Nucleotides and nucleic acids Module 2

Question 1

What’s a nucleotide made up of?

Answer 1

A pentose sugar (5 carbon atoms)
A nitrogenous base
A phosphate group

Question 2

What elements do all nucleotides contain?

Answer 2

C, H O, N P

Question 3

DNA and RNA are both types of?

Answer 3

Nucleic acid

Question 4

What are the monomers of RNA and DNA?

Answer 4

Nucleotides

Question 5

General purpose of DNA?

Answer 5

To store genetic information

Question 6

General purpose of RNA?

Answer 6

To make proteins from the instructions in DNA

Question 7

ADP and ATP are types of? and their function is?

Answer 7

Phosphorylated nucleotide

Store and transport energy in cells

Question 8

What’s the pentose sugar in DNA called?

Answer 8

Deoxyribose

Question 9

What are the 4 possible bases in DNA?

Answer 9

Adenine, thymine, cytosine, and guanine

Question 10

Which are the purine bases and what does this mean?

Answer 10

Adenine and Guanine, contain 2 carbon - nitrogen rings joined together

Question 11

Which are the pyrimidine bases and what does this mean?

Answer 11

Cytosine, and thymine, only contain 1 carbon-nitrogen ring, so are smaller than a purine base

Question 12

How many polynucleotide chains does a molecule of DNA contain?

Answer 12

2

Question 13

What’s the sugar in RNA called?

Answer 13

Ribose sugar

Question 14

What does uracil (a pyrimidine) replace in RNA?

Answer 14

Thymine

Question 15

How many polynucleotide chains make up RNA?

Answer 15

1

Question 16

Structure of ADP?

Answer 16

Contains the base adenine, the sugar ribose and 2 phosphate groups

Question 17

Structure of ATP?

Answer 17

Contains the base adenine, the sugar ribose, and 3 phosphate groups

Question 18

Describe how ATP and ADP provide energy for a cell?

Answer 18

ATP provides energy for chemical reactions in a cell

It is synthesised from ADP and inorganic Pi, using the energy from an energy releasing reaction such as breakdown of glucose in respiration

So the ADP is phophorylated to from ATP and a phosphate bond is formed

Energy is stored in the phosphate bond, when the energy is needed by the cell, ATP is broken back down into ADP and Pi, and energy is released from the phosphate bond

Question 19

What do nucleotides join together to form and what between?

Answer 19

Polynucleotides, phophodiester bond forms between the phosphate group of one nucleotide, and the sugar of another forming a sugar phosphate backbone

Question 20

Describe how 2 polynucleotide strands join together to form a helix?

Answer 20

There’s hydrogen bonding between the bases
Complementary base pairing, A-T, C-G
2 Hydrogen bonds form between A-T
3 Hydrogen bonds form between C-G

The 2 antiparallel strands twist to form the DNA doubel helix

Question 21

How can you purify DNA?

Answer 21

Via a precipitation reaction

Break up cells of sample using a blender

Make a solution of detergent, salt and distilled water

Add the broken up cells to a beaker containing the solution and heat in a water bath

The detergent in the mixture breaks down the cell membranes, and the salt binds to the DNA causing it to clump together, and warm temperature prevents the stops the enzymes in the cells working properly so DNA not broken down

Put beaker in a ice bath, and then filter

Transfer to a testube and protease enzymes to the filterered mixtures, which will break down any proteins

Dribble cold ethanol down side of tube so it forms a layer on top, causing DNA to form a white precipitate

Question 22

Describe the process of DNA self replicating?

Answer 22

DNA helicase breaks down the hydrogen bonds between the 2 polynucleotide DNA strands, the helix unzips to form 2 separate strands

Each original strand acts as a template for a new strand, free floating DNA nucleotide bases join to the exposed bases on each original template strand by complementary base pairing

The nucleotides of the new strand are joined together by the enzyme DNA polymerase, this forms the sugar phosphate backbone,

Hydrogen bonds form between the bases on the original and new strand, the strands twist to form a double helix

Each new DNA molecule contains one strand from the original DNA molecule and one from new strand

Question 23

Why is DNA self replication known as semi conservative?

Answer 23

Because half the strands are from the original DNA

Question 24

What is a mutation and what might it cause?

Answer 24

Any change to the DNA base sequence, so may alter the sequence of amino acids a protein and therefore possibly form an abnormal protein

Question 25

Why does DNA replication have to be very accurate?

Answer 25

So all the genetic information is conserved

Question 26

What’s a gene?

Answer 26

A sequence of DNA nucleotides that codes for a polypeptide

Question 27

The sequence of amino acids in a polypeptide forms the?

Answer 27

Primary structure of a protein

Question 28

What determines the order of amino acids in a protein?

Answer 28

The order of nucleotide bases in a gene

Question 29

Each amino acid is coded for by?

Answer 29

A sequence of 3 bases called a triplet in a gene

Question 30

What is DNA copied in to and why for protein synthesis?

Answer 30

RNA

DNA molecules are found in the nucleus of the cell, but the ribosomes that make proteins are found outside the cell in the cytoplasm

DNA is too large to be moved out of the nucleus, so a section is copied into mRNA = transcription

So the mRNA leaves the nucleus and joins with a ribsome in the cytoplasm, where it can be used to synthesise a protein = translation

Question 31

What are the 3 main types of RNA?

Answer 31

Messenger RNA - mRNA
Transfer RNA - tRNA
Ribosomal RNA - rRNA

Question 32

Features of mRNA?

Answer 32

Made in the nucleus

3 adjacent bases are called a codon

It carries the genetic code from the DNA in the nucleus to the cytoplasm, where it’s used to make protein during translation

Question 33

Features of tRNA?

Answer 33

Found in the cytoplasm

It has amino acid binding site at one end, and a sequence of 3 bases called an anticodon

It carries the amino acids that are used to make proteins to the ribosome during translation

Question 34

Features of rRNA?

Answer 34

Forms the 2 subunits in a ribosome

The ribosome moves along the mRNA strand during protein synthesis, the rRNA in the ribosome helps to catalyse the formation of peptide bonds between the amino acids

Question 35

What’s the genetic code?

Answer 35

The sequence of base triplets (codons) in DNA or mRNA, which codes for specific amino acids

It’s non overlapping - read only in triplets

Degenerate - some amino acids are coded for by more than one base triplet

Universal - codes for same amino acids in all living thinfs

Question 36

What are found at the beginning and end of gene to tell when to stop or start gene production?

Answer 36

Start/stop codons

Question 37

Describe the first stage of protein synthesis - transcription?

Answer 37

RNA polymerase attaches to the DNA at the beginning of a gene

The hydrogen bonds break between the 2 DNA strands break, separating the strands, and the DNA molecule uncoils at that point

One of the strands is then used as a template to make an mRNA copy

The RNA polymerase lines up free RNA nucleotides alongside the template strand, complementary base pairing means that the mRNA strand ends up being a complementary copy of the DNA strand (except T is replaced by U)

Once the RNA nucleotides have paired up with their specific bases on the DNA strand they are joined together to form an mRNA molecule

The RNA polymerase moves along the DNA, separating the strands, and assembling the mRNA strand

The hydrogen bonds reform between the uncoiled strands of DNA and coil back into a double helix once the RNA polmerase passes by

When RNA polymerase reaches a stop codon, it stops making mRNA and detaches from the DNA

The mRNA moves out of the nucleus through a nuclear pore, and attaches to a ribosome in the cytoplasm

Question 38

Describe how the second step of protein synthesis occurs Translation?

Answer 38

The mRNA attaches itself to a ribosome and tRNA molecules carry amino acids to the ribosome

A tRNA molecule with it’s anticodon that’s complementary to the start codon on the mRNA attaches itself to the mRNA via complementary base pairing

A second tRNA molecule attaches to itself to the next codon in the same way

rRNA in the ribosomes catalyses the formation of a peptide bond between the 2 amino acids attached to the tRNA, this joins them together and the first tRNA molecule moves away

Process repeats untill a polypeptide chain is formed and the stop codon is reached

Question 39

Order of protein synthesis?

Answer 39

Transcription then translation