8: DNA, genes and protein synthesis

Question 1

What is a gene?

Answer 1

A sequence of DNA bases that codes for the amino acid sequence of a polypeptide OR a functional RNA

Question 2

What are the different RNA forms?

Answer 2

rRNA - Ribosomal
tRNA - Transfer
mRNA - Messenger

Question 3

How does DNA exist in eukaryotic cells?

Answer 3

Linear DNA molecules that exists as chromosomes
One long molecule of DNA
Found in the nucleus coiled very tightly

Question 4

How is a DNA wound in eukaryotic cells?

Answer 4

Really long so wound up around histone proteins to fit in nucleus

Question 5

What is a histone?

Answer 5

A protein that DNA is wound around in eukaryotic cells

Supports the DNA

Question 6

Other than the nucleus, where is DNA found in a eukaryotic cell?

Answer 6

Mitochondria and chloroplasts

Circular and shorter - no histones

Question 7

How does DNA exist in prokaryotic cells?

Answer 7

Shorter than chromosomes and circular
No histones
Super-coiling so it fits in the cell

Question 8

What is a cell’s genome?

Answer 8

Complete set of genes in the cell

Question 9

What is a cells’ proteome?

Answer 9

Full range of proteins that a cell is able to produce

Question 10

What does the order of bases determine?

Answer 10

The order of amino acids to form a particular polypeptide

Question 11

What is an amino acid coded by ?

Answer 11

DNA Triplet

Three bases from a gene

Question 12

What is the use of genes that don’t code for polypeptides?

Answer 12

Codes for functional RNA

Question 13

What is functional RNA?

Answer 13

RNA other than mRNA

Performs special tasks (tRNA & rRNA)

Question 14

What is a chromosome?

Answer 14

A thread-like structure made of protein and DNA

Question 15

What is an allele?

Answer 15

One of a number of alternative forms of a gene

Question 16

What is the locus?

Answer 16

Position of a gene on a chromosome/DNA molecule

Question 17

What is a gene?

Answer 17

A section of DNA on a chromosome coding for the amino acid sequence for one or many polypeptides

Question 18

What does homologous mean?

Answer 18

A pair of chromosomes, one maternal and one paternal

Same gene loci therefore determines same features

Question 19

What is degenerate code?

Answer 19

This is when amino acids are coded for by more than one triplet of bases

Question 20

What is an intron?

Answer 20

Non-coding sequences of DNA in a gene

Question 21

What is an exon?

Answer 21

Sequences of bases that code for amino acids in a gene

Question 22

Do prokaryotic cells contain introns?

Answer 22

No

Question 23

Why is the rate of replication faster in prokaryotic cells?

Answer 23

No membrane has to be synthesised

Question 24

How many different bases are there in DNA?

Answer 24

4 different bases

Question 25

How many different triplets are there and how is this number found?

Answer 25

64 | 4 bases ^3 = 64

Question 26

How is genetic code universal?

Answer 26

Same specific base triplets code for same amino acids in all living things

Question 27

What are triplets than do not code for an amino acid?

Answer 27

Nonsense triplets

Question 28

What are stop triplets?

Answer 28

Stop signals to terminate a protein chain

Question 29

Why does DNA need to be transcribed to RNA?

Answer 29

DNA confined to nucleus as too large to move through nuclear pores Protein synthesis occurs in cytoplasm

Question 30

What is a codon?

Answer 30

Sequence of three bases of mRNA that codes for an amino acid

Question 31

Why are introns removed for protein synthesis?

Answer 31

To prevent gaps in the amino acid sequence which would cause gaps in the protein

Question 32

What is the difference between DNA & RNA?

Answer 32

``` RNA is a single strand Contains uracil (U) instead of thymine (T) ```

Question 33

What are the characteristics of messenger RNA (mRNA)?

Answer 33

``` Single strand & single helix Located in nucleus & cytoplasm Bases: AUGC Ribose sugar Function: Transcription ```

Question 34

What are the characteristics of DNA?

Answer 34

``` Double strand & double helix Located in nucleus Bases: ATGC Deoxyribose sugar Function: Hereditary material ```

Question 35

What are the characteristics of transfer RNA (tRNA)?

Answer 35

``` Single strand & clover-leaf Located in cytoplasm Bases: AUGC Ribose sugar Function: Translation ```

Question 36

What is the function of transfer RNA?

Answer 36

Carries amino acids for proteins to ribosomes Each tRNA has a specific sequence of three bases at one end, called an anticodon They have an amino acid binding site

Question 37

What are the two main stages of protein synthesis?

Answer 37

Transcription | Translation

Question 38

What occurs in transcription?

Answer 38

DNA is used to synthesise a molecule of mRNA that will carry the code to the ribosomes

Question 39

Describe the transcription process

Answer 39

DNA helicase breaks hydrogen bonds and exposes nucleotides RNA polymerase binds to promoter region and adds free nucleotides to form pre-mRNA Stops once it reaches a stop region pre-mRNA leaves the nucleus by the nuclear pores

Question 40

What is pre-mRNA?

Answer 40

Newly formed mRNA which contains exons and introns | Also contains promoter regions

Question 41

What is a promoter region?

Answer 41

Recognition sites for the RNA polymerase that indicate where to start copying the DNA

Question 42

What is splicing of pre-mRNA?

Answer 42

The removal of the introns and remaining exons are joined together Ends of mRNA is "capped" which allows recognition which is required for translation

Question 43

How are amino acids joined to tRNA?

Answer 43

Using energy from ATP and a specific enzyme

Question 44

What organelle is required for translation?

Answer 44

Ribosomes

Question 45

What base sequence is always found on tRNA and why?

Answer 45

ACC | This is where amino acids bind

Question 46

Where does translation occur?

Answer 46

In the cytoplasm at the ribosomes

Question 47

What occurs in translation?

Answer 47

Amino acids are joined to create a polypeptide chain | This is done using the codons from mRNA to determine specific amino acids

Question 48

Describe the translation process

Answer 48

mRNA attaches to ribosome and tRNA carries amino acids to it tRNA molecule with anticodon attaches to complementary bases on codon on the mRNA This occurs with another tRNA and the amino acid from each are joined by a peptide bond This continues until it reaches a stop codon

Question 49

What happens to the tRNA after the amino acid has formed a peptide bond with another in the ribosome?

Answer 49

It moves away from the ribosome | Leaves the amino acids behind

Question 50

How can the genetic code be described?

Answer 50

Non-overlapping Degenerate Universal

Question 51

Why is the genetic code described as non-overlapping?

Answer 51

As the base triplets don't share their bases

Question 52

What is the role of RNA polymerase in transcription?

Answer 52

Join and attach nucleotides to form an RNA molecule

Question 53

Why can splicing cause a gene to code for different proteins?

Answer 53

The exons can be joined in different orders to produce different proteins

Question 54

Mutation of protein question answer

Answer 54

Change in DNA, base sequence, triplet Different amino acids used to make a protein Different sequence and primary to tertiary structure Different tertiary means different bonds form Protein has different shape (enzymes active site changes so no enzyme-substrate complex can form)