Topic 4 - DNA, Genes, Chromosomes, And Protien Synthesis

Question 1

What are the features of prokaryotic DNA?

Answer 1

• It is short and arranged in a circular structure.
• No association with histone proteins, meaning it is not organised into chromosomes.
• The DNA is naked, existing freely in the cytoplasm within a region called the nucleoid.
• Often contains additional small, circular DNA molecules known as plasmids, which carry non-essential genes like those for antibiotic resistance.

Question 2

What is a plasmid?

Answer 2

A small, extra-chromosomal DNA molecule in prokaryotes, often carrying beneficial genes.

Question 3

What is nuclear DNA?

Answer 3

• found in the nucleus, organised into linear chromosomes
• associated with histone proteins, forming a complex called chromatin
• chromosomes are condensed forms of DNA, visible during cell division

Question 4

What is organellar DNA?

Answer 4

Mitochondria and chloroplasts contain their own DNA, which is:
- Short, circular, and similar to prokaryotic DNA.
- Not associated with histones.
- This DNA codes for proteins specific to the organelle’s function.

Question 5

What is the structure of mitochondrial and chloroplast DNA?

Answer 5

DNA in mitochondria and chloroplasts is short, circular, and not associated with histone proteins, similar to prokaryotic DNA.

Question 6

What is the location of mitochondrial DNA?

Answer 6

Mitochondrial DNA is found in the mitochondria and encodes proteins essential for aerobic respiration, such as enzymes in the electron transport chain.

Question 7

What is the location of chloroplast DNA?

Answer 7

Chloroplast DNA is found in the chloroplasts and encodes proteins and enzymes required for photosynthesis, such as those in the light-dependent and light-independent reactions.

Question 8

How is mitochondrial DNA inherited?

Answer 8

Maternally inherited, this makes it useful for tracing maternal ancestry.

Question 9

What is a gene?

Answer 9

A specific sequence of DNA located on a chromosome which codes for the production of one or more polypeptide chains.

Question 10

What is the structure of a gene?

Answer 10

A gene consist of coding regions called exons and non-coding regions called introns in eukaryotes.
The sequence of bases in a gene determines the amino acid sequence in a polypeptide.

Question 11

What is the location of the gene?

Answer 11

Found on a chromosome with each gene occupying a specific locus.

Question 12

What is the three features of the genetic code?

Answer 12

Universal: the same code is used in almost all living organisms.
Degenerate: multiple codons can code for the same amino acid.
Non-overlapping: each codon is red separately.

Question 13

What is a genes role in protein synthesis?

Answer 13

Genes are transcribed into messenger RNA during transcription mRNA is then translated into polypeptides during translation.

Question 14

What is the locus of a gene?

Answer 14

The precise position of a gene on a chromosome each gene has a unique locus on a specific chromosome.

Question 15

What are alleles?

Answer 15

Different forms of a gene that occupy the same locus and homologous chromosomes.

Question 16

What are homologous chromosomes?

Answer 16

In diploid organisms chromosomes come in homologous pairs so there are two loci for each gene one on each chromosome in the pair.

Question 17

What is a mutation?

Answer 17

Mutations can change the sequence of DNA at a locus potentially leading to genetic disorders or variations.

Question 18

What is the genetic code?

Answer 18

The sequence of bases on DNA that determines the sequence of amino acids in a poly peptide chain. The code is written in triplets where each group of three bases forms a codon that specifies a particular acid.

Question 19

What are the functions of non-coding DNA?

Answer 19

Control gene expression and are involved in the production of tRNA and rRNA, telomeres protect the ends of chromosomes from damage.

Question 20

What are promoter regions?

Answer 20

Non-coding regions where RNA polymer raised binds to initiate transcription.

Question 21

What are enhancer/silencers?

Answer 21

Non-coding regions that increase or decrease the rate of transcription.

Question 22

What is the genome?

Answer 22

It refers to the complete set of genetic material in an organism. This includes all the DNA present in the nucleus, mitochondria and chloroplast.

Question 23

What is the human genome project?

Answer 23

A major scientific initiative that mapped the entire human genome identify all the genes and their locations. This has improved our understanding of genetic diseases and paved the way for personalised medicine.

Question 24

What is RNA?

Answer 24

A single stranded nucleic acid involved in protein synthesis playing crucial roles as mRNA and tRNA. Unlike DNA, it contains the sugar rib and the base uracil instead of thymine.

Question 25

What is the general structure of RNA?

Answer 25

- Single stranded polynucleotide chain. - Contains the sugar ribose - Contains a phosphate molecule - Contains the nitrogenous base

Question 26

What is the structure of messenger RNA?

Answer 26

- Long single stranded molecule produced during transcription - Base sequence is complementary to the DNA template strand - divided into sequences of three bases called codons coding for a specific amino acid.

Question 27

What is the function of mRNA?

Answer 27

Carries the genetic code from DNA in the nucleus to the ribosomes in the cytoplasm where proteins are synthesised.

Question 28

What is the function of tRNA?

Answer 28

- transfers, the appropriate amino acid to the ribosome during translation - Matches its anticodon with the corresponding mRNA codon ensuring that the correct sequence of amino acids in the protein.

Question 29

What is the structure of tRNA?

Answer 29

- tRNA is a small clover shaped molecule made by folding into loop due to hydrogen bonding between complementary base pairs - At one end it has an anticodon a set of three bases complementary to an mRNA codon. - The other end has a binding site for a specific amino acid.

Question 30

What are the key differences between DNA and RNA?

Answer 30

RNA is a single-stranded DNA is double stranded. RNA contains uracil instead of thymine. RNA uses the sugar ribose while DNA uses deoxyribose.

Question 31

What is transcription?

Answer 31

The first age of protein synthesis during which a molecule of mRNA is produced from a DNA template. This process occurs in the nucleus of a eukaryotic cell.

Question 32

What is the first step of transcription?

Answer 32

1. The enzyme DNA helicase the hydrogen bonds between complementary base pairs causing the DNA to uncoil and expose the template strand.

Question 33

What is the second stage of transcription?

Answer 33

2. Free nucleotides align with the exposed bases on the template strand by complementary base pairing. The enzyme RNA polymerase catalyses the formation of phosphodiester bonds between adjacent RNA nucleotides creating a strand of mRNA.

Question 34

What is the third stage of transcription?

Answer 34

3. Transcription stops when RNA polymerase reaches a stop codon on the DNA template. The newly formed pre-mRNA strand detaches from the DNA.

Question 35

What is the fourth stage of transcription?

Answer 35

4. As RNA polymerase moves along the DNA the hydrogen bonds between the DNA strand reform behind it the DNA recoils into a double helix.

Question 36

What is the fifth stage of transcription?

Answer 36

5. Splicing - The pre-mRNA contains both introns and exons. Enzymes to remove the introns leaving a strand of mature mRNA that contains only exons. The mRNA then exit the nucleus through a nuclear attaches to a ribosome ready for translation.

Question 37

What is splicing?

Answer 37

The removal of introns from pre-mRNA in the nucleus.

Question 38

What is translation?

Answer 38

The process in which the genetic code carried by mRNA is decoded to synthesise a polypeptide chain.

Question 39

What is the first stage of translation?

Answer 39

1. The mRNA molecule binds to a ribosome in the cytoplasm, the ribosome reads the codons on the mRNA starting at the start codon.

Question 40

What is the second step of translation?

Answer 40

2. Transfer RNA collects specific amino acids from cytoplasm and carries them to the ribosome. It has a binding site for one specific amino acid and an anticodon which is complementary to the mRNA codon.

Question 41

What is the third stage of translation?

Answer 41

3. The amino acids attached to the tRNA molecules are joined together by peptide bonds catalysed by peptidyl transferase. After the bond formed the tRNA molecule detaches leaving amino acids behind.

Question 42

What is the fourth and final stage of translation?

Answer 42

4. The divide zone moves along the mRNA allowing for more tRNA molecules to attach add amino acids to the growing chain. This will continue and tell us stop codon is reached. Then the rivers releases the poly.