Gene Expression & Cellular Differentiation

Question 1

Allele

Answer 1

The different forms of a gene

Question 2

Genotype

Answer 2

The alleles present in an organism

Question 3

Phenotype

Answer 3

The appearance of an organism

Question 4

Gene expression

Answer 4

When a particular gene is producing the protein that it codes for by protein synthesis

Question 5

RNA

Answer 5

RNA is a single stranded and composed of nucleotides containing ribose sugar, phosphate and 4 bases Cytosine, Guanine, Adenine and Uracil (instead of Thymine)

Question 6

Differences between DNA and RNA

Answer 6

DNA found in nucleus, RNA found in nucleus/cytoplasm
DNA has 2 strands, RNA has 1 strand
DNA sugar is deoxyribose, RNA sugar is ribose
DNA A is paired to Thymine, RNA A is paired to Uracil

Question 7

mRNA (messenger RNA)

Answer 7

Found in nucleus/cytoplasm/rough ER
it carries a copy of DNA code from the nucleus to ribosome
each triplet of babes on the mRNA molecule is called a CODON and codes for a SPECIFIC AMINO ACID

Question 8

tRNA (transfer RNA)

Answer 8

Found in cytoplasm/ribosome
carries specific amino acid from cytoplasm to ribosome
tRNA molecules have an ANTICODON at one end and an attachment site for a SPECIFIC AMINO ACID at other end

Question 9

rRNA (ribosomal RNA)

Answer 9

Found in ribosome

take part in translation of mRNA to amino acid code

Question 10

Codon and anticodon

Answer 10

codon- sequence of 3 nucleotides (bases) found on mRNA
anti-codon- sequence of three nucleotides at the bottom of the tRNA molecule, which is complementary to the CODON on mRNA

Question 11

Start codon and Stop

Answer 11

start codon is the first codon on a mature mRNA transcript

stop codon are codons found within mRNA that signal a termination of the process of protein translation

Question 12

Protein Synthesis

Answer 12

Cells express their genes by converting the genetic message into protein.
two stages called transcription and translation

Question 13

Transcription (mRNA production)

Answer 13

1. RNA POLYMERASE enzyme moves along the section of DNA unwinding the double helix
2. HYDROGEN BONDS between base pairs break which allow the unwinding of the double helix
3. As RNA polymerase breaks the bonds, it synthesises a PRIMARY TRANSCRIPT of mRNA using RNA nucleotides which form hydrogen bonds with the exposed DNA strand by complementary base pairing to the DNA nucleotides
4. primary transcript of mRNA is SPLICED to produce mature mRNA transcript
5. mature mRNA transcript is ready to leave nucleus and travel to ribosome

Question 14

RNA splicing

Answer 14

This removes sections NON-PROTEIN CODING sections of mRNA called INTRONS and joins together the PROTEIN CODING SECTIONS of mRNA called EXONS to form a mature transcript

Question 15

mRNA Translation

Answer 15

1. translation of mRNA begins at a START codon and ends at a STOP codon
2. anti-codon on tRNA join to mRNA codons by COMPLEMENTARY BASE PAIRINGS
3. as more tRNA molecules arrive at mRNA carrying SPECIFIC amino acids, this translates the genetic code into a SEQUENCE OF AMINO ACIDS
4. PEPTIDE BONDS form between amino acids on the sequence
5. each tRNA molecule then leaves the ribosome and a POLYPEPTIDE (chain of many amino acids) is formed after the translation of mRNA

Question 16

Alternative RNA splicing

Answer 16

one gene - many proteins
different mature transcripts are made from the primary transcript, This depends on which exons are spliced together on mature mRNA transcript

Question 17

Shapes of proteins

Answer 17

• polypeptide chains (of amino acids) which are folded to give their 3-D shape are held together by HYDROGEN BONDS and other interactions between individual amino acids.
• proteins have a large variety of shapes which determines their functions.

Question 18

Cellular Differentiation

Answer 18

process by which a cell expresses certain genes to produce protein characteristics for that type of cell.
this allows cells to carry out specialised functions
MERISTEMS are regions of unspecialised cells in plants that can divide (self-renew) and/or differentiate
STEM CELLS are unspecialised cells in animals that can divide (self-renew) and/or differentiate

Question 19

Differentiation in animal cells

Answer 19

EMBRYONIC STEM CELLS are found in VERY EARLY EMBRYONIC TISSUE which, as all the genes can be switched on, are able to DIFFERENTIATE INTO ALL CELL TYPES that make up an organism and are said to be PLURIPOENT

TISSUE (adult) stem cells are involved in the growth, repair and renewal of cells in a specific tissue. they can DEVELOP INTO ALLL CELLS OF A SPECIFIC TYPE OF TISSUE and are said to be MULTI-POTENT.

Question 20

Therapeutic and research use of stem cells

Answer 20

• therapeutic use of stem cells involve THE REPAIR OF DAMAGED OR DISEASED ORGANS OR TISSUE
• research with stem cells being used as MODEL CELLS to study how diseases develop or for drug testing
• stem cell research gives info on how cell processes such as CELL. GROWTH, DIFFERENTIATION, GENE REGULATION work
• ethical issue of embryonic stem cells is that they involve DESTRUCTION OF EMBRYOS