Chapter 4

Question 1

Define protein

Answer 1

A type of biomacromolecule made of amino acid chains folded into a 3D shape

Question 2

Define peptide

Answer 2

a short chain of amino acids

Question 3

Define polypeptide

Answer 3

A long chain of amino acids. Proteins can be made of 1, or many polypeptides

Question 4

Define proteome

Answer 4

All the proteins that are expressed by a cell or organism

Question 5

Define enzyme

Answer 5

An organic molecule, typically a protein, that catalyses ( speeds up) specific reactions

Question 6

Define receptor protein

Answer 6

A protein within, or on the surface of cells that binds with signalling molecules, leading to a change in cellular activity

Question 7

Define peptide hormone

Answer 7

A protein signalling molecule that regulates physiology or behaviour, including growth, appetite and energy metabolism, cardiac function, stress, and reproductive physiology.

Question 8

Define structural protein

Answer 8

A type of protein that confers trength and structure to cells, E.G collagen, keratin, Elastin, Actin

Question 9

Define antibody

Answer 9

An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the pathogen, called an antigen.

Question 10

Define motor protein

Answer 10

A protein that converts chemical energy into mechanical work. They contract causing muscles to contract. They also help with cilia and flagella movement, and the movement of internal cell contents around the cytoplasm

Question 11

Define storage protein

Answer 11

A protein that is a reserve of amino acids and metal ions

Question 12

Define Amino acid

Answer 12

Amino acids are molecules that combine to form proteins, they are joined together via a condensation reaction where water is a byproduct. A chain of amino acids ( A polypeptide) then folds to form a protein. They are composed of a hydrogen, a carboxyl group, an amino group and an R group. There are 20 different R groups, meaning that there are 20 different types of amino acid

Question 13

Define monomer

Answer 13

A molecule that forms that forms the basic unit of a polymer ( amino acid are the monomers of proteins)

Question 14

Define Polymer

Answer 14

A large molecule that is made up of small, repeated monomer subunits ( proteins are the polymer of amino acids)

Question 15

Define primary structure

Answer 15

The first level of protein structure, which is the order of amino acids in the chain

Question 16

Define secondary structure

Answer 16

The level of protein structure in which the protein folds and coils, depending on hydrogen bonds formed between different amino acids, into either alpha helixes, beta pleated sheets, or random coils

Question 17

Define Tertiary structure

Answer 17

The 3D shape of the protein- which builds on the secondary structure. The tertiary structure is primarily due to interactions between the R groups of the amino acids that make up the protein, and stronger disulphide bridges between cytseine amino acids. Generally in an aqueous environment, hydrophillic R groups are on the outside, and Hydrophoblic R groups are on the inside

Question 18

Define Quarternary structure

Answer 18

The level of protein structure where 2 or more polypeptide chains bond together, or prosthetic groups are attached to form a fully functional protein ( ie Haemoglobin is made of 4 polypeptide subunits, each containing an iron atom embedded in a haem prosthetic group

Question 19

Define prosthetic group

Answer 19

A non protein group bound to a protein. For example, a vitamin or ion

Question 20

Define DNA

Answer 20

Deoxyribonucleic acid is a molecule composed of two polynucleotide chains that coil around each other to form a double helix carrying genetic instructions for the development, functioning, growth and reproduction of all known organisms and many viruses.

Question 21

Define Chromosome

Answer 21

The structure made of protein and nucleic acid that carries genetic information. Humans have 46 chromosomes, 23 from each parent

Question 22

Define gene

Answer 22

A section of DNA that carries the code to make a protein

Question 23

Define genome

Answer 23

The complete set of DNA within an organism- it is heritable and passed on from parents to offspring

Question 24

Define Nucleic acid

Answer 24

The class of macromolecules that includes DNA and RNA. All nucleic acid are polymers made out of nucleotide monomers

Question 25

Define Nucleic monomers/ Nucleotides

Answer 25

the monomer unit of nucleic acid. Made up of a nitrogen containing base- Adenine, Thymine, Guanine or Cytosine , a 5 carbon deoxyribose sugar group and a phosphate group. With the 5 carbons in the sugar being labelled 1’, to 5’ , with the 1’ end being connected to the nitrogen base, and the 5’ end being attached to the phosphate group.

Question 26

Define Phosphodiester group

Answer 26

The strong convalent chemical bond linking a five- carbon sugar to a phosphate group

Question 27

Define Sugar- phosphate backbone

Answer 27

the strong covalently linked chain of 5 carbon sugar molecules and phosphate groups in a nucleic acid chain

Question 28

Define antiparallel

Answer 28

A characteristic of DNA strands, describing how each strands, describing how each strand runs in an opposite direction to the other. One strand runs in a 3’ to 5’ prime direction and the other runs in a 5’ to 3’ prime direction

Question 29

Define complementary base pairing

Answer 29

Describes which nucleotides can form hydrogen bonds with eachother- C & G, and A & T

Question 30

Define double helix

Answer 30

double stranded DNA in the nucleus of eukaryotic cells forms a double helix structure, where each DNA strand wraps around a central axis

Question 31

Define Nuclear DNA

Answer 31

DNA that is located in the nucleus of a cell

Question 32

What is RNA?

Answer 32

A single stranded nucleic acid chain made up of nucleotides. Includes mRNA, rRNA, and tRNA. It primarily assists with protein synthesis. It has a similar structure to DNA, except it has a ribose 5 carbon sugar, which has 1 more oxygen than deoxyribose molecule. It also has uracil instead of thymine.

Question 33

What is messenger RNA?

Answer 33

Produced during transcribed during transcription Carries genetic information from the DNA to the ribosomes for protein synthesis.

Question 34

What is transfer RNA?

Answer 34

RNA that recognises individual codons on the mRNA strandand adds the corresponding amino acid to the polypeptide chain during protein synthesis

Question 35

Define anticodon

Answer 35

The sequence of three nucleotides on a tRNA molecule that recognises a specific sequence of 3 nucleotides ( codon) on an mRNA strand

Question 36

What is Ribosomal RNA?

Answer 36

RNA that is a key structural component of ribosomes, which assemble proteins

Question 37

Define codon/ triplet

Answer 37

The sequence of 3 nucleotides in mRNA coding for one amino acid in the final polypeptide chain. There are also specific codons and triplets that instruct the cell to start and stop protein synthesis

Question 38

Define non- overlapping

Answer 38

The genetic code is nonoverlapping, i.e.,the adjacent codons do not overlap. A nonoverlapping code means that the same letter is not used for two different codons. In other words, no single base can take part in the formation of more than one codon.

Question 39

Define degenerate

Answer 39

A property of the genetic code which means that a single amino acid can be coded for by more than 1 codon

Question 40

What is transcription and how does it work?

Answer 40

Transcription is the first step in gene expression, in which information from a gene is used to construct a functional product such as a protein. The goal of transcription is to make a RNA copy of a gene’s DNA sequence.

1. Initiation- RNA polymerase binds to a sequence of DNA called the promoter, found near the beginning of a gene. Each gene has its own promoter. Once bound, RNA polymerase separates the DNA strands, providing the single-stranded template needed for transcription.
2. Elongation. One strand of DNA, the template strand, acts as a template for RNA polymerase. As it “reads” this template one base at a time, the polymerase builds an RNA molecule out of complementary nucleotides, making a chain that grows from 5’ to 3’. The RNA transcript carries the same information as the non-template (coding) strand of DNA, but it contains the base uracil (U) instead of thymine (T).
3. Termination. Transcription ends when the RNA polymerase reaches the termination sequence of a gene, signalling the end of transcription. The RNA polymerase then detaches, releasing the pre-mRNA molecule, and the DNA molecule winds up again into a double helix

Question 41

Define Termination sequence

Answer 41

a sequence of DNA that signals the end of transcription

Question 42

Define transcription factor

Answer 42

proteins that bind to the promoter region and control the function of RNA polymerase

Question 43

Define template strand

Question 44

Define template strand

Answer 44

the strand of DNA transcribed by RNA polymerase to produce a complementary mRNA strand

Question 45

Define coding strand

Answer 45

The strand of DNA not transcribed by RNA polymerase, contains an identical sequence to the mRNA strand produced ( except thymine is replaced by uracil in mRNA)

Question 46

Define pre-mRNA

Answer 46

The immediate product of transcription of a DNA sequence. Requires modification before it can undergo translation

Question 47

What is RNA processing?

Answer 47

When an RNA transcript is first made in a eukaryotic cell, it is considered a pre-mRNA and must be processed into a messenger RNA (mRNA).

A 5’ cap is added to the beginning of the RNA transcript, and a 3’ poly-A tail comprised of a chain of adenine molecules are added to the end. These stabilise the mRNA and prevent it from degrading and allowing it to bind it to the ribosome during translation.

In splicing, an enzyme called spliceosome removes introns and the remaining exons are stuck back together.

Sometimes exons are removed during the splicing process, meaning that a pre-mRNA strand could produce many different mRNA molecules, depending on which exons are spliced out.

Question 47

What is RNA processing?

Answer 47

When an RNA transcript is first made in a eukaryotic cell, it is considered a pre-mRNA and must be processed into a messenger RNA (mRNA).

A 5’ cap is added to the beginning of the RNA transcript, and a 3’ poly-A tail is added to the end.

In splicing, an enzyme called spliceosome removes introns and the remaining exons are stuck back together.

Some genes can be alternatively spliced, leading to the production of different mature mRNA molecules from the same initial transcript.

Question 48

Define introns

Answer 48

sequences of DNA that do not code for proteins. They are spliced out during RNA processing.

Question 49

Define exon

Answer 49

Sequences of DNA that code for proteins. They make up the mRNA molecule.

Question 50

What is translation and how does it work?

Answer 50

Translation is the process whereby an mRNA sequence is used to produce a corresponding amino acid sequence to build a polypeptide

1. Initiation. The small ribosomal subunit attaches to the 5’ end of the mRNA strand, and reads it until it reaches a a start codon (AUG). Then a tRNA molecule with the complemetary anticodon ( UAC) binds to the ribosome and delivers the amino acid ( UAC codes for methionine ( met)). The large ribosomal subunit then also binds to the mRNA and translation can begin
2. Elongation. After the first amino acid is attached, the mRNA is fed through the ribosome so the next codon can be matched to a new complementary tRNA. The new tRNA delivers the specific amino acid, which attaches to the met with a peptide bond via a condensation polymerase reaction. The first tRNA molecule then leaves and is free to pick up another amino acid, and the next mRNA codon is exposed for more tRNA delivered amino acids to add to the growing amino acid chain.
3. Termination- The reading of mRNA, delivery of amino acids by tRNA, and linking of amino acids in a polypeptide chain continues until the ribosome reaches a stop codon on the mRNA. The stop codon signals the end of translation as there are no corresponding tRNA molecules. The polypeptide chain is then released by the ribosome, into the cytosol or endoplasmic reticulum

Question 51

Define regulatory gene

Answer 51

A gene that is involved in the production of a substance that controls or regulates the expression of one or more genes, such as the gene that codes for a repressor protein that inhibits the activity of an operator gene.

Question 52

Define structural gene

Answer 52

Structural genes do not make proteins that are involved in the regulation of other genes, they encode for proteins that have a role in the structure or function of an organism

Question 53

What is the lac operon and how does it work ?

Answer 53

E. coli bacteria can break down lactose, but it’s not their favorite fuel. If glucose is around, they would much rather use that. Glucose requires fewer steps and less energy to break down than lactose. However, if lactose is the only sugar available, the E. coli will use it as an energy source.
To use lactose, the bacteria must express the lac operon genes, which encode key enzymes for lactose uptake and metabolism. To be as efficient as possible, E. coli should express the lac operon only when two conditions are met: Lactose is available, and Glucose is not available.

The lac operon contains a regulatory genes, promoter region, operator region, and the structural genes: lacZ, lacY, and lacA. Its expression is regulated by a repressor protein and environmental lactose levels.

When lactose levels are high, some of it is converted into allolactose ( which involves a slight change in chemical structure). Allolactase binds to and changes the shape of the repressor protein, causing the repressor protein to disconnect from the DNA strand.

This means the RNA polymerase can begin transcription of the lac operon, and the three structural proteins encoded by the structural genes lacZ, lacY, and lazA are produced.

The ultimate result is that these structural proteins break down lactose into glucose and galactose, and glucose can be used in cellular respiration. When the lactose is eventually used up the allolactose releases the repressor, which will once again inhibit transcription of the structural genes.

Question 54

Define repressor protein

Answer 54

a repressor is a DNA- or RNA-binding protein that inhibits the expression of one or more genes by binding to an operon

Question 55

Define operon

Answer 55

A cluster of linked genes that all share one promoter region and are transcribed at the same time

Question 56

Define promoter

Answer 56

The sequence of DNA to which RNA polymerase binds