?

Answer 44

ATP has a high turnover rate meaning it is a short term energy molecule due to unstable bonds

Question 45

Give examples of processes that require ATP

Answer 45

ATP is used in muscle contraction, active transport and creation of lysosomes

Question 46

How can ATP activate other molecules?

Answer 46

Hydrolyse ATP to release a Pi which binds to the molecule making it less stable, therefore more reactive

Question 47

Where are some processes where ATP is made?

Answer 47

ATP is made in photo-phosphorylation, oxidative phosphorylation and substrate level phosphorylation