Nucleotides

Question 1

Name the 4 bases found in DNA, name the bonds that form between them

Answer 1

Adenine - Thymine and Guanine -cytosine. Hydrogen bonds

Question 2

which bases are purines

Answer 2

Adenine and Guanine (think of PURE SILVER Ag)

Question 3

which bases are pyrimidines

Answer 3

Cytosise, Thymine and Uracil

Question 4

Describe the complementary base pairing rule found in DNA

Answer 4

Adenine to Thymine (2 H bonds) Cytosine to Guanine (3 H bonds). Adenine also

Question 5

Why does a purine always pair with a pyrimidine in the DNA molecule?

Answer 5

Purines are double ring structures and pyrimidines are single ring structures. The purine-pyrimidine pair ensures that the “rungs” of the DNA ladder are always the same length

Question 6

Draw a nucleotide

Answer 6

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Question 7

Draw a polynucleotide. Label the phosphodiester bond

Answer 7

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Question 8

Which molecules make up the ‘backbone’ of a polynucleotide?

Answer 8

Phosphates and pentose sugars

Question 9

Which enzyme separates the strands in DNA replication

Answer 9

DNA Helicase, by breaking hydrogen bonds between the bases

Question 10

State the role of DNA polymerase

Answer 10

Joins nucleotides together by condensation reactions that form phosphodiester bonds

Question 11

Why is DNA replication known as ‘semi conservative’?

Answer 11

Because the orginal DNA molecule is split in two and half of each new molecule comes from the original. Each new DNA molecule has consists of 1 “parent” and 1 “new” strand

Question 12

State 3 differences between RNA and DNA

Answer 12

RNA is single-stranded, has U instead of T as a base, has ribose as a sugar (not deoxyribose) and is smaller

Question 13

Describe the structure and function of tRNA

Answer 13

tRNA is a single stranded polynucleotide that coils and binds to itself to form a clover-leaf structure. It has a sequencd of 3 exposed bases called the anticodon that will bind to the mRNA codon and also contains a site for the attachment of a specific amino acid. Its function is to bring a specific amino acid to the ribosome during protein synthesis

Question 14

Describe DNA replication

Answer 14

DNA helicase breaks the hydrogen bonds, unzipping the DNA, then free nucleotides bind to the exposed bases via complementary base pairing. Then DNA polymerase makes phosphodiester bonds to join the backbone of the new strand. In reality one strand is synthesied continuosly and one is synthesied in chucks called okazaki fragments that are then joined by DNA ligase.

Question 15

What is ATP made of?

Answer 15

Adenine, ribose and three phosphates (adenione and ribose together = adenosine)

Question 16

Explain how ATP is adapted for it’s role and state one disadvantage of ATP

Answer 16

energy is released in small, manageabe amounts (compared to e.g. glucose), energy is released immediately. BUT it cannot be stored so has to be continuously produced where it is needed

Question 17

Name 5 processes that ATP is required for

Answer 17

metabolic processes (building molecules), movement, active transport, secretion of substances, activation of molecules

Question 18

Water is dipolar. What do we mean by dipolar?

Answer 18

One end of the molecule has a slight positive charge, the other end is slightly negative

Question 19

Why is water important for living things?

Answer 19

It is used in metabolism (condensation/ hydrolysis), it is a solvent for many substances, water potential has to be at the right level so cells don’t shrivel or burst due to osmosis

Question 20

How does ATP release energy to a cell?

Answer 20

ATP undergoes hydrolysis to form ADP + Pi, releasing energy. Its important to note the overall reaction releases energy not just the breaking of the phospate to

Question 21

What enzyme makes the majority of ATP in the cell. Briefly describe how it works

Answer 21

ATP synthase. This enzyme uses proton gradients across a membrane. Protons flow through the enzyme making it spin. The spinning releases ATP formed on the surface of th enzyme

Question 22

What properties of water provide stable aquativ environments?

Answer 22

High specific heat capacity provides thermally stable environments. The fact that ice has a lower density than water means that freezing bodies of water are insulated by a layer of ice forming on top (like a pond in winter)

Question 23

What properties of water are crucial for transpiration. Explain

Answer 23

cohesion - water molecules stick together. Adhesion - water molecules stick to the walls of the xylem. The cohesion tension theory explains that as water molecules evaporate from the leaves of plants the cohesion-tension created pulls on the column of water molecules below in the xylem causing transpiration.

Question 24

Draw a few molecules of water showing the bonding that you would see

Answer 24

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Question 25

what famous DNA experiment does this picture show

Answer 25

the meselson stahl experiment

Question 26

Briefly describe the meselson-stahl experiment

Answer 26

Bacteria grown on heavy N-15 so all the DNA was “heavy”. Bacteria transferred to N-14 medium and divided every 20 minutes. After 1 division all the DNA was “intermediate” and after 2 divisions 50% of the DNA was “light” and 50% “intermediate”.