Topic 4: Genetics biodiversity and classification DNA

Question 1

Define Gene

Answer 1

A section of Dna that contains a code for making a polypeptide and funcitonal RNA. the code is a specific sequence of bases (amino acids).
polypeptides make proteins and so genes determine the proteins of an organism

Question 2

Define Allele

Answer 2

different versions of the sae gene found at the same locus on a chromosome

Question 3

Define Chromosome

Answer 3

in a eukaryotic cell nucleus dna is stored as chromosomes.
humans have 23 pairs or 46 in total
(one arm chromatid)
(centromere centre)
23rd pair x and y sex chromosomes (human karyotype)

Question 4

What is a locus

Answer 4

fixed position on a DNA molecule occupied by a gene

Question 5

what is a homologous pair

Answer 5

a hmoglous pair of chromosomes are exactly the same size, have the same genes but might have different alleles

Question 6

How is DNA stored in eukaryotes

Answer 6

DNA is stored as chromosomes inside of the nucleus
chromosomes are in linear shape/
to tightly coil the DNA to fit in the nucleus as chromosomes, the DNA is tightly wound around proteins called histones.
the complex on DNA wrapped around a hsitone is called a nucleusome

mitrochondria and chloroplasts contain prokaryotic-like DNA (because the are centre of reactions. DNA encodes for enzymes of reactions)

Question 7

How is DNA stored in a prokaryotic cell

Answer 7

prokaryotes also carry DNA in chromosomes, But the DNA molecules are short and circular the DNA is not wound around histones instead it supercoils to fit it

Question 8

Describe the prokaryotic like DNA in mitrochondria and chloroplast

Answer 8

similar to prokaryotic cells because its circular short and not histone bound.
mitrochondria and chloroplasts contain prokaryotic-like DNA (because the are centre of reactions. DNA encodes for enzymes of reactions)

Question 9

What are the three components of nucelotides

Answer 9

pentose sugar phosphate group and an organic base

Question 10

describe the structure of DNA

Answer 10

made up of deoxyribose sugar phosphate group on one of four rganic bases (A C G T) double stranded with hydrogen bonds between bases to form a helix shape

Question 11

What are the three features of the genetic code

Answer 11

1. degenerate- more than one triplet codes for the same amino acid (64 possible triplets for 20 amino acids)
   2.** universal-**same bases and sequences used by all species
2. non overlapping each triplet is only read once

Question 12

What is genetic code

Answer 12

The order of bases on DNA consits of codons (triplets of bases that code for a particualr amno acid)

Question 13

Describe the start and stop codon

Answer 13

At the start of every gene there is a ‘start codon’ TAC in DNA or AUG in mRNA it encodes for the amino acid methionine which is later removed from the protein if unecessary for the structure.

Stop codons- at the end of ever gene there are 3 bases that do not code for an amino acid these stop codons mark the end of a polypeptide chain ND CAUSE RIBOSOMES TO DETACH AND STOP TRANSLATION ATT ATC and ACT on DNA

Question 14

Describe how genetic code is degenerate

Answer 14

There are 20 amino acids that the genetic code has to be able to code for. there are four DNA bases (CGTA) and therefore three bases are needed to make enough comibinations to code for at least 20 amino acids.

The genetic code is degenerate because multiple codons (sequences of three bases) can code for the same amino acid.

4N 43=64codons→enough/more than.

this is an advantage as if a mutation occurs and codons will be different it may still code for the same amino acid and have no effect

Question 15

Describe how genetic code is universal

Answer 15

the same triplet of bases codes for the same amino acid in all organisms.

this is an advantage as it means genetic engineering is possible. e.g inserting the human gene for insulin into bacteria

Question 16

Describe how genetic coade is non overlapping

Answer 16

each base in a gene is only part of one triplet of baes that codes for one amino acid. therefore each codon or triplet bases is read as a discrete unit.

this is an advantage as if a point mutation occurs it will only affect one codon, and there fore one amino acid

Question 17

What are exons and introns

Answer 17

introns are sections of DNA that do not code for amino acids and thereofre polypeptide chains. they are found in eukayotic dna but not prokaryotic. these get removed, spliced out of Mrna molecules. foud between exons within genes

exons are sections that do encode for amino acids. separated by one or more introns. fo

Question 18

What is the genome and proteome

Answer 18

The genome is an organisms complete set of DNA in one cell. where as the proteome is the full range of proteins in one cell.

genome never changes and proteome constantly changes

Question 19

Descrive the function of RNA

Answer 19

the function of RNA is to copy and transfer the genetic code/info from DNA in the nucleus to the ribosomes. some RNA is also combined with proteins to create ribosomes for protein synthesis

Question 20

What is RNA structure

Answer 20

RNA is a polymer of a nucleotide formed of a ribose sugar , a nitrogenous base and a phosphate group. The bases are adenine guanine cytosine and urcail. relatively short polynucelotide chain and it is single stranded

Question 21

What are the three types of RNA

Answer 21

mRNA
tRNA
rRNA

Question 22

Describe the structure of mRNA

Answer 22

Messenger RNA is a copy of a gene from DNA
mRNA is created in the nucleur and leaves the nucleus to carry the copy of the genetic code of one gene to a ribosome in the cytoplasm

Question 23

Suggest advantages of using mRna rather than DNA for translation

Answer 23

shorter and contains uracil which breaks down quickly so no excess polypeptide forms.

short lived as it is only needed temporarily to help create a protein, by the time any enzymes could break it down it would have already carried out its function.

contains no introns

linear- ribosomes move along strand and tRNA bins to exposed bases

single stranded and every 3 bases in the sequenece codes for a specific amino acids

Question 24

Describe the structure of transfer RNA (tRNA)

Answer 24

a single strand of around 80 nucleotides that is folded over into a clover shape held in place by H bonds. one end is an anti codon on the opposite end is an amino acid binding site.

anti codons are complementary to codon on mRNA

Question 25

What is the function of tRNA

Answer 25

attatch to one of the 20 amino acids and transfer this amino acid to the ribosome to create a polypeptide chain. specific amino acids attacth to specific tRNA molecules and this is determined by 3 bases found on the tRNA which are complementary to the 3 on mRNA

Question 26

What is rRNA

Answer 26

Ribosmal RNA is the type of RNA that makes up the bulk of ribosomes

Question 27

Comapre DNA VS RNA

Answer 27

Differences between RNA and DNA monomers DNA contains the base thymine whereas RNA contains uracil instead. DNA contains the pentose sugar deoxyribose where as RNA contains the pentose sugar ribose. Differences between RNA and DNA polymers DNA is much larger and contains alot more genes. RNA is much shorter as it is only the length of one gene. DNA is doube stranded where as RNA is single stranded

Question 28

What are the two main stages of protein synthesis

Answer 28

production of protein froms from Dna. Transcription-where one gene on the DNA is copied into mRNA Translation- where mRNA joins with a ribosomes and the corresponding tRNA molecules brings the specific amino acid the codon codes for

Question 29

Outline the process of transcription

Answer 29

(takes place in nucleus) 1. DNA helix unwinds to expose the bases acting as a template 2. only one chain of DNA acts as template 3. Unwinding and unzipping is catalysed by DNA helicase 4. DNA helicase breaks the hydrogen bonds between bases 5. Free mRNA nucleotides in the nucleus align with opposite exposed complimentary dna bases 6. The enzyme RNA Polymerase bonds together the RNA nucleotides to create a new RNA polymer chain one entire gene is copied once copied the mRNA is modified and leaves the nucleurs through nucleur envelope

Question 30

How is pre-mRNA modified to become mRNA

Answer 30

Following transcription pre-mRNA has to be modified to become mRNA so that it is ready to leave the nucleaus and begin translation. The introns are spliced out by a protein called splicesome. leaving behind just the exons (the coding regions) then it moves out of the nucleurs and attatches to a ribosomes

Question 31

Outline the process of translation

Answer 31

(stage in which polypeptide chain is created using both mRNA sequence and tRNA takes places in cytoplasm on ribosomes) 1. Once mdoified mRNA has left nucleus and attatches to ribosome in the cytoplasm 2. The start codon (AUG) is recognised and ribosome attatches to it 3. a tRNA molecule with a complementary anti codon binds to the start codon (methionine) 4. The ribosome moves along the mRNA and a second tRNA with the next complemenrary anticodon binds to the next codon. this tRNA carries the next amino acid. 5. The ribosome joins the amino acids via peptide bond catalysed by an enzyme 6. the first tRNA is released (without amino acid) and the ribosome shifts to the next codon 7. this process repeats until the stop codon is reached at the end of mRNA and there is no tRNA with a complemnetary anticodon. instead a release factor binds and the polypeptide chain is released the polypeptide chain will enter golgi body for folding and modification

Question 32

What is meiosis

Answer 32

a form of cell division that produces four genetically different haploid cells (cells with half the number of chromosomes found in parent cell) known as gametes

Question 33

How is meiosis different from mitosis

Answer 33

meiosis: produces four genetically different cells with half number of chromosomes as the parent cells. two nucelur divisions. haploid cells (one set of chromosomes) introduces genetic variation mitosis: produces two genetically identical cells with the same number of chromosomes as parent cells one nucleur division. diploid cells (two sets of chromosomes)

Question 34

What happens during meiosis 1?

Answer 34

1. Homologous chromosomes pair up (forming bivalents). 2.Crossing over occurs between homologous chromosomes (at chiasmata), leading to genetic recombination. 3.Homologous chromosomes line up along the equator of the cell (metaphase I). 4.Independent assortment occurs — the orientation of each homologous pair is random and independent of the others. Homologous chromosomes are separated and pulled to opposite poles (anaphase I) by spindle fibres. Chromosomes are still in their duplicated form (each consists of two sister chromatids). Cell divides by cytokinesis to form two haploid cells, each with half the original number of chromosomes (but still as sister chromatids).