dna genes and protein synthesis

Question 1

what is a gene

Answer 1

a gene is a base sequence of DNA that codes for the amino acid sequence of a protein(polypeptide) or a functional RNA

Question 2

whats the definition for genome

Answer 2

all of the genes that code for a particular species

Question 3

what is genetic loci

Answer 3

the position of a gene on a chromosome is its locus

Question 4

what is an allele

Answer 4

each gene can exist in two or more different forms

Question 5

what is the difference between alleles

Answer 5

different alleles of a gene have slightly different nucleotide sequences but they still occupy the same position (locus) on the chromosome

Question 6

what is genetic code

Answer 6

the base sequence in a DNA molecule represented by the letters ATCG make up the genetic code. the genetic code is read in triplets of bases or codons

Question 7

how many bases codes for 1 amino acid

Answer 7

3 bases ( a triplet )

Question 8

what can some of the triplets code for

Answer 8

start and stop signals, these signals tell us where the individual genes start and stop . this ensures the cell reads the DNA correctly and can produce the correct sequences of amino acids .

Question 9

whats another feature of start and stop signals

Answer 9

they are complementary to eachother

Question 10

why is our genetic code read in triplets

Answer 10

there are four bases . if each base coded for an amino acid there would only be 4 amino acids that could be used
however there are 20 different amino acids
if every 2 bases coded for an amino acid then we would have 16 possibilities therefore we have triplet code as we have 64 combinations (4^3) and this results in triplets coding for the same amino acid ( as theres only 20 combinations and we have 64)

Question 11

what are the 3 main features of genetic code

Answer 11

• degenerate
  -non - overlapping
  -universal

Question 12

what is the definition for degenerate

Answer 12

More than one codon codes for each amino acid

Question 13

whats the definition for non-overlapping

Answer 13

the genetic code is read sequentially. each base is part of only one triplet

Question 14

whats the definition for universal

Answer 14

in all organisms the same triplet/ codon codes for the same amino acid

• the same triplet always codes for the same amino acid in all organisms

Question 15

whats non coding DNA

Answer 15

the genome within eukaryotic cells contains many non - coding sections of DNA which does not code for any amino acids

Question 16

what are the non coding sections called

Answer 16

introns

Question 17

what are the coding sections called

Answer 17

extons - the parts of a gene that do code for an amino acid

Question 18

explain how the change in one base along the DNA molecule may result in an enzyme becoming non functional

Answer 18

a different base might code for a different amino acid. the sequence of amino acids in the polypeptide produced would be different .this change to the primary structure may result in a different shaped tertiary structure and therefore the enzyme shape will be different and may not fit the substrate . the enzyme - substrate complex cannot form and so the enzyme is non functional

Question 19

What are the differences between DNA and RNA

Answer 19

-DNA is Double stranded whereas RNA is single stranded
-DNA contains thymine whereas RNA contains uracil
-DNA contains a deoxyribose sugar whereas RNA contains a ribose sugar
-DNA contains genetic information whereas RNA is used in protein synthesis
-DNA is found in the nucleus , chloroplasts and mitocondria whereas RNA is in the cytoplasm, ribosomes and nucleus

Question 20

What are the types of RNA

Answer 20

Transfer RNA , ribosomal RNA, messenger RNA

Question 21

What is protein synthesis

Answer 21

Where a sequence of bases in DNA determines and produces the sequence of amino acids in the proteins of an organism

Question 22

What’s messenger RNA

Answer 22

mRNA is a single stranded molecule . It is made up of a sugar phosphate backbone and exposed unpaired bases . Uracil bases are present instead of thymine

Question 23

What is tRNA , transfer RNA

Answer 23

It’s a single stranded RNA molecule . It has a distinctive folded structure with three hairpin loops that form the shape of a cloverleaf . Hydrogen bonds form between some of the bases if complementary
Amino acids bind to a specific region of the molecule
They have an anticodon found on the end and is complementary to a specific codon on the mRNA molecule

Question 24

What is ribosomal rRNA

Answer 24

A ribosome is made out of rRNA and proteins
Each ribosome consists of two separate RNA-protein complexes
RNA can be of varying sizes , commonly distinguished with small and large ribosome subunits . These rRNAs are vital in recognising mRNA and tRNA thus facilitating their binding and carrying out protein synthesis

Question 25

what is protein synthesis

Answer 25

the process of making proteins from DNA

Question 26

what are the two stages

Answer 26

transcription and translation

Question 27

what happens during transcription

Answer 27

makes a copy of the DNA called mRNA

Question 28

what happens during translation

Answer 28

where mRNA is read by ribosomes to produce a protein

Question 29

what are the steps for transcription

Answer 29

1) the DNA in the nucleus is first unwound from the double helix
2) the weak hydrogen bonds between the bases by the enzyme DNA helicase are broken
3) causes two strands to seperate
4) free RNA nucleotides in the nucleoplasm find their complementary base pair on the DNA template strand
5) a hydrogen bond forms between the RNA nucleotide base and the complementary base on the DNA
6) the enzyme RNA polymerase then catalyses the formation of the strong chemical bonds ( phosphodiester bond ) between the ribose sugar and phosphate groups of adjoining RNA nucleotides
7) the messenger pre - mRNA molecule is
formed
8) hydrogen bonds between the bases mRNA and the bases on the DNA break
9) the hydrogen bonds between the complementary bases on DNA reform and the DNA is wound back into a helix
10) after transcription the mRNA strand can be spliced and this means the introns are cut out and the extrons are joined back together

Question 30

6 marker describe transcription

Answer 30

1) DNA in the nucleus is unwound and DNA helicase breaks the hydrogen bonds
2) the two strands seperate and free RNA nucleotides in the nucleoplasm find their complementary base pair on the DNA template strand exposed bases
3)a hydrogen bond forms between the RNA nucleotide base and the complementary base on the DNA
4) RNA polymerase catalyses the formation of phosphodiester bonds between the ribose sugar and phosphate groups on adjoining RNA nucleotides
5) the pre mRNA molecule is formed
6)hydrogen bonds between the mRNA and DNA strand break
7) hydrogen bonds between the complementary bases on DNA reform and wind back into a helix
8) the pre mRNA strand is spliced and introns are cut out and exons are joined back together to form mRNA

Question 31

where does transcription occur

Answer 31

in the nucleus

Question 32

where does translation occur

Answer 32

in the cytoplasm

Question 33

what is translation

Answer 33

translation is the process where mRNA is read and translated into a protein . it occurs in the cytoplasm / on the ribosomes
and involves tRNA

Question 34

what are the steps for translation

Answer 34

1) the mRNA leaves the nucleus through a nuclear pore and enters the cytoplasm
2)a ribosome becomes attached to the mRNA
3) the genetic code is read in groups of 3 letters called codons
4)tRNA molecules have specific anticodons for each of the 20 amino acids
5) the complementary anticodon is attracted to the first codon , called an initiation codon on the mRNA and forms a weak hydrogen bond
6) this then repeats with every codon until the mRNA is all read
7)a peptide bond is formed between the adjacent amino acids
8) the first tRNA molecule becomes detached from its amino acid
9) the ribosome moves along the mRNA molecule
10) a stop codon is reached
11) a polypeptide chain has been formed and it can be released into the cytoplasm or other organelles
12) the tRNA molecules are activated after use by recombining with their specific amino acid (requires ATP)

Question 35

what happens with the polypeptide after protein synthesis

Answer 35

the amino acid chain is then sent to the rough endoplasmic reticulum and is folded through its secondary and tertiary structures to form a protein. then the folded proteins is sent to the golgi apparatus which modifies and packages the protein into a vesicle , this protein is then sent within the cell or outside of the cell where it is needed

Question 36

what is a proteome or complete proteome

Answer 36

the full range of different proteins the genome can code for or
the number of different proteins that a cell is able to produce at a given time

Question 37

what 6 points must you include in your translation 6 marker

Answer 37

• mRNA leaves the nucleus through the nuclear pore to ribosome
• tRNA molecules bring amino acids to ribosome
  -specific tRNA molecule for specific amino acid
  -aniticodon of tRNA is complementary to codon on mRNA
  -peptide bonds form between amino acids
  -tRNA detaches and collects another amino acid
  -ribosome moves along mRNA

Question 38

Give two structural differences between a molecule of messenger, RNA and a molecule of transfer RNA

Answer 38

MRNA does not have an amino acid binding site whereas tRNA does
MRNA is a straight chain, whereas tRNA is a cloverleaf

Question 39

Starting with mRNA in the cytoplasm, describe how translation leads to the production of a polypeptide

Answer 39

A ribosome attaches to the mRNA and the genetic code is red in codons. The ribosome moves to find the start codon tRNA molecules have specific anticodons for each of the 20 amino acids. The complimentary anti codon is carried and attracted to each codon on the mRNA and forms hydrogen bonds between adjacent amino acids and tRNA molecules detach and pick up another amino acid the ribosome moves along to the next codon on the mRNA molecule and a stop codon is reached a polypeptide is produced

Question 40

Give the two types of molecule from which a ribosome is made

Answer 40

One of rRNA and one of protein

Question 41

Describe the role of a ribosome in the production of a polypeptide do not include transcription in your answer

Answer 41

A ribosome attaches to the mRNA strand and moves along allowing tRNA anticodons to attach. two codons can fit at a time and ribosomes catalyses the formation of the peptide bond between amino acids .

Question 42

Explain why the percentages of bases from the middle part of the chromosome and the end part are different

Answer 42

They have different base, sequences and pre-mRNA transcribed from different DNA

Question 43

Different sequences of bases code for different proteins. Explain how

Answer 43

A protein is made of a chain of amino acids each amino acid has its own base

Question 44

How is DNA packed into a chromosome

Answer 44

-DNA molecule combines with histones
-DNA - histone complex is coiled
-coils fold to form loops
-loops coil and pack together to form the chromosome

Question 45

Suggest the role of the mRNA triplets stop codons

Answer 45

They stop translation and therefore resulting in ribosome detaching from mRNA chain

Question 46

describe how the production of mRNA in a eukaryotic cell is different from the production of mRNA in a prokaryotic cell

Answer 46

• mRNA in a eukaryotic cell contains introns whereas in a prokaryotic cell does not contain introns and pre - mRNA is produced