genetic information

Question 1

define gene

Answer 1

a sequence of DNA nucleotide bases that codes for a polypeptide or a functional RNA

Question 2

structure of DNA

Answer 2

double stranded molecule
each strand is a polynucleotide made up of individual nucleotides

Question 3

what is a DNA nucleotide composed of?

Answer 3

phosphate group
deoxyribose sugar
nitrogenous base

Question 4

describe the DNA in prokaryotes

Answer 4

circular DNA
some have smaller loops of plasmid
DNA is naked
not associated with histone proteins

Question 5

describe the DNA in eukaryotic chloroplasts and mitochondria

Answer 5

short circular molecule
not associated with histone proteins

Question 6

describe the DNA in the nuclei of eukaryotic cells

Answer 6

very long linear molecule
associated with histone proteins
DNA molecule and histone proteins forms a chromosome

Question 7

describe a homologous chromosome

Answer 7

-same genes of same loci
-centromeres at same place so same shape and size
-one maternal, one paternal

Question 8

how is a chromosome formed?

Answer 8

-DNA molecule is wrapped around histone proteins to fix in place
-DNA histone complex is coiled into solenoids

this means a very long molecule of DNA can be condensed into a single chromosome (a lot of info)

Question 9

what do humans have a diploid number of?

Answer 9

2n=46

Question 10

what do genes code for?

Answer 10

either:
-the amino acid sequence of a polypeptide
-a functional RNA (including rRNA and tRNA)

Question 11

where do genes occupy?

Answer 11

locus (fixed position)

Question 12

what is an exon?

Answer 12

parts of a gene which codes for amino acid sequences

Question 13

what are introns?

Answer 13

non-coding sequences

Question 14

define genome

Answer 14

complete set of all the genes in a cell

Question 15

define proteome

Answer 15

the full range of all the proteins that a cell is able to produce using its genome

Question 16

define allele

Answer 16

two or more versions of a genetic sequence coding for a different polypeptide

Question 17

define gene pool

Answer 17

all the different alleles of all the genes found within a population

Question 18

which amino acid does the start triplet always code for

Answer 18

methionine

Question 19

define triplet

Answer 19

every three bases in the sequence of a gene

Question 20

what does a triplet code for?

Answer 20

a specific amino acid

Question 21

how many different nucleotides are there in DNA?

Answer 21

4

Question 22

how many possible combinations of triplets are there to code for 20 amino acids?

Answer 22

4^3= 64

Question 23

define degenerate

Answer 23

in the genetic code, most amino acids are coded for by more than one triplet

Question 24

how many triplets dont code for amino acids in DNA?
what are they called?

Answer 24

3
stop triplets

Question 25

define universal

Answer 25

the same triplet always codes for the same amino acid

Question 26

define non-overlapping

Answer 26

each base is only read once, each base is part of only one triplet

Question 27

RNA structure

Answer 27

single stranded polynucleotide nucleotides composed of phosphate,ribose sugar and nitrogenous base (Uracil instead of Thymine)

Question 28

how long is messenger RNA?

Answer 28

few thousand nucleotides long

Question 29

what is every 3 bases called in mRNA?

Answer 29

codon

Question 30

what is the shape of mRNA?

Answer 30

linear molecule as bases don't bond to each other

Question 31

how long is transfer RNA?

Answer 31

about 75 nucleotides long

Question 32

describe the structure of tRNA

Answer 32

-strands fold back on themselves -hydrogen bonds form between complementary base pairs -shape is called clover leaf -one end is an amino acid binding site -3 of the bases are exposed called an anticodon

Question 33

how many different types of tRNA are there?

Answer 33

61

Question 34

why are there not 64 triplets?

Answer 34

because there are 3 stop codons which dont code for any specific amino acid

Question 35

how is a protein made in eukaryotes?

Answer 35

-specific gene is transcribed (introns and extrons) -this makes pre-mRNA -this is spliced to form mRNA -this is a copy of the exons of the gene only -mRNA is translated to make polypeptides

Question 36

describe transcription in the nucleus

Answer 36

-gene unwinds as hydrogen bonds between complementary bases broken by RNA polymerase -one strand acts as a template -complimentary free RNA nucleotides bind to exposed bases -in a condensation reaction, sugar phosphate backbone is joined using RNA polymerase -both inton and exon are transcribed to make pre-mRNA

Question 37

what disengages the RNA polymerase?

Answer 37

the stop triplet marking the end of a gene

Question 38

describe splicing in eukaryotic cells

Answer 38

pre-mRNA is spliced the non-coding sections (transcribed from the introns) are cut out and coding sections are edited together to produce mRNA

Question 39

what types of DNA dont need splicing? why?

Answer 39

prokaryotic DNA chloroplast and mitochondria DNA because they dont have introns

Question 40

where does translation happen? and what does it make?

Answer 40

cytoplasm makes polypeptides

Question 41

describe translation

Answer 41

-mRNA moves out of nucleus and attaches to ribosome. -tRNA carrying amino-acids bind by their anticodons to the mRNA - by complementary base pairing. -Another molecule of tRNA with another amino-acid attaches to the mRNA on the next codon along. - The two amino-acids on the tRNA form a peptide bond. -The first tRNA now moves away and a new tRNA attaches. - This process repeats, adding more amino-acids to the polypeptide-chain. -Process ends when a 'stop signal' is reached and completed polypeptide detaches.

Question 42

what does a gene mutation involve?

Answer 42

a change in the base sequence of a chromosome

Question 43

what are neutral mutations?

Answer 43

when the change in amino acid sequence does not affect the function of the protein

Question 44

why might some substitutions not result in any change?

Answer 44

genetic code is degenerate the new triplet may code for the same amino acid

Question 45

what are silent mutations?

Answer 45

in substitution mutation when the mutation causes no change

Question 46

what happens to the length of the polypeptide chain when the new triplet is a stop triplet?

Answer 46

shorter

Question 47

what does addition result in?

Answer 47

a frame shift

Question 48

what's the consequence of a frame shift?

Answer 48

new sequence of amino acids changes position of hydrogen and disulphide bonds

Question 49

what 2 mutations result in a frame shift?

Answer 49

addition deletion

Question 50

how can the rate of mutations be increase?

Answer 50

mutagenic agents

Question 51

x4 examples of mutagenic agents?

Answer 51

-high energy radiation -ionising radiation -chemicals eg tar in cigarette smoke -viruses

Question 52

what are carcinogens?

Answer 52

substances which cause mutations in oncogenes which cause the cell to become cancerous

Question 53

whats non-disjunction?

Answer 53

when homologous chromosomes do not separate in meiosis

Question 54

whats down syndrome caused from?

Answer 54

non-disjunction of chromosome 21