Mod 5 HEREDITY: DNA and Polypeptide synthesis

Question 1

Outline the differences between prokaryotic and eukaryotic DNA

Answer 1

Prokaryotic DNA is:
- Not bound to any proteins, hence does not form chromatin

• No introns present, hence genomes are compacts
• Contains plasmids
• Instead of a nucleus, there is a nucleoid where DNA is able to freely float

Eukaryotic DNA:
- Is held within the nucleus

• Bound to histone proteins
• Contains large amount of introns
• Does not contain plasmids except some organelles (i.e., mitochondria and chloroplast)
• Linear structure

Question 2

How is prokaryotic DNA packaged?

Answer 2

Packaged via nucleoid-associated proteins that are responsible for making the DNA in a loop-form structure

Question 3

How is eukaryotic DNA packaged?

Answer 3

Packaged via histone proteins, giving them their linear structure

Question 4

Identify the quantity of prokaryotic DNA

Answer 4

Typically, contains one chromosome that have few copies of it, having plasmids and base pair ranges of 100k - 20 million

Question 5

Identify the quantity of eukaryotic DNA

Answer 5

Contains multiple chromosomes with no plasmids, and base pair range could reach billions.

Question 6

Identify the replication of prokaryotic DNA

Answer 6

Prokaryotes can replicate their DNA fast, of 2000 base pairs per second, 1 replication fork

Question 7

Identify the replication of eukaryotic DNA

Answer 7

Eukaryotic cells replicate their DNA slow, of about 100 base pairs per second, with multiple replication forks

Question 8

Identify the information content of prokaryotic DNA

Answer 8

Prokaryotic cells are organised in operons; they code for a variety of proteins. One version of each gene is present.

Question 9

Identify the information content of eukaryotic DNA

Answer 9

Eukaryotic cells are organised in genes that encode for a specific protein. Consist of two versions of each gene, one from each parent.

Question 10

Define polypeptide

Answer 10

Many peptide bonds connecting to the many amino acid chains

Question 11

Define protein

Answer 11

A functioning complex composed of one or more polypeptides

Question 12

Define amino acids

Answer 12

Building blocks of proteins, determined by a nucleotide sequence

Question 13

Outline the two stages of polypeptide synthesis

Answer 13

Transcription and translation

Question 14

Describe the process of transcription

Answer 14

Transcription is the first step of polypeptide (protein) synthesis, in which a messenger RNA (mRNA) is created via a stand of DNA as a template. DNA unwinds and unzips, with one strand being copied to create a complementary mRNA molecule. This is catalysed with the help of RNA polymerase, an enzyme responsible for the adding of complementary base pairs. All of this occurring in the cell nucleus of the cell, readying to be sent out of the nucleus into the cytoplasm for the next stage.

Question 15

Describe the process of translation

Answer 15

Translation follows transcription, in which it is responsible for translating the mRNA into an amino acid sequence. This is done with the help of tRNA (transfer). tRNA is responsible for matching the amino acid of the mRNA codon via complementary anticodon. All of this occurs in the cytoplasm of the cell.

Question 16

True or False: In the synthesis of polypeptides, adenine pairs with uracil in the DNA strand being transcribed.

Answer 16

False. In polypeptide synthesis, adenine pairs with uracil in the mRNA strand being transcribed from the DNA, not within the DNA strand itself.

Question 17

Outline the differences between mRNA and tRNA

Answer 17

mRNA provides the sequence of codons that determine the order of amino acids in the protein, where tRNA matches its anticodon with the codon on the mRNA to add the correct amino acid to the growing polypeptide chain

mRNA generally has a short lifespan, quickly degraded after translation to prevent unnecessary protein production. tRNA is more stable, and can be reused multiple times during translation.

Question 18

Assess the importance of mRNA and tRNA in transcription and translation

Answer 18

In the transcription and translation process, tRNA and mRNA are incredibly important in the formation of proteins. In transcription, the mRNA strand forms from the template strand DNA, read by RNA polymerase enzyme. Here is then sent from the nucleus to the ribosomes in the cytoplasm. In the absence of mRNA, the sequence of amino acids in DNA codd would not form, meaning that proteins cannot be produced and the organism ceases to exist. In the absence of tRNA, the mRNA sequence will have no way to be converted into amino acids. Consequently, the polypeptide chains would not be formed, leading to no synthesis of proteins that play a vital role in our body.

Question 19

Analyse the function and importance of polypeptide synthesis

Answer 19

Polypeptide synthesis is the process of assembling amino acids into functioning proteins, comprising of transcription where DNA is converted into mRNA, carrying genetic information from nucleus to cytoplasm, and translation where ribosomes with the help of tRNA, decodes mRNA into polypeptide chains that form the bases of proteins. To code for a functional protein, it requires accurate translation to code for a protein that carries a specific function in the body. For this reason, organisms are able to produce necessary functional proteins to sustain life.

Question 20

Define gene expression

Answer 20

Genes are used in protein synthesis to influence physical characteristics of species.

Question 21

Define and provide examples of a phenotype

Answer 21

Physical expression of the genotype (I.e., eye and hair colour)

Question 22

Identify traits that are not influenced by the environment

Answer 22

Blood type
Eye colour
Genetic disorders such as cystic fibrosis

Question 23

Identify traits that are influenced by the environment

Answer 23

Breast cancer
Schizophrenia
Hypertension

Question 24

How are constitutive genes and regulated genes expressed?

Answer 24

Constitutive genes are always expressed and not as likely to be influenced by the environment, whereas regulated genes are expressed/silenced depending on environment through epigenetic marks

Question 25

Recall TWO relevant case studies for environmental influence

Answer 25

Temperature has an effect on reptile gender, affected in the reptile egg incubation temperature during the thermosensitive period. This determines the sex of an offspring, as their gonadal tissue is responsive to the temperature. For instance. European pond turtle have an incubation period of 75–80 days. 25°C = offspring born as males. 28.5°C = eggs will carry as male and female.
30°C = offspring are females

Hydrangea flower colour is determined by the pH of soil. Acidic soils produce blue blooms and alkaline soils produce pink, despite being genetically identical hydrangea. Here highlights the influence of the environment on the phenotypic expression.

Question 26

Proteins have four types of structure. Identify them.

Answer 26

Primary
Secondary
Tertiary
Quaternary

Question 27

Describe primary structure

Answer 27

Amino acid sequence that is linear, held by covalent peptide bonds. This forms a peptide chain.

Question 28

Describe secondary structure

Answer 28

The protein coils and folds due to hydrogen bonds between peptides.

Question 29

Recall alpha-helix and beta-sheet

Answer 29

They are ways in which proteins are structured under secondary forms. Alpha-helix is when the backbone of the protein coils around a helix axis in clockwise direction.

Beta sheets are when the protein’s backbone is nearly fully extended.

Question 30

Describe tertiary structure

Answer 30

A three-dimensional folding of the protein, determined by bonds between side chains

Question 31

Describe quaternary structure

Answer 31

The arrangement of multiple polypeptide subunits, forming a functional protein. Weakened hydrogen bonds that are easily broken by changes in the environment, therefore the protein can lose its structure and becomes denatured.

Question 32

Identify what fibrous proteins are, providing an example

Answer 32

Molecules made from repetitive amino acid sequences, maintaining the structural integrity and function of various tissues and organs in the body, such as actin, providing assistance in muscle contraction.

Question 33

Identify what globular proteins are, providing an example

Answer 33

Complex proteins that consist of tertiary/quaternary structure, playing various roles in cellular functions, such as catalysis, transport, regulation, and immune response. For instance, enzymes.

Question 34

List the type of fibrous protein

Answer 34

Contractile proteins

Question 35

Define contractile proteins and provide an example

Answer 35

Cell movement and muscle contraction For instance, actin is involved in muscle contraction

Question 36

List and define the types of globular proteins (THESIS), providing an example of each.

Answer 36

Transport proteins - Transports molecules within the body, such as haemoglobin, assisting in carrying oxygen throughout the body.

Hormonal proteins - Messenger proteins coordinating cellular functions, such as insulin.

Enzymes - Speed up the rate of chemical reactions. For instance, lactase breaks down lactose found in milk.

Structural proteins - Provide support and strength, such as keratin

Immunoglobulins - Defends against pathogens, such as antibodies.

Storage proteins - Store amino acids that are used for growth, such as ferritin, storing iron in the body.