C5- Molecular Biology

Question 1

What is Protein Synthesis

Answer 1

Protein synthesis is the biological process by which cells build proteins based on the instructions encoded in DNA. It occurs in two main stages: Transcription and Translation

Question 2

Enzymes

Answer 2

Are biological catalysts. Catalysts control the rate of a reaction- they speed it up or slow it down - but they are chemically unchanged at the end of the reaction.

Question 3

Enzyme Actions

Answer 3

Are specific in reaction, which means they affect only one type of reaction –> they work by providing a surface or ‘active site’ where reactions can take place.

Question 4

Substrates

Answer 4

The molecules on which an enzyme acts.

Question 5

Photosynthesis

Answer 5

is teh process in which plant cells capture energy from the sunlight and use it to combine carbon dioxide and water to make sugars and oxygen.

Question 6

Chloroplasts

Answer 6

Chloroplasts are organelles in plant cells responsible for photosynthesis. They contain chlorophyll, which absorbs sunlight to convert carbon dioxide and water into glucose and oxygen. Photosynthesis occurs in the thylakoids (light-dependent reactions) and stroma (Calvin cycle). Chloroplasts have their own DNA, allowing some independent protein production.

Question 7

Thylakoids

Answer 7

Thylakoids are disk-shaped structures inside chloroplasts where the light-dependent reactions of photosynthesis occur. They contain chlorophyll and other pigments that capture sunlight to produce ATP and NADPH. Thylakoids are stacked into grana.

Question 8

Grana

Answer 8

Grana are stacks of thylakoids inside chloroplasts where the light-dependent reactions of photosynthesis occur. They increase the surface area for capturing sunlight and producing ATP and NADPH

Question 9

Stroma

Answer 9

Stroma is the fluid-filled space inside chloroplasts that surrounds the grana. It contains enzymes, DNA, and ribosomes and is the site of the Calvin cycle (light-independent reactions), where carbon dioxide is converted into glucose using ATP and NADPH from the light-dependent reactions.

Question 10

Chlorophyll

Answer 10

Chlorophyll is the green pigment in chloroplasts that absorbs light energy for photosynthesis. It is found in the thylakoid membranes and plays a key role in converting sunlight into chemical energy.

Question 11

DNA replication

Answer 11

the process by which a cell copies its DNA before cell division ensuring that each daughter strand receives an identical set of genetic information

Question 12

Semi-conservative process

Answer 12

Each new DNA molecule consists of one original strand (template strand) and one newly synthesized strand

Question 13

Where does DNA replication occur

Answer 13

DNA replication occurs in the nucleus of eukaryotic cells and in the cytoplasm of prokaryotic cells. It takes place during the S phase of the cell cycle before cell division to ensure that each daughter cell receives an identical copy of the DNA.

Question 14

Step 1 in DNA replication

Answer 14

Initiation – The enzyme helicase unwinds the DNA double helix, breaking the hydrogen bonds between complementary base pairs, creating a replication fork. single strand binding proteins (SSB’s) stabilise the unwound strand and prevent them from reannealing

Question 15

Step 2 in DNA replication

Answer 15

Priming – RNA primase synthesizes a short RNA primer on each DNA strand to provide a starting point for DNA polymerase (III).

Question 16

Step 3 in DNA replication

Answer 16

Elongation –

On the leading strand, DNA polymerase continuously adds nucleotides in the 5’ to 3’ direction, following the unwinding of the helix.
On the lagging strand, DNA polymerase adds nucleotides in fragments called Okazaki fragments, which are later joined by DNA ligase.

Question 17

Step 4 in DNA replication

Answer 17

Termination – DNA polymerase (I) replaces RNA primers with DNA nucleotides to complete the new strands. Gaps between Okazaki fragments are sealed by DNA ligase, resulting in two continuous and complete DNA molecules

Question 18

Genome sequencing

Answer 18

Genome sequencing determines an organism’s complete DNA sequence, including genes and non-coding regions. It involves extracting, fragmenting, sequencing, and assembling DNA using next-generation sequencing (NGS).

Question 19

Exonuclease

Answer 19

An exonuclease is an enzyme that removes nucleotides from the ends of a DNA or RNA strand, including the removal of RNA primers during DNA replication, to allow for proper DNA synthesis.

Question 20

DNA Ligase

Answer 20

DNA ligase is an enzyme thatfacilitates the joinging of DNA strands by catlalysing the formation of a phosphodiester bond between 3’-hydroxl end of one DNA strand and the 5’-phosphorate end of another.

Sealing the gaps between Okazaki fragments on the lagging strand

Question 21

DNA polymerase

Answer 21

DNA polymerase is an enzyme that synthesizes new DNA strands by adding nucleotides to a pre-existing strand during DNA replication. It works in the 5’ to 3’ direction, using a template strand to match complementary bases (A-T, C-G). DNA polymerase also has proofreading capabilities to correct errors during replication, ensuring accurate DNA duplication.

Question 22

DNA Primase

Answer 22

Primase is an enzyme that synthesizes a short RNA primer during DNA replication. The primer provides a starting point for DNA polymerase to begin adding nucleotides, as DNA polymerase can only extend an existing strand and cannot start from scratch.

Question 23

Catabolism

Answer 23

Substrates are broken down

Question 24

Anabolism

Answer 24

Substrates are built up

Question 25

The Mitochondria

Answer 25

Mitochondria are membrane-bound organelles found in eukaryotic cells (animals, plants, fungi). Known as the powerhouses of the cell, they generate energy in the form of ATP through AEROBIC cellular respiration.

Question 26

Mitochondria Location

Answer 26

Found in the cytoplasm of most eukaryotic cells- they are absent from red blood cells

Question 27

Mitochondria Function

Answer 27

Creates adenosine triphosphate through oxidative phosphororlyation (OXPHOS) ATP is a chemical energy source.

Question 28

Mitochondria Structure

Answer 28

Mitochondria are double-membrane-bound organelles with an outer membrane, an inner membrane (folded into cristae), an intermembrane space, and a matrix.

Question 29

Glycolysis

Answer 29

Glycolysis is the first step of cellular respiration, where glucose (6c) is broken down into 2 pyruvates (3c), producing 2 ATP and 2 NADH. It occurs in the cytoplasm and does not require oxygen (anaerobic process). Glycolysis provides energy for the cell and supplies intermediates for other metabolic pathways.

Question 30

Link Reaction

Answer 30

The link reaction (also called the pyruvate oxidation step) connects glycolysis to the Krebs cycle in cellular respiration. It occurs in the mitochondrial matrix, where pyruvate (from glycolysis) is converted into acetyl-CoA, releasing carbon dioxide (CO₂) and producing NADH.

Question 31

Kreb Cycle

Answer 31

The Krebs cycle (also called the citric acid cycle) occurs in the mitochondrial matrix and generates energy through a series of reactions. The major steps are: Acetyl-CoA joins oxaloacetate → Forms citrate. Citrate is converted → Releases CO₂ and produces NADH. More CO₂ is released → Another NADH is generated. ATP (or GTP) is produced. FADH₂ and NADH are formed as electrons are transferred. Oxaloacetate is regenerated, allowing the cycle to repeat. This process produces NADH and FADH₂, which carry electrons to the electron transport chain for ATP production.

Question 32

Electron Transport Chain

Answer 32

The electron transport chain (ETC) in the inner mitochondrial membrane uses electrons from NADH and FADH₂ to pump H⁺ ions, creating a gradient. Oxygen forms water, and ATP synthase generates about 34 ATP, making it the most efficient energy-producing stage.

Question 33

Globular Protein Function

Answer 33

Globular proteins have diverse roles, including: Enzymes (e.g., amylase) – Speed up reactions. Hormones (e.g., insulin) – Regulate body functions. Transport proteins (e.g., hemoglobin) – Carry oxygen. Antibodies – Defend against pathogens.

Question 34

Globular Protein Structure

Answer 34

Globular proteins are made up of compactly folded polypeptide chains They are stabilized by polar and nonpolar interactions Hydrophobic amino acid side chains are buried in the interior of the protein Hydrophilic amino acid side chains are exposed on the surface of the protein

Question 35

polypeptide?

Answer 35

A polypeptide is a chain of amino acids that are linked together by peptide bonds.

Question 36

Active site

Answer 36

The active site of an enzyme is the region where substrate molecules bind and undergo a chemical reaction. It's a vital part of the enzyme, responsible for catalysing the reaction.

Question 37

Light Dependent:

Answer 37

the chlorophyll in the thylakoid membrane absorbs solar energy and uses this energy to split the water molecule into hydrogen and oxygen. The oxygen is released from the chloroplast and the hydrogen is carried by NADP to the stroma

Question 38

Light independent:

Answer 38

this occurs in the liquid space of teh chloroplast or stroma. CO2 and hydrogen enter a biochemical cycle which uses ATP from the light dependent phase

Question 39

Proteins

Answer 39

Are the most abundant organic molecules in cells, and they are needed by the body for growth and repair.

Question 40

Protein strucutre

Answer 40

They are large molecules made up of amller molecules called amino acids, joined together by peptide bonds to form a polypeptide chain

Question 41

Triplets

Answer 41

a sequence of 3 nitrogenous bases [A,T,C,G] is called a triplet- each triplet provides the genetic instructions for a correspnding amino acid.

Question 42

Codon

Answer 42

When DNAis transcribed into mRNA teh triplets are converted into codons. A codon is a 3 base sequence in mRNA (using uracil) that directs teh addition of a specific amino acid during translation)

Question 43

mRNA

Answer 43

is a single stranded molecule that carries the transcribed genetic code from the DNA to the ribosomes in the cytoplasm it contains codon- groups of 3 nucleotide bases- each specifically a particular amino acid or a stop signal for translation

Question 44

tRNA

Answer 44

tRNA deliver specific amino acids to teh ribosomes based on teh codons in the mRNA, each tRNA has: → A clover leaf structure →AN anti-codon: complementary to a codon on the mRNA →A binding site for a specific amino acid, ensuring precise pairing

Question 45

Ribosomes

Answer 45

Are molecular machines composed of rRNA and proteins. They consist of two sub-units (large and small) and act as teh site for translation. Ribosomes: → Bind the mRNA strand →Align tRNA molecules carrying amino acids →Catalyse the formation of peptide bonds between amino acids, building the polypeptide chain.

Question 46

Translation

Question 46

Transcription

Answer 46

→DNA unwinds in teh nucleus at prompte region →RNA polymerase sythesis mRNA from teplate srand →Process starts at start codon

Question 47

Lac Operon

Answer 47

The lac operon is a gene regulation system in E. coli that controls lactose metabolism. When lactose is absent, a repressor protein blocks transcription, but when lactose is present, it binds to the repressor, allowing the genes to be transcribed. If glucose is available, the operon remains off to prioritize glucose usage.

Question 48

Catabolic reactions:

Answer 48

break down substances and release energy (exergonic). e.g cellular respiration

Question 49

Anabolic reactions:

Answer 49

Build up substances and consume energy→ Endergonic reactions. Build larger , more complexmolecules from smaller ones, build up or sythesis.

Question 50

Inhibitors

Answer 50

Are molecules that interact in some way with the enzyme to prevent it from working in the normal manner.

Question 51

Inhibitors effects

Answer 51

→ change the shape of the enzyme and make it unusable to a substrate →inhibitors can also act as a substrate and bind to the active site of the enzyme

Question 52

Competitive Inhibitors

Answer 52

Competitive inhibitors are molecules that bind to the active site of an enzyme, preventing the substrate from attaching and slowing down the reaction. They compete with the substrate but can be overcome by increasing the substrate concentration.

Question 53

Non-competitive Inhibitors

Answer 53

Non-competitive inhibitors bind to an enzyme's allosteric site (not the active site), changing the enzyme's shape so the substrate can no longer bind effectively. Increasing substrate concentration does not overcome this inhibition. → used during respiration →stored as insoluble starch →used to make other organic chemicals that organisms need

Question 54

Anaerobic respiration

Answer 54

A type of respiration that occurs without oxygen, where glucose is partially broken down to release energy. It produces less ATP than aerobic respiration and creates byproducts like lactic acid (in animals) or ethanol and carbon dioxide (in yeast and plants).

Question 55

Aerobic respiration

Answer 55

A process in which cells break down glucose using oxygen to produce energy (ATP), carbon dioxide, and water. It occurs in the mitochondria and is the main way organisms generate energy efficiently.

Question 56

DNA qualities

Answer 56

Genetic material found in all living organisms Stores instructions for growth, development, and function Made of nucleotides (A, T, C, G) arranged in a sequence Double helix structure (two strands twisted together) Found in the nucleus of cells (or cytoplasm in some organisms) Codes for proteins that determine traits and functions

Question 57

Splicing

Answer 57

A process in gene expression where introns (non-coding regions) are removed from pre-mRNA, and exons (coding regions) are joined together to form mature mRNA. This allows the correct genetic instructions to be translated into proteins.