Proteins + nucleotides+ nucleic acids- biological molecules

Question 1

Made up of (elements)

Answer 1

-carbon, hydrogen, oxygen, nitrogen

Question 2

peptides

Answer 2

polymers made up of amino acid molecules (the monomers)

Question 3

What do proteins consist of

Answer 3

• one or more polypeptides arranged as complex macromolecules
• they have specific biological functions

Question 4

essential vs non essential amino acids

Answer 4

• 20 commonly found in cells, five are non essential as our bodies are able to make them from other amino acids,
• 9 are essential and can only be obtained by what we eat
• further 6 said to be conditionally essential as they are needed for growing children

Question 5

synthesis of peptides

Answer 5

• amino acids join when the amine and carboxylic acid groups connected to central carbon atoms react
• r groups not involved yet
• the hydroxyl in carboxylic acid group of one amino acid reacts with a hydrogen in the amino group of another amino acid
• peptide bond is formed between and h2o is produced (condensation reaction)
• resulting compound is a dipeptide

Question 6

polypeptide

Answer 6

• when many amino acids are joined together by peptide bonds

- catalysed by the enzyme peptidyl transferase present in ribosomes

Question 7

primary structure- protein structure

Answer 7

• the sequence in which the amino acids are joined
• the particular amino acids in the sequence will influence how the polypeptide folds
• peptide bonds only

Question 8

secondary structure- protein structure

Answer 8

• O2, H, N atoms of amino acids interact
• hydrogen bonds may form within the amino acid chain, pulling it into a coil shape called an alpha helix
• or can form beta pleated sheets when polypeptide form hydrogen bonds lying parallel

Question 9

tertiary structure- protein structure

Answer 9

• folding of a protein into its final shape
• the coiling or folding in their secondary structures brings r groups closer together so they are able to interact and further folding will occur

Question 10

Interactions between R groups (4)

Answer 10

• hydrophobic and hydrophilic interactions (weak interactions between polar and non polar R groups)
• hydrogen bonds (weakest bonds formed)
• ionic bonds (form between oppositely charged R groups)
• disulphide bonds ( covalent and strongest of the bonds, only form between R groups that contain sulphur atoms)

Question 11

quaternary structure-protein structure

Answer 11

• results from the association of 2 or more individual proteins called subunits-
• enzymes consist of 2 identical subunits whereas insulin has 2 different subunits
• haemoglobin has 4 subunits made of 2 sets of 2 identical subunits

Question 12

hydrophilic and hydrophobic interaction affect on the way a protein will fold

Answer 12

• proteins assembled in aqueous environment of cytoplasm
• will depend on if R groups are hydrophilic or hydrophobic
• hydrophilic on outside of protein, hydrophobic on inside

Question 13

Steps of DNA replication

Answer 13

-The double helix unwinds and the hydrogen bonds between the complementary
bases break using DNA helicase thus separating the two strands of DNA
-Both strands are used as templates and
complementary base pairing occurs between the template strands and free nucleotides
-Adjacent nucleotides are joined by phosphodiester bonds formed in condensation reactions using DNA polymerase

Question 14

Twenty different amino acids are commonly used for protein synthesis. In theory, this
would need only 20 different base combinations.
Explain the uses of the remaining 44 combinations.

Answer 14

• several code for one amino acid

- some are used to stop terminations

Question 15

Which nucleotide bases are common to DNA and RNA?

Answer 15

Adenine, cytosine, guanine

Question 16

Transcription

Answer 16

During transcription, a molecule of mRNA is made in the nucleus:
• The hydrogen bonds between the complementary bases break and the DNA uncoils
thus separating the two strands
• One of the DNA strands is used as a template by RNA polymerase to make the mRNA molecule. the DNA template is called the antisense strand
• Free nucleotides line up by complementary base pairing and adjacent nucleotides are joined by phosphodiester bonds made by RNA polymerase thus forming a single stranded molecule of mRNA
• mRNA then moves out of the nucleus through a pore and attaches to a ribosome in
the cytoplasm which is the site of next stage of protein synthesis called translation

Question 17

Translation

Answer 17

During translation amino acids join together to form a polypeptide chain.
• mRNA attaches to a ribosome and transfer RNA collects amino acids from the
cytoplasm and carries them to the ribosome. tRNA is a single stranded molecule
with a binding site at one end thus it can only carry one type of amino acid, and a
triplet of bases at the other
• tRNA attaches itself to mRNA by complementary base pairing – two molecules
attach to mRNA at a time
• The amino acids attached to two tRNA molecules join by a peptide bond and then
tRNA molecules detach themselves from the amino acids, leaving them behind
• This process is repeated thus leading to the formation of a polypeptide chain until a
stop codon is reached on mRNA and ends the process of protein synthesis

Question 18

Purines vs Pyrimidine

Answer 18

• Purines, double ring structures, A+G

- Pyrimidines, single ring structures, C+T +U

Question 19

State two ways in which a diagram of part of an RNA molecule would appear different
from the DNA molecule

Answer 19

• Uracil instead of thymine

- would not have 2 strands, single stranded

Question 20

Explain why DNA replication is considered to be semi-conservative.

Answer 20

• one strand from original DNA and one strand newly formed

- original strand / polynucleotide , acts as template for new strand

Question 21

Explain why complementary base-pairing is important in DNA replication.

Answer 21

• (DNA) can be replicated without error / same sequence of nucleotides is produced ;
• reduces occurrence of mutation
• allows reformation of hydrogen bonds

Question 22

State and explain ways in which the glucose molecule is well suited to its function in
living organisms

Answer 22

-soluble so can be (easily) , transported / carried
(around organism) ;
-small (molecule) so can , be transported / diffuse ,
across (cell) membranes ;
-easily / quickly , respired / oxidised / broken down , to , release energy / produce ATP ;
-molecules can , join , to produce , (sucrose/maltose/lactose) disaccharides / (starch, cellulose, glycogen) polysaccharides

Question 23

Describe the structure of the collagen molecule.

Answer 23

peptide bonds , between amino acids / in
polypeptide ;
every 3rd amino acids is , same / glycine ;
coil / twist / spiral / helix ;
left-handed (helix) ;
glycine / small R group , allows closeness /
twisting (of polypeptide chains) ;
three polypeptide chains ;
hydrogen / H , bonds between (polypeptide)
chains ;
no / few, hydrophilic (R) groups on outside (of
molecule) ;
(adjacent molecules joined by) crosslinks ;
crosslinks / ends of molecules , being
staggered ;
fibril