1.3 - Gene Expression

Question 1

What 6 elements to Proteins contain?

Answer 1

Hydrogen, oxygen, nitrogen, carbon and often contain sulphur and phosphorus.

Question 2

What are proteins made up of?

Answer 2

sub-units called amino acids.

Question 3

How many essential amino acids are there?

Answer 3

There are 20 essential amino acids.

Question 4

How are proteins held in a 3-Dimensional shape?

Answer 4

Peptide bonds, hydrogen bonds and other interactions between individual amino acids.

Question 5

What are chains of amino acids called?

Answer 5

Polypeptide chains.

Question 6

What determines the proteins structure and function?

Answer 6

The sequence of amino acids.

Question 7

What two 3D shapes can proteins be?

Answer 7

Globular (round) or Fibrous (flattened)

Question 8

Give an example of a Globular protein.

Answer 8

Antibody

Question 9

Give an example of a Fibrous protein.

Answer 9

Keratin

Question 10

What is a gene?

Answer 10

A section of DNA which carries the code for the production of proteins.

Question 11

Define Genotype.

Answer 11

The types of gene an organism possesses - determined by the sequence of DNA bases.

Question 12

Define Phenotype.

Answer 12

Physical characteristics of an organism - determined by proteins synthesised as a result of gene expression.

Question 13

What is gene expression influenced by?

Answer 13

intra- and extra-cellular environmental factors.

Question 14

How many genes in a cell are expressed?

Answer 14

only a fraction.

Question 15

What is gene expression controlled by?

Answer 15

The regulation of transcription and translation.

Question 16

What is the second type of nucleic acid in the cell?

Answer 16

RNA. (ribose nucleic acid)

Question 17

What does RNA do?

Answer 17

plays a vital role in the production of protein from the code in DNA.

Question 18

What does an RNA nucleotide looklike?

Answer 18

A phosphate connects onto a ribose sugar and that connects onto a base.

Question 19

Give 3 comparisons between DNA and RNA.

Answer 19

DNA is double stranded, has a deoxyribose sugar and its complementary base pairs are (adenine + thymine, Guanine + Cytosine) Whereas RNA is single stranded, has a ribose sugar and its complementary base pairs are (Adenine + Uracil, Guanine and Cytosine.)

Question 20

What is mRNA?

Answer 20

Messenger RNA, formed in nucleus from free nucleotides, carries copy of DNA code from nucleus to ribosome. - where protein synthesis occurs.

Question 21

What is mRNA made up of?

Answer 21

Sequences of 3 nucleotides (triplet of bases) called codons.

Question 22

What is tRNA?

Answer 22

Transfer RNA, collects specific amino acids and brings them to ribosome to build proteins.

Question 23

What is the structure of tRNA?

Answer 23

Made of a single chain of nucleoides, folded into a 3D structure held by hydrogen bonds.

Question 24

What is rRNA?

Answer 24

Ribosomal RNA, combines with proteins to create the ribosome.

Question 25

What is transcription?

Answer 25

Transcription is the synthesis of mRNA from a section of DNA.

Question 26

Explain process of transcription

Answer 26

- transcription of a gene starts from a region of DNA known as the promoter - RNA polymerase is responsible for transcription, binds promoter, unwinds DNA, adds nucleotides onto end of growing molecule of mRNA - the mRNA will be complementary to the DNA - the molecule elongates until it reaches the terminator sequence - the molecule produced is called the primary transcript

Question 27

What is translation?

Answer 27

The synthesis of protein following the code within the mature mRNA transcript

Question 28

What is the process of translation

Answer 28

1. Ribosome binds to 5' end of the mRNA so that start codon is in site P 2. Next a tRNA carrying its amino acid becomes attached to site p as the mRNA start codon bonds with its complementary tRNA anti codon 3. Another tRNA becomes attached at site A, the mRNA codon bonds to its complementary tRNA anticodon carrying a specific amino acid 4. A peptide bond then forms between the two amino acids at site P and A 5. The tRNA from site p is moved to site E and released 6. The ribosome then moves along the codon 7. The translation process is repeated until it reaches a stop codon

Question 29

How can the same gene be used to make several different proteins?

Answer 29

Alternative RNA splicing | Post translational modification

Question 30

What is alternative RNA splicing

Answer 30

Under certain conditions alternative segments of RNA maybe treated as introns and exons, meaning one gene can produce several different mature mRNA transcripts, therefore several different proteins

Question 31

What is post translational modification

Answer 31

Once translation is completed proteins can be modified by Cleavage, a single polypeptide chain can be cleaved by enzymes to make it active Addition of other molecules, carbs and phosphate groups can be added to proteins

Question 32

Process of RNA splicing

Answer 32

After mRNA has been transcribed, introns are removed Remaining exons are spliced together to form a continuous sequence. This is the mature transcript, it leaves nucleus and goes to cytoplasm

Question 33

What does each codon code for?

Answer 33

Each codon codes for 1 amino acid